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Program for Array Seismic Studies 

of the Continental Lithosphere

Program for Array Seismic Studies 

of the Continental Lithosphere

Contents 

Introduction...................................................................................................................................................1 

Scientific Impact............................................................................................................................................2 

Exploring the Earth..................................................................................................................................................2 

Innovation in Data Acquisition and Analysis.......................................................................................................3 

Discovery...................................................................................................................................................................5 

High-Resolution Seismology................................................................................................................................11 

Earthquakes and Earthquake Hazards.................................................................................................................12 

Nuclear Explosions Seismology............................................................................................................................14 

Polar Efforts.............................................................................................................................................................14 

References................................................................................................................................................................17 

Program History.......................................................................................................................................19 

Timeline...................................................................................................................................................................20 

Instrumentation.........................................................................................................................................22 

Long-Term Passive Deployments.........................................................................................................................22 

Controlled-Source Instruments............................................................................................................................27 

RAMP: Rapid Array Mobilization Program.......................................................................................................28 

Support..................................................................................................................................................................29 

Equipment Support................................................................................................................................................30 

Shipping Support....................................................................................................................................................31 

User Training...........................................................................................................................................................31 

Experiment Support...............................................................................................................................................32 

Software Support.....................................................................................................................................................32 

Data Processing Support........................................................................................................................................33 

Interactions Between the IRIS Data Management System and PASSCAL Programs....................................34 

Cooperation with Other Facilities and Agencies..............................................38 

UNAVCO.................................................................................................................................................................38 

Network for Earthquake Engineering Simulation (NEES)...............................................................................38 

Ocean Bottom Seismograph Instrument Pool (OBSIP)....................................................................................39 

University-National Oceanographic Laboratory System (UNOLS)................................................................39 

US Geological Survey.............................................................................................................................................40 

Departments of Energy and Defense...................................................................................................................40 

Foreign Institutions and International Partnerships..........................................................................................40

Management and Oversight........................................................................................................42 

PIC Operations.......................................................................................................................................................44 

Trends and recent developments..........................................................................................46 

Usage Trends...........................................................................................................................................................46 

Personnel Trends....................................................................................................................................................50 

Broadband Sensors—Protecting Past Investments............................................................................................50 

Future Trends..........................................................................................................................................................51 

Budget....................................................................................................................................................................52 

Appendices 

A. PASSCAL Standing Committee and Past Chairs..........................................................................................53 

B. Policy for the Use of PASSCAL Instruments..................................................................................................54 

C. PASSCAL Data Delivery Policy.......................................................................................................................57 

D. PI Acknowledgement........................................................................................................................................59 

E. PASSCAL Instrument Use Agreement............................................................................................................60 

F. PASSCAL Field Staffing Policy..........................................................................................................................61 

G. Policy for an IRIS Rapid Array Mobilization Program (RAMP)................................................................62

Introduction 

When it was established in 1984, the Program 

for Array Seismic Studies of the Continental Lithosphere 

(PASSCAL) represented a fundamentally new direction 

for multi-user facilities in the earth sciences. At that time, 

the National Science Foundation (NSF) was encouraging 

exploration of new modes of collaboration in the development 

of community-based facilities to support fundamental 

research. The US seismology community organized a 

new consortium—the Incorporated Research Institutions 

for Seismology (IRIS)—to present to NSF a coordinated 

plan defining the instrumentation, data collection, and 

management structure to support a broad range of research 

activities in seismology. PASSCAL, along with the Global 

Seismographic Network (GSN) and Data Management 

System (DMS), were the initial core programs presented to 

NSF. In 1997, IRIS added an Education and Outreach (E&O) 

program, and in 2003, NSF expanded IRIS’s responsibilities 

to include the USArray component of EarthScope. 

PASSCAL provides and supports a range of portable seismographic 

instrumentation and expertise to diverse scientific 

and educational communities. Scientific data collected with 

PASSCAL instruments are required to be archived at the 

open-access IRIS Data Management Center (DMC). These 

two basic IRIS PASSCAL concepts—access to professionally 

supported, state-of-the art equipment and archived, standardized 

data—revolutionized the way in which seismological 

research that incorporates temporary instrumentation 

is practiced at US research institutions. By integrating planning, 

logistical, instrumentation, and engineering services, 

and supporting these efforts with full-time professional staff, 

PASSCAL has enabled the seismology community to mount 

hundreds of large-scale experiments throughout the United 

States and around the globe at scales far exceeding the capabilities 

of individual research groups. Individual scientists 

and project teams can now focus on optimizing science 

productivity, rather than supporting basic technology and 

engineering. Small departments and institutions can now 

compete with large ones on an equal footing in instrumentation 

capabilities. Scientists working outside of traditional 

seismological subfields now have the ability to undertake 

new and multidisciplinary investigations. Standardized 

equipment and data formats greatly advanced long-term 

data archiving and data re-use for novel purposes. 

PASSCAL has also influenced academic seismology in all 

parts of the world explored by US seismologists, and the 

program has on many occasions provided significant instrumentation 

to spur or augment international collaborations. 

Many of the standards and facilities pioneered by IRIS for 

instrumentation and data collection, archival, and open 

exchange have been adopted by other groups in the United 

States (such as permanent networks) and by seismological 

networks and organizations worldwide. This open-data culture 

has been embraced by other US data collection groups 

(seismological and nonseismological), and obligatory data 

archival requirements and standards have increasingly been 

stipulated by federal agencies. Internationally, similar portable 

seismograph facilities have patterned their operations on 

the PASSCAL model, although comprehensive international 

open data policies have not yet been universally adopted. 

This document summarizes the scientific research supported 

by the PASSCAL facility, reviews the history and 

management of the PASSCAL program, and describes the 

breadth of PASSCAL facilities and operations, focusing 

largely on the PASSCAL Instrument Center at New Mexico 

Tech in Socorro, New Mexico. PASSCAL and other IRIS 

core programs are funded by the NSF Earth Sciences 

Instrumentation and Facilities Program (David Lambert, 

Program Director). This report is part of a review of the IRIS 

PASSCAL facility required as part of the five-year (2006– 

2011) cooperative agreement (EAR-0552316) between NSF 

and the IRIS Consortium. The report reflects inputs from 

the PASSCAL Program Manager, Deputy Program Manager, 

Standing Committee Chair, PASSCAL Instrument Center PI, 

Director, and staff at New Mexico Tech, and IRIS community 

sources, including the PASSCAL Standing Committee, 

2005 PASSCAL strategic planning workshop participants, 

and 2007 Tucson PASSCAL Review Workshop participants.

Scientific Impact 

Exploring the Earth 

Since its inception, PASSCAL has provided instrumentation 

for field investigations in remote corners of the globe 

(Figure 1), with seismologists exploring Earth’s deep interior 

by mounting expeditions similar in spirit to the classic 

scientific expeditions of the eighteenth, nineteenth, and 

early twentieth centuries. Among the earliest PASSCAL 

controlled-source experiments were investigations in Iceland 

and Arctic Alaska. Subsequent controlled- and naturalsource 

investigations examined the evolution of Earth’s great 

orogenic plateaus and mountain systems: the Himalayan- 

Alpine chain, the Andes, and the North American cordillera 

and orogenic plateau. In Asia, PASSCAL investigators have 

conducted a series of large-scale seismic investigations 

throughout the Himalayas and across the Tibetan plateau, 

in the Tien Shan mountains, and other parts of the Alpine- 

Himalayan chain. In Latin America, investigations have 

extended from Tierra del Fuego through Chile, Argentina, 

and Boliva, to the Caribbean margin of Venezuela and on 

many Caribbean islands. In Central America, US seismologists 

have investigated the volcanoes and subduction zones 

of Costa Rica and Nicaragua. In North America, a large 

number of projects have been fielded from Mexico to the 

northern tip of Alaska, the Aleutian Islands, and the Bering 

and Chuckchi Seas. PASSCAL experiments have covered the 

great rift system of east Africa, from Tanzania to Ethiopia, 

and a number of the African cratonic provinces, notably 

the Kaapvaal. Elsewhere, US seismologists have deployed 

PASSCAL instruments from the Kola Peninsula in western 

Russia to the Kamchatka Peninsula in far eastern Siberia, 

and from Greenland to the South Shetland Islands. This 

tradition continues today with large projects on every continent 

and novel investigations in Antarctica utilizing recently 

developed special polar equipment. 

Unlike the typical laboratory investigations of many sciences, 

the seismologist’s laboratory is the Earth, which makes seismic 

fieldwork both exciting, and also logistically and physically 

challenging (and sometimes dangerous). PASSCAL 

instruments have been deployed from almost every means 

of conveyance available, from ships, light aircraft, and helicopters; 

to light water craft and four-wheel-drive vehicles; 

to horses, donkeys, and backpacks. Instruments have been 

deployed in locations ranging from mountaintops to fjords, 

from the slopes of volcanoes to ice sheets and glaciers, and 

in tropical rain forests and deserts, and on desert islands. 

PASSCAL instruments have been damaged from excessive 

heat and cold, flooding, vehicle wrecks, landslides, 

mudslides, volcanic ejecta, and local wildlife (notably bears). 

Instruments have been stolen, deliberately shot, investigated 

by the local law enforcement agencies of several countries, 

paved over by road construction crews, and in one instance, 

destroyed by a native spear. 

The experiment-planning stage for instrument deployments 

everywhere in the world is becoming increasingly difficult 

and lengthy in nearly all environments, as seismologists 

and support staff are faced with ever-increasing numbers 

of permits to obtain, often from a variety of different 

agencies, and as experiments continue to grow in numbers 

of instruments. Global urbanization is posing new and 

challenging problems; cities are high-seismic-noise, densely 

packed, theft-prone environments. An example of careful 

planning in the urban environment is the successful series 

of controlled-source experiments conducted in the Los 

Angeles basin by the US Geological Survey and a team of 

university collaborators. Fielding over 1000 seismographs, 

these experiments deployed instruments in the backyards 

of residents throughout the greater metropolitan area, 

and detonated explosives in drillholes on public lands that 

included national forests, military facilities, watershed and 

flood-control lands, and even on school grounds.

La RISTRA, New Mexico. 

Tibet. Locals help with installation 

of a station. 

Alaska. STEEP experiment. 

Venezuela. Transporting gear 

the old fashioned way. 

PASSCAL Stations 

60 

0 

Figure 1: Global 

extent of station 

coverage for the history 

of the PASSCAL 

program, now totaling 

more than 

3800 stations. 

-60 

180 -120 -60 0 60 120 180 

Tiwi. Specialized enclosure 

for a rainy environment. 

Chile. Installing an intermediate 

period sensor. 

Kenya. A short period station 

being serviced while local 

Masai look on. 

Mt. Erebus. An intermediate 

period sensor is installed 

directly onto the bedrock 

flanking the volcano. 

Innovation in Data Acquisition and Analysis 

The initial desire for a single multi-use PASSCAL instrument 

proved to be excessively restrictive for community needs, 

and the instrument pool has evolved today into a small suite 

of specialized equipment packages, with many investigations 

making use of multiple instrumentation types and associated 

methodologies during a single project. For most earthquakerecording 

applications, PASSCAL stations are self-contained. 

Installations include solar and battery power, independent 

GPS clocks, large data-storage capabilities, usually broadband 

(120 s) or intermediate (30 s) period instruments and, 

if available, communication links facilitated by satellite, lineof-sight 

radio, and Internet or telephone networks. In contrast, 

crustal-scale, controlled-source experiments require 

rapid deployment and recovery of large numbers of instruments 

that have lower storage capacities and power requirements. 

These community needs led to the development

permit advanced wavefield imaging using P-to-S and S-to-P 

scattered waves from teleseismic sources, and multiply 

reflected P-wave signals, and provide structural velocity 

and impedance images with roughly an order of magnitude 

greater resolution than comparable transmission tomography 

(e.g., Bostock et al., 2001, Rondenay et al., 2001). These 

methods provide, for the first time, images of the upper 

mantle with resolution comparable to crustal images using 

controlled-source methods. Even common conversion point 

stacking (Dueker and Sheehan, 1997), which is less sensitive 

to spatial aliasing, can provide remarkably detailed images of 

crustal structure from teleseismic signals (Figure 2), although 

increasingly, single or multimode migration methods and/or 

scattering inversions are being pursued (e.g., Bostock et al., 

2002; Wilson and Aster, 2005) (Figure 3). 

In controlled-source seismology, PASSCAL instruments 

have long been used for traditional two-dimensional 

refraction and reflection profiles, but the growing number 

of University of Texas, El Paso (UTEP), PASSCAL, and 

EarthScope TEXAN instruments now permits threedimensional 

surveys across relatively large areas. The crustal 

tomography community has been developing three-dimenof 

the RT125 (“TEXAN”) instrument. Many tens of these 

instruments can be deployed or recovered by a single team 

in a day. Demand for high-resolution reflection imaging of 

the shallow (< 1 km) subsurface required purchase and support 

of commercially available cable reflection systems. 

The availability of large numbers of each instrument type 

has followed or encouraged development of new analysis 

techniques that are either theoretically impossible or practically 

inconceivable for small numbers of instruments and 

low data volumes. For example, large aperture, increasingly 

dense, and increasingly two-dimensional arrays of broadband 

seismographs allow the identification and removal 

of multipath interference in surface wave measurements 

(Forsyth and Li, 2005), a longstanding problem in surface 

wave analysis. Cross correlation of the microseism noise 

field to estimate surface wave Green’s functions between 

stations in large, dense arrays has opened a whole new field 

of investigation of the crust and upper mantle with surface 

waves in the 5–40 s band (Shapiro et al., 2005). Similarly, 

large-aperture, dense arrays make correcting for Fresnel 

zone phenomena in body wave tomography possible, 

removing the ray-theoretical assumptions inherent in travel 

time methods, and providing improved 

images of the subsurface (Dahlen et al., 

2000; Dahlen and Baig, 2002; Nolet et 

al., 2005). Anisotropy measurements 

made from shear-wave splitting across 

large dense arrays can reveal systematic 

variations in orientation that can be 

related to asthenospheric flow directions, 

often associated with plate edges, 

subduction zones, and mantle upwellings 

(e.g., Savage and Sheehan, 2000; Fischer 

et al., 2005; Walker et al., 2005; Zandt 

and Humphreys, in press). The seeming 

chaos of splitting directions observed 

across a coarse array can be geodynamically 

meaningful when viewed across 

a dense array. 

The densest broadband arrays now 

provide spatially unaliased recordings 

of teleseismic signals to relatively high 

frequencies (0.5–1 Hz). Such data sets 

Figure 2 Common conversion point (CCP) stacked receiver function image from an aereal 

array of broadband seismographs in Montana showing details of crustal structure. The thick 

lower crustal layer was first identified in a complementary PASSCAL controlled-source 

experiment deployed in the same region. (From Yuan et al., 2006)

very forearcs lowincluding surface heat Cascadia flow 10,11 (30–40 . In mWm Fig. 2b 22 ) we observed plot a in thermal 

most 

from distance ,40 of to ,50–100 .80 mWm km. 22 However, over ,20 a landward km signals increase an abrupt in heat increase 

flow 

model forearcs for including central Oregon Cascadia 12 corresponding 10,11 . In Fig. to 2bthe we teleseismic plot a thermal profile, 

from in deep ,40 temperatures. to .80 mWm In particular, 22 over ,20 Moho km signals temperatures an abrupt beneath increase the 

model for central Oregon 12 corresponding to the teleseismic profile, 

arc in deep and temperatures. backarc are significantly In particular, higher, Moho temperatures above 800 8C. beneath Thus ser- 

the 

pentine arc and should backarcexist arein significantly that portion higher, of the mantle above 800 forearc 8C. contained 

Thus ser- 

within pentinethe should dashed exist square in that in portion Fig. 2b, of but the it will mantle not forearc be stable contained beneath 

the within arc the and dashed backarc. square The in degree Fig. 2b, of but serpentinization it will not be stable in the beneath forearc 

will the sional arc depend and travel upon backarc. time thetomography The amount degree of H of methods for about the last 

2 O serpentinization that chemically interacts the forearc with 

will forearc 10 years depend mantle, and upon can which, the easily amount inexploit turn, of Hdepends the 2 O that expanded chemically on H 2 instrument O flux interacts frombase 

with the 

forearc subducting mantle, slab which, and the inpermeability turn, depends structure on H 

(e.g., Hole, 1992; Zelt and Barton, 1998). 

2 of O the fluxslab, fromplate 

the 

interface subducting and slab mantle. 

and the permeability structure of the slab, plate 

interface Serpentinite and mantle. exhibits elastic properties that are unique among 

commonly 

Theoretical Serpentinite occurring 

developments exhibits rock elastic types, 

and properties notably 

advances 

low that 

in 

elastic 

computational 

are unique wave velocities 

among 

and commonly high Poisson’s occurring ratio. rockThe types, very notably low S-velocity low elastic of wave serpentinite velocities is 

central and capabilities, highto Poisson’s thecoupled interpretation ratio. with Theseveral very of our low community results. S-velocity In particular, of efforts serpentinite its S- 

is 

velocity central 

methodological to(v the S ) is interpretation significantly exploration, of lower and our 

in than results. 

software that In of standardiza- 

particular, its peridotitic 

its S- 

protolith velocity (v(dv S < 2 2 km s 21 S ) is significantly) lower and commonly than that of occurring its peridotitic lower- 

protolith crustal tion and lithologies (dv dissemination (dv (e.g., S < 1 km s Computational 21 S < 2 2 km s 21 ) and) 13 commonly . Figure 3 shows Infrastructure 

occurring the S-wave 

lowercrustal 

velocity for Geophysics lithologies of mantle [CIG] (dv peridotite and Seismic S < 1 kmsamples s 21 ) 13 . wave Figure as a Propagation function 3 showsof the degree and 

S-wave of 

serpentinization velocity of mantle at a peridotite pressure of samples 1 GPa, which as a function is appropriate of degree for the 

of 

base serpentinization Imaging 

of a ,35-km-thick Complex at a pressure media 

continental of[SPICE]) 1 GPa, crust which are 

as 

facilitating is presented appropriate in 

the 

ref. for the 14. 

Correction base increased of a ,35-km-thick application from room of temperature continental waveform crust tomography 400–500 as presented 8C(i.e., will infull 

shift ref. this 

14. 

curve Correction downward from room to velocities temperature 0.1–0.2 tokm 400–500 s wavefield inversion) to two-dimensional, 21 lower. 8C will This shift information 

downward allows us to interpret velocitiesthe 0.1–0.2 image kmin s 21 Fig. lower. 2a quantitatively 

This infor- 

in mation land, terms marine, allows of degree us and to ofonshore-offshore serpentinization interpret the image ininvestigations the forearc Fig. 2amantle. quantitatively to provide As in a 

previous in 

this 

controlled-source 

curve 

extremely terms of study degree 

high-resolution 3 , we ofinterpret serpentinization 

images the change of in 

velocity the in forearc dip of and the mantle. 

density subducting 

As a 

plate previous by 45 study km 3 depth , we interpret to indicate the the change onset inof dip eclogitization of the subducting of the 

oceanic plate variations bycrust, 45 km in leading, crust. depthAlthough to eventually, indicatestill to thea a onset 15% computational increase of eclogitization in density challenge, 

of and the a 

pronounced oceanic 

three-dimensional crust, reduction leading, 

waveform eventually, in the seismic inversion to a 15% contrast increase 

of large with in 

data density underlying sets and 

for 

a 

oceanic pronounced mantle reduction 15 . 

in the seismic contrast with underlying 

oceanic controlled Although mantle and a continuous 15 . natural sources dehydration is within of downgoing sight. oceanic crust 

and Although entrained a continuous sediments is dehydration expected, the of downgoing water released oceanic by eclogi- 

crust 

tization and entrained (between sediments 1.2 and is3.3 expected, wt%; ref. the 16) water is especially released important 

by eclogitization 

expulsion (between into 1.2the and overlying 3.3 wt%; mantle ref. 16) wedge, is especially where important it causes 

hydration for teleseismic expulsion andwavefields, into serpentinization, the overlying and three-dimensional and mantle significantly wedge, active-source 

where diminished it causes velocities. 

hydration The 

Enhanced experimental developments, well-sampled 

for 

arrays, coupled and horizontal serpentinization, boundary 

with theoretical and near 

and significantly 32 km depth 

data processing 

diminished and between 

vel- 

2122.6 ocities. The and 2123.38 horizontal longitude boundary that near juxtaposes 32 km depth high- and (or neutral-) 

between 

velocity 2122.6 advances, and material are 2123.38 significantly above longitude withadvancing low-velocity that juxtaposes geological material high- and below (orgeody- 

neutral-) is thus 

inferred velocity 

namic insight to material manifest into above the Earth highly with 

history low-velocity unusual and occurrence processes. materialof Increasingly 

below an ‘inverted’ 

is thus 

continental inferred to manifest Moho separating the highlylower-crustal unusual occurrence rocks from of an underlying, 

‘inverted’ 

continental detailed seismic Moho structural separating imaging lower-crustal now rocks permits frominterpreta- 

underlying, 

tion of chemical- and phase-change boundaries, and more 

useful inferences on the presence or absence of free fluids 

or hydrated materials. This advance, in turn, allows the 

seismological community and an increasing diversity of 

collaborators in geology, geodynamics, and geochemistry to 

Figure 23. Comparison Scattered of wave scattered image wave made inversion using results a generalized with thermal Radon model. a, S- 

advance understanding of fundamental Earth processes. 

velocity Figure Transform 2perturbations Comparison inversion below of of scattered the P-to-S array, wave converted recovered inversion from waves results the from inversion with thermal a dense of scattered model. a, waves S- in 

the velocity broadband P-wave perturbations coda array of 31 across below earthquakes the the array, Oregon recorded recovered Cascadia at from teleseismic thesubduction inversion distances. of scattered zone, The image 

waves in 

represents the superimposed P-wavea coda bandpass-filtered of on 31a earthquakes thermal version model recorded of of true the at teleseismic perturbations subduction distances. to zone, a one-dimensional, 

The and image an 

smoothly represents interpretation varying a bandpass-filtered of reference the image. model. version The Discontinuities loss of theof true signal perturbations present from the where to continental 

a one-dimensional, 

steep changes in 

perturbation smoothly Moho in varying the polarity mantle reference occur. forearc b, model. Thermal is Discontinuities attributed model of Cascadia to aremantle present subduction serpentinization wherezone steep corresponding 

changes by 

approximately perturbation fluids released polarity to the 

from occur. profile 

the b, in 

subducting Thermal a. cool model subducting 

plate. of Cascadia (From 

plate subduction Bostock 

depresses zone et 

isotherms 

al., corresponding 2002. 

the 

forearc, approximately Field experiment 

rendering to the serpentine profile described instable a. The in 

within 

Nabelek coolthat subducting portion 

et al., 

of plate 1993.) 

the mantle depresses encompassed isotherms in by the 

dashed forearc, rectangle; rendering serpentine solid lines stable indicate within locations that portion of subducting of the mantle oceanic encompassed crust and 

by the 

continental dashed rectangle; Moho. solid Note lines temperature indicatecontour locations interval of subducting is 200 8C. oceanic c, Interpretation crust and of 

structure continental in Moho. a. High Note degrees temperature of mantle contour serpentinization interval is where 200 8C. the c, subducting Interpretation oceanic 

of 

crust structure enters in the a. High forearc degrees mantle ofresults mantlein serpentinization an inverted continental where the Moho subducting (high-velocity oceanic crust 

on crust Discovery 

low-velocity enters themantle), forearc mantle which results gradually in an reverts inverted eastward continental to normal Moho polarity (high-velocity by 2122.38 

crust Figure 3 S-velocity of altered peridotite as a function of degree of serpentinization. Data 

longitude. low-velocity The signature mantle), which of the gradually subducting reverts oceanic eastward Moho to diminishes normal polarity with depth by 2122.38 as a 

from Figure ref. 3 14. S-velocity Bold line of altered shows peridotite best-fit linear as aregression function ofwith degree ^1j of error serpentinization. bounds. The 

Data 

result longitude. progressive The signature eclogitization of the subducting below 45 oceanic km. Inverted Moho triangles diminishes in with a and depth c show 

as a 

from predicted ref. 14. velocity Boldcontrast line shows at the best-fit wedge linear corner regression suggests with degrees ^1j error of serpentinization bounds. The as 

instrument result Over of85 progressive locations. institutions eclogitization contributed below 45 km. “one-pager” Inverted triangles research in a and csum- 

show 

high predicted shaping as 50–60%. velocity current contrast v S , S-wave scientific at the velocity. 

wedge discussions corner suggests about degrees Earth of serpentinization processes. 

as 

instrument 

maries, attributed locations. 

to PASSCAL instrumentation, to the 2005 

high 

Because as 50–60%. 

seismic v S , S-wave 

exploration velocity. 

of the Earth has never before 

NATURE | VOL 417 | 30 MAY 2002 | www.nature.com © 2002 Nature Publishing Group 

537 

NATURE IRIS proposal. | VOL 417 | 30These MAY 2002 summaries | www.nature.com provide a representative 

© 2002 Nature Publishing been Group undertaken at the spatial and temporal scales of the 

537 

overview of the variety of seismic experiments currently GSN and the aggregate of PASSCAL experiments, serendipitous 

discoveries are quite common. 

being fielded that is more comprehensive than space allows 

in this review. Here, we note a few key themes that are

Subduction and Whole-Mantle Convection 

The cover graphic on the April 1997 issue of GSA Today, 

showing the subducted Farallon plate beneath North 

America in P and S wave global tomograms (Grand et al., 

1997), helped to forever change the debate in the earth 

science community about whole mantle versus layered 

mantle convection (Figure 4). Although primarily a result of 

measurements made on observatory seismographs, global 

tomographers are increasingly including data from the great 

number of PASSCAL broadband deployments around the 

globe to enhance resolution in their studies. This data use 

has driven a new policy that every PASSCAL broadband 

experiment is now required to declare one station open to 

the larger community as soon as it is installed. Note that all 

data become available after a maximum two-year period. 

Tomographers are providing ever more accurate images of 

the global plate circulation system at depth throughout the 

world. Dozens of PASSCAL experiments have been fielded 

with the goal of examining the primary convection system, 

(A) 

2770 km 

depth 

and an increasing number are being undertaken to investigate 

the secondary convective processes that modulate the 

whole mantle system and that often drive regional tectonics. 

PASSCAL experiments have been designed to provide structural 

images and infer processes in a wide range of subduction 

zones, the most obvious manifestation of the primary 

convection system. In northern China, a PASSCAL experiment 

will measure the spatial extent, and therefore length of 

time, the subducted Pacific slab rests on the 660-km phase 

transition beneath northern China before descending into 

the deeper mantle as the Japan trenches roll back. A series 

of passive- and controlled-source seismic experiments 

are examining the complex arc-continent collision of the 

Eurasian and Philippine plates that formed Taiwan, and the 

accretion of Taiwan to the Asian mainland. The controlledsource 

experiment is designed to relate surface structures in 

the Taiwan crust to the mantle deformation field. Combined 

land and marine experiments have investigated the structure 

of the backarc and slab of the Tonga-Fiji and Marianas 

trench systems, with complementary controlled-source 

experiment to examine evolution of oceanic island arc crust 

and back arc crust. Combined land-marine passive- and 

controlled-source experiments are examining the complex 

southeastern Caribbean plate boundary where the Atlantic- 

South America plate forms a slab tear edge propagator 

fault (STEP fault; Govers and Wortel, 2004) as the Atlantic 

subducts beneath the Caribbean plate. Simultaneous tearing 

and deformation of the South American lithosphere 

control mountain building and basin development along the 

northern South American margin. The causes and tectonic 

consequences of trench rollback in the Adriatic and Hellenic 

arcs are being determined by projects in the central and 

eastern Mediterranean. Other subduction zone experiments 

have examined the consequences of tears in or terminations 

of subducting plates in Mexico and the northwest Pacific, 

and the hydration state of slabs in Central America. 

(B) 

FARALLON SLAB 

2770 km 

depth 

Figure 4. Cover graphic from GSA Today showing the subducted 

Farallon plate beneath North America. (From Grand et al., 1997) 

The Andes mountains and Altiplano-Puna plateaus are 

being investigated because they form one of Earth’s great 

mountain chains and orogenic plateaus, and also because 

they are viewed by many as an analog to the western United 

States ~ 40–50 million years earlier in its history. These 

regions thus shed light on the complex Cenozoic history 

of western North America. For example, basement rooted,

Laramide-style uplifts occurring in South America are 

similar to those found in the Southern Rockies that formed 

~ 55 Ma. Andean studies provide a natural laboratory for 

contrasting lithospheric deformation and volcanic patterns. 

These patterns range between flat-slab subduction near 30°S, 

which is producing a volcanic gap with characteristic basement-rooted, 

Laramide-style uplifts, to steep slab subduction 

at 36°S, where a normal volcanic arc exists. 

depth (km) 

0 

100 

200 

300 

400 

500 

600 

Fiji LR CLSC VF 

dVp km/s 

200 400 600 800 1000 1200 1400 

Active and passive seismic experiments employing land and 

ocean bottom seismographs have probed subduction-related 

processes in the accretionary wedge, the seismogenic zone, 

the oceanic crust, and mantle wedge in a variety of trenches, 

including those in Central American, Cascadia, Alaska, 

and the western Pacific (Figure 5). In Cascadia and Alaska, 

high-resolution scattered wave and tomographic images of 

the descending plate and the mantle wedge have been used 

to identify zones of hydration and serpentinization in the 

mantle wedge, and track dehydration and eclogization of 

subducting oceanic crust. 

The Indian-Asian plate collision zone has produced Earth’s 

most extreme topography as ocean-continent subduction 

evolved into continent-continent collision. A large 

number of recent PASSCAL-supported controlled- and 

natural-source experiments have produced a much greater 

understanding of large-scale orogenesis and its structural 

underpinnings. In the early investigations in Tibet, for 

example, combined controlled- and passive-source investigations 

identified a wide-spread midcrustal low-velocity zone 

beneath the Tibetan plateau that is topped by seismic bright 

spots. These observations have been interpreted as a plateauwide 

partial melt zone, capped by either lenses of melt and/ 

or melt-derived fluids. A similar widespread zone of partial 

melt was subsequently identified under the Altiplano of the 

Andes. More recent experiments have examined mantle 

flow fields created adjacent to the edges of collision zone, as 

Eurasia deforms in response to the collision. The seismologic 

database in Tibet and the Himalayas have led to several 

models of lithospheric descent under the Tibetan plateau; 

debate still exists as to whether the lithosphere consumption 

is one-sided or two-sided (i.e, whether the Indian mantle 

lithosphere is subducting alone, or both Indian and the 

Eurasian mantle lithosphere are descending into the mantle). 

depth (km) 

depth (km) 

dVp km/s 

0 

100 

200 

300 

400 

500 

600 

Fiji 

dVs km/s 

0 

100 

200 

300 

400 

500 

600 

dVp/Vs 

0.6 0.4 0.2 0 0.2 0.4 0.6 

LR 

CLSC 

dVs km/s 

Figure 5. Mantle seismic velocity structure of the Tonga subduction 

zone and Lau back arc basin as determined by broadband ocean 

bottom seismometers and PASSCAL instruments. Crustal structure is 

constrained by seismic refraction results. The figure shows (a) dVp, (b) 

dVs, and (c) d(Vp/Vs) anomalies relative to the IASP91 velocity model, 

contoured at 0.08 km/s for Vp, 0.06 km/s for Vs, and 0.012 units for 

Vp/Vs. Earthquake hypocenters are shown as black circles. The central 

Lau spreading center (CLSC) shows a large dVp/Vs anomaly in the 

uppermost mantle extending to ~100 km depth, with an anomaly 

amplitude larger than expected from thermal effects alone, suggesting 

a wide zone of melt production. (From Condor and Wiens, 2006) 

VF 

200 400 600 800 1000 1200 1400 

Fiji 

0.5 0 0.5 

LR 

CLSC 

VF 

dVp/Vs 

200 400 600 800 1000 1200 1400 

distance (km) 

0.1 0.05 0 0.05

Hotspots and Plumes 

Source-region depths for Earth’s hotspots, which have topographic, 

geothermal, and magmatically distinct signatures 

at Earth’s surface, have been seriously debated since before 

the theory of plate tectonics was proposed. Most recent 

discussion has focused upon whether they originate near the 

core-mantle boundary or in the upper mantle (or perhaps 

both). Global tomography with improved imaging capabilities, 

in some cases augmented with archived PASSCAL data 

is gradually determining that some source zones may indeed 

be at the core-mantle boundary, whereas others arise at shallower 

levels. A number of PASSCAL experiments have been 

carried out in recent years explicitly to address this debate. 

The Yellowstone caldera and hotspot have been the target of 

multiple PASSCAL experiments that identified low crustal 

velocities associated with surface thermal anomalies. Deeper 

imaging revealed a low-velocity pipe to the north-northwest 

of Yellowstone that is associated with a downward-deflecting 

410-km discontinuity and extends at least as deep as the 

660-km discontinuity, although it does not appear to penetrate 

the bottom of the transition zone. A related PASSCAL 

experiment across the Snake River plain to the southwest 

identified a high-velocity lower crust, interpreted as a frozen, 

plume-derived basalt intrusion 

atop a low-velocity upper mantle. 

(a) 

Seismic velocity and anisotropy 

interpretations ascribe the upper 

mantle anomaly to the flow of 

-200 

0 

a plume head, flattened and 

stretched by the overriding North 

-400 

American plate. 

Iceland has also been the site of 

several recent PASSCAL experiments 

(e.g., Figure 6). Integrated 

tomography and receiver-function 

imaging suggest that the 

plume extends at least to the 

top of the transition zone at the 

410-discontinuity. Receiver func- 

0 

-200 

-400 

tions suggest it may extend to its base, but the most recent 

global tomography suggests it is an upper mantle feature. 

This is still a very controversial topic. 

Global tomography data sets have been complemented by 

data from a number of PASSCAL experiments in the quest 

for plume sources. For example, data from the Kaapvaal 

PASSCAL seismic array has helped quantify the large-scale 

low-velocity zone at the core-mantle boundary under the 

southern Atlantic that extends under East Africa, the site of 

a developing continental rift system. A variety of PASSCAL 

active- and passive-source seismic experiments examined 

the details of the East African rift system from Tanzania 

through Ethiopia, finding large volumes of basaltic additions 

to the crust, and relatively narrow low-velocity zones 

in the mantle through upper mantle depths. Processes 

in the uppermost mantle directly beneath the crust are 

still poorly understood. 

Relatively thin crust and low upper mantle velocities in 

the Basin and Range province have been identified by a 

COCORP survey at 40°N and a number of controlled-source 

and broadband PASSCAL experiments. Until recently, 

tomographic images of the Basin and Range mantle relied 

largely on the existing earthquake monitoring seismograph 

0 200 400 600 

0 

0 200 400 600 

0 

(b) 

-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 

percent velocity anomaly 

Figure 6. Tomographic images of Vs perturbation along two cross sections through Iceland showing the 

vertical plume conduit resolved to 200–400-km depth, and the plume head above 200 km. Anomalies 

are absolute velocity variations across (a) and parallel (b) to the rift zone as a percentage deviation 

from 4.5 km/s in the upper 210 km. Below 210 km, the percentages are relative to layer averages. 

Relative velocity anomalies (c and d) show velocity variations within the plume head including high 

velocities in the uppermost mantle above the plume core. (From Allen et al., 2002) 

-200 

-400 

-200 

-400 

0 200 400 600 

0 

(c) 

0 200 400 600 

0 

(d) 

-2 -1 0 1 2 

percent velocity anomaly

network, but are now being rapidly refined using data 

from the first USArray Transportable Array footprint. 

Explanations for the positive buoyancy required by the 

excess elevation and thin crust include “simple” orogenic 

collapse over an already perturbed mantle wedge following 

the Sevier and Laramide orogenies, a mantle plume impacting 

the entire region, and asthenospheric upwelling induced 

by Farallon plate removal. Each of these scenarios has 

different consequences for support of the Basin and Range 

lithosphere, ranging from an almost entirely thermal origin, 

to a mixed mode of thermal and chemical buoyancy, likely 

modulated by water added to the upper mantle over time by 

the Farallon plate. A remarkable circular anisotropy pattern 

in the central/northern Basin and Range has been attributed 

to the plume impact, or to toroidal asthenospheric flow arising 

beneath the edge of the descending Gorda/Juan de Fuca 

plate. A PASSCAL-facilitated study of the Rio Grande rift, 

marking the extreme eastern extent of Basin and Range-type 

extension, showed that it has an entirely uppermost mantle 

expression confined well above the 410-km discontinuity. 

The Upper Mantle and Secondary 

Convection Phenomena 

Several secondary convection mechanisms that are key to 

the history of Earth’s continental crust have been suggested, 

notably Rayleigh-Taylor instabilities and delamination 

processes, in which negatively buoyant mantle lithosphere 

and sometimes mafic lower crust are recycled into the 

deeper mantle without being part of a larger subducting 

plate system. A number of these have been subsequently 

identified by PASSCAL-supported projects. Rayleigh-Taylor 

instabilities were first predicted theoretically (Houseman et 

al., 1981), and somewhat later delamination processes were 

inferred from geochemical data in the Andes (e.g., Kay and 

Kay, 1990, 1993). These processes heavily modulate regional 

tectonics and magmatism, yet the triggers of the instabilities 

are not observable at the surface. Their a posteriori surface 

signatures are identifiable in local or regional thermal perturbations, 

in the magmatic record, and in abrupt changes in 

elevation. Various types of seismic investigations can identify 

descending lithospheric drips and the unusual crustal 

structures that ephemerally persist following delamination. 

Active- and passive-source PASSCAL experiments have 

examined probable mantle drips (1) in the Sierra Nevada, 

where a lithospheric keel is thought to have foundered from 

the batholith base, producing a characteristic suite of surface 

volcanics, (2) in the Wallowa Mountains, where a bull’s-eye 

uplift of a granitic pluton is associated temporally and 

spatially with the Columbia River flood basalts, (3) across 

the Rio Grande Rift and Colorado Plateau, and (4) in the 

Vrancea zone, Romania, where intermediate-depth seismicity 

and a mantle slab have been identified far from a typical 

subduction zone. 

Ancient Boundaries and Modern Processes 

Southwestern North America was assembled in Paleo-proterozoic 

times by successive accretion of island arcs to the 

Archean Wyoming protocontinent over some 600 million 

years. A suite of active and passive seismic experiments 

across the terrane boundaries separating these ancient island 

arcs in the southern Rocky Mountains show that the modern 

upper mantle has a fabric parallel to the northeastern trend 

of the Precambrian fabric, rather than the more north-south 

trend of the modern plate boundaries. These seismic data 

led to the insight that ancient lithosphere-scale mantle 

structure persists and controls much of modern tectonics in 

the western United States not directly affected by Farallon 

subduction. Upper mantle seismic velocities are low along 

northeasterly trends beneath a number of the terrane 

boundaries. One such feature is along the Jemez lineament, 

a trend of Cenozoic volcanics following the southeastern 

flank of the Colorado Plateau into the Great Plains, and 

crossing the east-west rifting of the Rio Grande. Combined 

controlled- and passive-source PASSCAL experiments such 

as CD-ROM and RISTRA identified a thinned crust and a 

mantle source for recently erupted basalts in northern New 

Mexico and showed dramatic and largely unanticipated 

uppermost mantle velocity contrasts associated with ongoing 

interactions between the Proterozoic boundaries, Laramide 

compressional, and Cenozoic extensional structures. A 

prominent and presently enigmatic mantle feature, which 

probably has a similar mixed provenance related to the interactions 

of ancient structures and recent tectonics, is in the 

Aspen Anomaly region of central Colorado. This structure 

underlies the highest topography of the present-day Rocky 

Mountains, and is now being investigated in a continental 

dynamics experiment embedded within the EarthScope 

USArray Transportable Array.

The Cratons 

The Archean cratons of Africa and North America have been 

extensively studied in PASSCAL-supported experiments. 

Four notable experiments are the Trans-Hudson, MOMA, 

Abitibi experiments in North America, and the Kaapvaal 

experiment in South Africa. The TransHudson experiment 

provided the first data to suggest that the anisotropy field 

beneath the cratons was related to absolute plate motions 

and resultant mantle shear strain, which was subsequently 

supported by observations in many other locations. The 

MOMA experiment identified the southern edge of the 

Canadian shield, showing distinct structures north and 

south of the array. The Kaapvaal experiment identified small 

positive velocity anomalies that have been interpreted as a 

tectonospheric root extending up to ~ 300 km (Figure 7). 

The Abitibi experiment data were used to make scattered 

wave images of apparent Grenville age subduction structures 

along the southeastern flank of the Superior province, 

contributing to our understanding of cratonic evolution and 

deformation (Figure 8). 

The Continental Crust 

The processes by which continental crust and underlying 

lithosphere forms and persists for up to gigayears has 

been a longstanding geological problem with fundamental 

implications for continental evolution and the history of plate 

tectonics. There appears to be no direct differentiation path 

from fertile mantle to bulk continental crust. Some intermediate 

differentiation processes must occur to produce a crust 

with the chemical properties recorded in sediments and also 

inferred from seismic data (~ 62% Si0 2 

). Field evidence suggests 

cratonic crust is an aggregation of island arcs; however, 

seismic evidence suggests that modern island arcs are too 

basaltic (< 50% Si0 2 

) to form what could be considered 

average continental crust. A number of different hypotheses 

have been put forward, including a marked change in plate 

tectonics since the early Archean, and various forms of 

chemical refining in island arcs or in continental arcs such 

as the Andes and Sierra Nevada, followed by delamination 

of a restite layer from the base of the crust along with mantle 

lithosphere. In addition to direct studies of the cratons, 

a number of experiments are examining formation and 

evolution of the continental crust as an arc process. These 

projects include controlled- and passive-source experiments 

in several island arc settings, including the Marianas, the 

southeastern Caribbean, and the Aleutians, complemented 

by studies of the continental arc process in the Andes and 

Figure 7. Summary figure from the Kaapvaal project in southern Africa 

showing geological provinces (top) with PASSCAL broadband seismograph 

stations (black dots). Kimberlite pipes are shown schematically 

from diamondiferous kimberlite localities showing their relationship to 

crustal and mantle seismic structure. The Moho is shown as a gridded 

surface at center. At the bottom are Vp velocity perturbations in the 

upper mantle, shown as a constant blue for anomalies > 0.45% and 

constant red for anomalies < -0.7. Inferred tectospheric roots of the 

Kaapvaal and Zimbabwe cratons are outlined in blue. (From James et 

al., 2001) 

Figure 8. (top) CCP stacked receiver function image of the Proterozoic 

Abitibi-Grenville boundary showing an offset Moho. (bottom) 

Scattered wave inversion of the same data set show velocity perturbations 

and more clearly delineate subduction-collision structures in the 

Moho. (From Rondenay et al., 2005) 

10

Sierra Nevada. Suspected delamination 

phenomena have been investigated by 

several PASSCAL-supported experiments, 

including in Arctic Alaska, the Sierra 

Nevada, the Wallowa Mountains, the 

eastern Rio Grande rift, and the Vrancea 

zone, Romania. 

The Core 

Improved global coverage afforded by 

PASSCAL experiments has proven important 

for core studies, giving seismologists 

new vantage points for viewing core 

phases across relatively dense seismograph 

arrays. Data from the Kaapvaal craton 

were used to discover that the edges of 

South African deep mantle low-velocity 

anomalies are very sharp, leading to a 

consensus that they arise from a combination 

of thermal and chemical perturbations. Data from the 

PASSCAL MOMA, FLED, RISTRA, and other US arrays 

have led to identification of core-mantle boundary anomalies 

under the western Caribbean plate that have various interpretations, 

including D’’ “slab graveyard” sites. As an example 

of serendipitous discovery, data from the BOLIVAR array 

in Venezuela displayed a previously undetected retrograde 

seismic phase, PKIIKP2, indicating that Earth’s center has a 

unique seismic structure (Niu and Chen, in review; Figure 9). 

177.0 o 

177.5 o 

Epicentral Distance 

178.5 o 

178.0 o 

179.0 o 

179.5 o 

06/06/2004 579 km 5.9 Mw 

PKIKP 

PKIIKP1 

PKIIKP2 

-10 0 10 20 30 40 50 60 

Time relative to PKIKP (s) 

Figure 9. (left) Bolivar array recording of an earthquake from the antipode displaying the 

major arc phase PKIIKP2. (top right) Ray paths for the minor arc phase PKIIKP1 and major 

arc phases PKIIKP2. Slowness-time stack for all antipode earthquakes recorded by the 

Bolivar array showing the PKIIKP phases. (From Niu and Chen, in review) 

Slowness relative to PKIKP (s/ o ) 

3.0 

2.0 

1.0 

0.0 

-1.0 

-2.0 

-3.0 

PKIKP 

Currently and recently deployed PASSCAL arrays in 

Antarctica (see Polar Efforts section) are expected to provide 

valuable information on inner core anisotropy by providing 

the first set of dense measurements made along paths nearly 

parallel to Earth’s rotational axis. These measurements are key 

to deciphering the anisotropic structure of the inner core, and 

CMB 

its pronounced east-west hemispherical asymmetry. 

ICB 

PKPab 

PKIKP 

PKIIKP2 

PKIIKP1 

PKIIKP1? 

0 20 40 

Time relative to PKIKP (s) 

PKIIKP2 

178 o 

60 

-150 -50 -40 -30 -20 -10 0 

High-Resolution Seismology 

In contrast to large-scale experiments that commonly pursue 

the great themes of Earth evolution, many high-resolution 

seismology projects have more pragmatic motivations. For 

instance, high-resolution seismology is an important tool for 

assessing groundwater resources as we grapple with locating, 

characterizing, and protecting water sources for an increasingly 

urbanized society. Seismic investigations have proven 

particularly valuable in the arid southwestern United States 

where deep aquifers, often occupying tectonically controlled 

basins, are a crucial source of drinking, agricultural, and 

industrial water. Aquifer assessment commonly requires 

signal penetration of no more than 1–2 km. 

High-resolution seismology has proven to be one of several 

useful tools for delineating likely locations of contaminants 

deliberately or inadvertently lost to the subsurface. Away 

from the pollution-discharge point, seismic imaging can 

identify channels along which contaminants migrate and 

traps in which they pond. Such subsurface characterization 

of contaminant traps is critical information for the hydrologists 

and engineers designing successful surfactant flooding 

and pump-and-treat remediation programs. Surveying for 

contaminants frequently requires ultra-high-resolution seismology 

(sampling rates ~1 kHz or more), with targets often 

found as shallow as 10 m and resolution required at scales 

11

of tens of centimeters. PASSCAL multichannel systems and 

TEXAN instruments have been deployed in this manner 

for two- and three-dimensional surveys at a number of 

contaminant sites. 

PASSCAL high-resolution equipment also has an important 

educational use. High-resolution reflection and refraction 

experiments are ideally suited for teaching seismology 

fundamentals in exercises that are inexpensive and easy to 

conduct with student assistance. PASSCAL equipment has 

seen enormous class use for field geophysics classes, exploration 

geophysics courses, and has also been used by the NSF 

Research Experience for Undergraduates IRIS Internship 

Program and by the Summer of Applied Geophysical 

Experience (SAGE) geophysical field camp coordinated with 

Department of Energy and other partners. High-resolution 

instrumentation can be used to introduce and reinforce 

a number of important seismology concepts, including 

basic principles of wave propagation (reflection, refraction, 

surface waves); the power of seismic arrays for detecting 

weak signals; the strengths, limitations, and differences 

between imaging Earth structure with scattered waves and 

transmitted waves; and the importance of record keeping 

and quality control during data acquisition to successfully 

process seismic data. 

Earthquakes and Earthquake Hazards 

PASSCAL instrumentation has been used extensively 

for the study of earthquake sources and for earthquake 

hazards research and assessment in urban 

areas. Earthquake source studies using PASSCAL 

instrumentation include RAMP (Rapid Array 

Mobilization Program) deployments for determining 

aftershocks, controlled-source experiments and fault 

zone guided-wave studies to understand the structure 

of fault zones, and recent array studies of episodic 

tremor and slip (ETS) in Cascadia. 

PASSCAL RAMP consists of 10 six-channel instruments 

with strong-motion-capable sensors, reserved 

for rapid mobilization to record seismicity following 

an earthquake or associated with a volcanic eruption. 

RAMP instruments were used to monitor aftershocks 

following major shocks in: 1989 at Loma Prieta, 

CA; 1992 at Little Skull Mountain, NV; 1992 at 

Landers and Mendocino, CA; New Guinea in 1996; 

Pennsylvania in 1998; Ohio and Nisqually, WA in 

2001; Mexico in 2001; and Puerto Plata, Dominican 

Republic in 2003. 

A frequent use of PASSCAL’s high-resolution seismic 

equipment has been for imaging the shallow structure 

of active faults (Figure 10). Motivated by improving 

hazard awareness, such studies have been progres- 

DEPTH (km) 

SW 

0.0 

-0.5 

MSL 

-1.0 

SW 

0.0 

0.5 

MSL 

1.0 

SW 

0.0 

0.5 

MSL 

1.0 

VELOCITY (km/s) 

2.0 2.4 2.8 3.2 3.6 4.0 

A 

B 

C 

2 

4 

3 

SAF 

GHF 

-3 -2 -1 0 1 

-3 -2 -1 0 1 

-3 -2 -1 0 1 

DISTANCE (km) 

Figure 10: Tomographic and seismic reflection image of the near-vertical 

San Andreas and Gold Hill faults near the SAFOD drill hole (derrick) 

at Parkfield, CA. The acquisition used 840 channels of high-resolution 

seismic equipment, including the PASSCAL multichannel systems. (After 

Hole et al., 2001) 

nF 

nF 

nF 

SAF 

GHF 

SAF 

GHF 

NE 

NE 

NE 

12

Figure 11: High-resolution seismic reflection profile from urban Los 

Angeles showing shallow folding above the backlimb of the Compton 

blind thrust fault. The profile shows a narrow “kink band” above 

the location where a thrust ramp leaves a horizontal basal fault. 

Kinematic model is shown at top. Yellow lines show the locations 

of cores used to obtain ages and measure the thickness of the shallow 

strata, from which slip rates can be estimated. (Modified from 

Leon et al., submitted) 

sively moving into more urbanized areas as the number of 

available channels and quality of shallow seismic sources has 

increased. In addition to imaging the faults themselves, these 

studies have been imaging the shallow folds above deep 

“blind” thrust faults that lie kilometers below the surface, 

helping assess risks from faults which do not have a surface 

rupture (Figure 11). 

Figure 12. Ground shaking over the sediment-filled Seattle basin 

resulting from teleseismic signals from the 1999 Chi-Chi, Taiwan, 

earthquake, and during local earthquakes and blasts, as measured 

using PASSCAL instruments. The tomographic image of the basin was 

made using over 1000 seismometers that recorded large blasts. (Figure 

from Pratt et al., 2003 and Snelson et al., 2007) 

The availability of large numbers of instruments allows determination 

of the spatial distribution of strong-motion amplification 

and duration caused by the excitation of shallow sedimentary 

basins and deeper structures during earthquakes. 

In the Puget Sound region, for example, large numbers of 

PASSCAL sensors have been used to monitor ground shaking 

created by teleseismic and local earthquakes, large blasts, and 

even during the demolition of the King Dome sports stadium 

(Snelson et al., 2007; Figure 12). Similar studies have been 

carried out in Anchorage, Alaska, and Hawaii to map seismic 

amplification beneath urban areas. 

PASSCAL high-resolution seismic equipment also is used for 

geotechnical studies to characterize the shallow subsurface. 

In particular, measurements of the shallow S-wave velocity 

structure, either through small-scale refraction profiles or 

measurement of surface wave speeds via ambient noise analysis, 

are used to determine amplification factors to estimate 

damage likelihoods from shear waves during earthquakes. 

For example, one recent study mapped the shallow S-wave 

velocities along profiles in the Reno and Las Vegas, Nevada, 

urban areas, and in Los Angeles. 

13

Nuclear Explosion Seismology 

Nuclear explosion monitoring research is focused on lowmagnitude 

events (m b 

≤ 4.0) over broad areas, particularly 

in Eurasia. Monitoring normally requires observations of 

events at regional distances (< 1500 km) where signals are 

best observed at relatively high frequencies (0.05–10 Hz). 

Propagation through the heterogeneous crust and upper 

mantle has a strong impact on these signals, and requires 

calibration to account for path-specific seismic observables 

(e.g., travel times, amplitudes, surface wave dispersion, 

and regional phase propagation characteristics). The 

PASSCAL facility provides instrumentation for research 

experiments related to nuclear monitoring, as well as an 

archived global data set that indirectly supports nuclear 

explosion monitoring research by constraining crust-mantle 

structural models, particularly in the critical Eurasian 

region, and by improving empirical calibration methods. 

Specific experiments that have contributed to our knowledge 

of seismic structure and seismic monitoring calibration 

include: 1991–1992 Tibet (Owens et al., 1993), Tanzania 

(Nyblade et al., 1996), INDEPTH-II (Nelson et al., 1996), 

1995–1997 Saudi Arabia (Vernon and Berger, 1998), Eastern 

Turkey Seismic Experiment (Sandvol et al., 2003), and Iraq 

(Ghalib et al., 2006). The value of archived PASSCAL data is 

illustrated here; although these experiments were generally 

supported to address fundamental scientific objectives, they 

nonetheless provide data that benefit applied seismology 

for nuclear monitoring. 

Underground nuclear explosion monitoring is the main 

theme of verification research, but source phenomenology is 

a second important area of interest. In this vein, PASSCAL 

instrumentation has been used in experiments with the 

specific goal of improving understanding of large chemical 

explosions, such as the nuclear analog Non-Proliferation 

Experiment (Zucca, 1993; Tinker and Wallace, 1997), as well 

as the Source Phenomenology Experiment, which examined 

mining explosions (Leidig et al., 2005; Hooper et al., 2006). 

Polar Efforts 

Seismology in polar regions is a rapidly developing component 

of PASSCAL-supported science. Antarctic, Greenland, 

and past continental ice sheets and sea ice have dramatically 

affected climate and sea level throughout Earth’s history. Yet, 

great extents of these key regions are largely inaccessible 

to geologic study, and Antarctica remains a tectonic terra 

incognita. IRIS PASSCAL-supported seismology, principally 

funded by the NSF Office of Polar Programs (OPP), is 

enhancing fundamental understanding of basic crustal and 

upper mantle structure as a part of larger interdisciplinary 

studies, and is being used in novel studies of ice cap, glacial, 

and iceberg-related seismic phenomena. Facility support for 

these efforts requires significant new development efforts in 

sensor, telemetry, and station design. Currently, this effort 

is being accomplished through a joint IRIS PASSCAL/ 

UNAVCO OPP Major Research Instrumentation (MRI) 

initiative, supplemented by a second IRIS MRI largely for 

equipment procurement. 

The far polar regions have the poorest seismographic 

coverage of any region on Earth, and temporary PASSCAL 

deployments at high latitudes not only provide regional 

structure but also unique raypaths for constraining important 

elements of deep structure in global tomographic models. 

Broadband seismic recording in polar regions is uniquely 

useful for constraining inner core anisotropy, because the 

axis of inner core anisotropy is oriented approximately 

parallel to Earth’s spin axis. The source of the anisotropy is 

believed to be the preferred orientation of anisotropic inner 

core iron crystals, but alignment mechanisms and crystallography 

are unclear. Improved understanding the inner core is 

key to understanding the evolution of the core system, core 

heat flow, and magnetic field throughout Earth history. 

A series of completed and ongoing PASSCAL experiments 

(e.g., Figure 13) is interrogating the seismic structure of 

the Antarctic lithosphere using specialized cold-weather 

instrumentation. Little has been known about the origin 

14

history of these highlands is of significant interest because 

the first glaciation of the Cenozoic nucleated here ~ 34 Ma. 

There are numerous proposed mechanisms for the origin of 

the highlands, including collisional tectonics, extensional 

tectonics, mantle plume (hotspot) processes, underplating 

and/or retrograde metamorphism of eclogite, dynamic 

support by mantle convection, and erosional isolation of 

an elevated region protected from denudation by resistant 

cap rocks. The plume hypotheses are particularly intriguing 

because of the potential for abnormal geothermal inputs to 

the bases of glaciers and ice sheets, which affect their coupling 

to Earth, the formation of subglacial lakes, and their 

long-term stability. 

Figure 13. Ongoing POLENET PASSCAL broadband 

seismograph/GPS deployment relative to bedrock 

topography and tectonic features. WARS=West Antarctic 

rift system; TAM=Transantarctic Mountains. Dotted 

lines: crustal block boundaries (black) AP=Antarctic 

Peninsula; TI=Thurston Island; MBL=Marie Byrd Land; 

EWM=Ellsworth-Whitmore Mtns]. POLENET has been 

funded by NSF OPP during the International Polar Year 

period. POLENET, and an East Antarctica project AGAP, 

are initial beneficiaries of recent PASSCAL polar instrumentation 

developments. (From Lythe et al., 2001) 

and timing of major mountain uplifts in the highlands of 

West Antarctica. The West Antarctic Rift System (WARS) 

is one of the largest regions of diffuse continental extension 

in the world, perhaps comparable to the western US Basin 

and Range, but the pattern of rifting and geologic history 

of WARS rift basins are virtually unknown. East Antarctica 

is characterized by the highest mean deglaciated elevation 

of any major continental region. The uplift mechanism and 

PASSCAL experiments are providing novel and important 

information on processes affecting glaciers, ice streams, and 

sea ice, frequently in consort with GPS, weather stations, icepenetrating 

radar, and other glaciological instrumentation 

(Figure 14). For example, the dynamics of outlet glaciers, 

ice shelves, and ice streams are of principal importance for 

understanding the stability of large continental ice sheets 

and the impacts of possible climate change. PASSCALfacilitated 

studies of seismicity associated with the flow of 

ice streams and some mountain glaciers have advanced 

understanding of, in many cases unanticipated, relationships 

between small external forcings (tidal, ocean swell, and possibly 

even smaller atmospheric pressure forcings; Figure 15) 

and cryosphere dynamics. PASSCAL seismographs have 

further been used as a principal component of multidisciplinary 

studies of interrelated glaciological, atmospheric, 

and oceanographic processes affecting giant tabular icebergs 

Icesheet-Climate Model Archean Craton Proterozoic Mobile Belts 

AFRICA 

INDIA 

East African Orogen 

6 50-550 M a 

AFRICA 

INDIA 

GSM 

Pinjarra Orogen 

600-500 Ma 

WI 

1330-1130 MA 

AUSTRALIA 

Archean 

Proterozoic 

AUSTRALIA 

EAST ANTARCTICA 

East Antarctica Ice Sheet 

Proterozoic 

-Paleozoic 

Figure 14. (left) Coupled ice sheet-climate model showing ice elevation 5 My following an increase in global CO 2 

about 35 Ma. The first glaciation 

in the cooling world localize over the Gamburtsev Mountains (site of the ongoing AGAP project). (center and right) Speculative tectonic structure 

of Antarctica. The geology of East Antarctica is presently unknown, so the history and uplift mechanism of its internal highlands is uncertain. East 

Antarctica may be comprised of a single Archean craton or multiple cratons. (Figure from DeConto and Pollard, 2003) 

15

West Antarctic Ice Stream Velocity from INSAR 

Whillans Ice Stream Velocity from GPS 

Regional distance Rayleigh waves from Whillans Slip 

Figure 15. (left) West Antarctic Ice Stream average velocities from INSAR (Joughin and Tulaczyk, 2002). (middle) The Whillans Ice Stream 

shows stick-slip behavior, with slip episodes requiring approximately 10–15 minutes to propagate from the nucleation point to the grounding 

line (data from the TIDES project, courtesy of S. Anandakrishnan). (right) Rayleigh waves excited by these slip events were detected—1100 km 

away at the PASSCAL TAMSEIS array, suggesting such behavior can be routinely monitored seismically with broadband instrumentation. 

(From Wiens et al., 2006) 

calved from the Ross Ice Shelf since 2000, including calving, 

breakup, and collision mechanisms producing tremor 

signals visible at teleseismic distances as oceanic T phases 

(Figure 16). Interest in seismic recordings of glaciological 

processes has been substantial, and over the past several 

years the number of polar PASSCAL experiments related to 

glaciology has exceeded the number with purely solid-Earth 

motivations. PASSCAL and associated longer-term seismic 

deployments in and around Ross Island and Mount Erebus 

volcano, as well as on the surfaces of large, recently calved 

megaicebergs, have identified a host of novel seismological 

and acoustic ice-ice and ice-seabed collision signals associated 

with the birth and evolution of Earth’s largest freely 

floating ice masses. 

Recently, Ekstrom et al. (2003) discovered a class of large 

(M w 

~ 5) long-period seismic sources from the periphery 

of Greenland that generate long-period seismic waves 

equivalent to those produced by magnitude-5 earthquakes, 

but no detectable high-frequency body waves. Although 

similar events are observed in Alaska and Antarctica, more 

than 95% are associated with Greenland outlet glaciers 

February 3, 2001, 00:00.00 UTC 

16 

Vertical Displacement Frequency (Hz) 

12 

8 

4 

0 

0 500 1000 1500 2000 2500 3000 3500 

Time (s) 

Figure 16. Megaiceberg tremor recorded at PASSCAL TAMSEIS, GSN, and Mount Erebus seismic stations (record section at left.) Note the 

exceptional duration of the seismic source (over 1 hr) and its regional visibility more than 300 km into the east Antarctic plateau. The complex 

and evolving spectral structure of this B15 iceberg-Ross Island collision (spectrogram at right) arises from tens of thousands of repetitive stick-slip 

subevents occurring during ice-ice or ice-ground collisions. (From MacAyeal et al., in prep.) 

16

(Figure 17). The seasonal signal and temporal 

increase apparent in these results are consistent 

with a dynamic response to climate warming 

driven by an increase in surface melting and to 

the supply of meltwater to the glacier base, which 

affects transport and calving in these very large 

and relatively warm glacial systems. In January 

2008, IRIS and NMT submitted a proposal to the 

NSF MRI program, “Development of a Greenland 

Ice Sheet Monitoring Network (GLISN),” specifically 

to improve the monitoring of Greenland 

seismicity, with particular attention to seismicity 

that may be associated with climate change affecting 

on the icecap and its outlet glaciers. 

Figure 17. (A) Topographic map of Greenland with locations of 136 glacial 

earthquakes (red circles): DJG, Daugard Jensen Glacier; KG, Kangerdlugssuaq 

Glacier; HG, Helheim Glacier; SG, southeast Greenland glaciers; JI, 

Jakobshavn Isbrae; RI, Rinks Isbrae; NG, northwest Greenland glaciers. 

(B) Histogram showing seasonality of Greenland glacial earthquakes. Green 

bars show the number of detected glacial earthquakes in each month, and 

gray bars show the earthquakes of similar magnitude detected elsewhere north 

of 45 N. C: Histogram showing the increasing number of glacial earthquakes 

(green bars). (From Ekstrom et al., 2006) 

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18

Program History 

PASSCAL Instrument Center, 

Socorro, NM. 

Warehouse forklift and 

packing area. 

Sensors on rack in the 

warehouse. 

Sensor repair bench. 

Cable storage system. 

In the early 1980s, seismologists formed the Program for 

Array Seismic Studies of the Continental Lithosphere to 

develop a portable array seismograph facility. PASSCAL 

was subsequently merged with another group endeavoring 

to develop a modern global seismic network; the resultant 

collaboration became the IRIS Consortium. PASSCAL’s goals 

were to develop, acquire, and maintain a new generation 

of portable instruments for seismic studies of the crust and 

lithosphere, with an initial goal for instrumentation set 

at a somewhat arbitrary number of 6000 data-acquisition 

channels. PASSCAL formed the flexible complement (the 

“Mobile Array” in the 1984 IRIS proposal to NSF) to the 

permanent GSN observatories. During the first cooperative 

agreement between IRIS and NSF (1984–1990), the primary 

emphasis was on the careful specification of the design goals 

and the development and testing of what became the initial 

six-channel PASSCAL instruments. Three technological 

developments between 1985 and 1995 were critical to the 

success of portable array seismology: the development of 

low-power, portable broadband force-feedback sensors; 

the availability of highly accurate GPS absolute-time-base 

clocks; and the advent of compact, high-capacity hard disks. 

An initial purchase of 35 seismic systems were delivered in 

1989 and maintained through the first PASSCAL Instrument 

Center at Lamont-Doherty Geological Observatory of 

Columbia University. During the second cooperative agreement 

(1990–1995), the PASSCAL instrument base at the 

Lamont facility, which focused on the broadband sensors 

used primarily in passive-source experiments, grew to more 

than 100 instruments. 

In 1991, a second PASSCAL Instrument Center was established 

at Stanford University to support a new three-channel 

instrument that was designed for use in active-source 

experiments and for rapid deployment for earthquake 

aftershock studies. By 1995, almost 300 of these instruments 

were available at the Stanford facility. The rationale for the 

Stanford Instrument Center was in part driven by proximity 

to the USGS Menlo Park Crustal Studies Group, which was 

maintaining a fleet of 200 Seismic Group Recorders (SGRs) 

that were widely used in the controlled-source community. 

The SGRs were donated to Stanford by AMOCO, reconditioned 

for crustal studies, and maintained by the USGS with 

support from PASSCAL. Newer-generation TEXANs were 

developed by Refraction Technologies, Incorporated (REF 

TEK), UTEP, the University of Texas at Dallas (UTD), and 

Rice using funds available through the state of Texas. Initial 

instrument procurement began in 1999 and the aging SGRs 

were gradually decommissioned over a period of three years. 

In 1998, the instrument centers merged and moved to the 

current PASSCAL Instrument Center (PIC) at the New 

Mexico Institute of Mining and Technology in Socorro, NM 

(Figure 18). The consolidation and move were motivated by 

a number of considerations, principally: (1) the desire for 

greater technological synergy and coordination within the 

facility, (2) the cost savings of operating a single instrument 

center, and (3) the need for greater operational space. New 

Mexico Tech facilitated construction of a new, custom- 

19

Main 

Entrance 

107'-6" 

Offices 

Foyer 1 

North Entrance 

Offices 

61'-3" 

Offices 

Lab 1 

RR 

RR Pier 1 

Computer 

Lab 1 

Offices 

Patio 2 

Foyer 2 

143'-2 1/2" 

RR 

Offices 

Lab 2 

RR 

Break 

Rm. 

Break 

Rm. 

Patio 1 

RR 

RR 

Whse. 

Office 

Mechanical Yard 

Lab 3 

Conference 

Rm. 1 

Offices 

Patio 3 

Conf. Rm. 

2 

Computer 

Lab 2 

Pier 2 

Garage 

Door 

Mechanical Yard 

Offices 

138'-0" 

designed facility, with 7500 sq. ft. of office and lab space 

and 20,000 sq. ft. of warehouse space. This complex was 

later expanded to accommodate USArray operations, adding 

an additional 11,000 sq. ft. of office and lab space. The 

building was designed by the PASSCAL technical staff and 

NMT to optimize PIC operations. Land and construction 

funds to build the original facility building and USArray 

addition were entirely provided by the state of New Mexico 

through the university. 

Starting in 2002, the Department of Energy (DOE) provided 

funds to replace the original six-channel and three-channel 

data acquisition systems (DASs), which were becoming aged 

and failure prone, with modern systems. The new DASs, 

produced by REF TEK and Kinemetrics/Quanterra, incorporate 

the latest technologies from the computer industry, 

and as a consequence, require much less power, have higher 

recording capacity than the first-generation instruments, use 

modern memory components, and are configured to operate 

with a number of communication systems as either serial 

devices or TCPIP nodes. The preceding REF TEK 72a series 

recorders have been officially retired from use. However, IRIS 

and REF TEK are presently making these retired instruments 

available to international partner institutions seeking to 

establish or upgrade their permanent networks. 

273'-9" 

Warehouse 

Garage 

Door 

MRO 

Figure 18. IRIS-PASSCAL Instrument Center, 

New Mexico Tech, Socorro, New Mexico. 

71'-5 7/16" 

Office Space = 

1,146 sq. ft. 

Computer Lab Space = 1,316 sq. ft. 

Lab Space = 

3,724 sq. ft. 

Warehouse Space = 17,912 sq. ft. 

A major enhancement to US seismological resources and 

increased activities at the PIC began in 2003 with the start 

of EarthScope, a continent-scale, multidisciplinary project 

funded under the NSF Major Research Equipment and 

Facility Construction account. IRIS is responsible for the 

operation of USArray, the seismological component of 

EarthScope. With separate funding through EarthScope, 

a Flexible Array, providing both broadband and high-frequency 

instruments for individual PI experiments, operates 

out of the PASSCAL instrument Center. Most Flexible Array 

operational needs and procedures closely parallel those of 

the core PASSCAL program. The largest part of USArray, the 

400-element Transportable Array that will gradually cross 

the conterminous United States and Alaska continent over 

a 15-year period, is based on many of the technologies and 

operational procedures developed by PASSCAL. A USArray 

Array Operations Facility (AOF) at the PIC (funded through 

a separate subaward to New Mexico Tech) supports the operation 

of both the Flexible Array and the Transportable Array. 

The AOF shares personnel and logistic support with the 

core PASSCAL program, leading to significant leverage and 

efficiencies for both programs. The AOF also acquires, tests, 

and assembles primary field Transportable Array components. 

A Transportable Array Coordinating Office (TACO), 

located at the PASSCAL Instrument Center, but staffed and 

operated as an independent USArray unit, is responsible for 

many of the specialized logistic and siting activities required 

in the operation of the Transportable Array. With EarthScope 

support, a remote backup for the IRIS DMC archive has been 

established at the PIC; office space is provided for a USArray 

data analyst and two UNAVCO employees who provide quality 

control for EarthScope PBO strain data. 

20

Timeline 

1984 ............... IRIS incorporated 

1985 ............... Start instrument development 

1986 ............... Ouachita Experiment (1 st IRIS sponsored experiment) 

1986 ............... Basin & Range Active Experiment 

1986 ............... Issue RFP for new instrument 

1987 ............... Issue contract to develop a new instrument 

1988 ............... REF TEK delivers first 10 prototype instruments 

1988 ............... Basin & Range Passive Experiment 

(1 st experiment with prototype instruments) 

1989 ............... Delivery of first 35 production instruments 

1989 ............... Open first instrument center at Lamont 

1989 ............... Greenland Experiment (1 st experiment with production 

instruments, 1 st onshore/offshore experiment) 

1989 ............... Loma Prieta (1 st aftershock experiment ) 

1990 ............... Brooks Range (1 st large active source experiment). 

1990 ............... Receive first broadband sensors 

1990 ............... SAMSON (1 st experiment with broadband sensors) 

1990 ............... Development of three-channel instrument 

1990 ............... SERIS (1 st deployment to Antarctica) 

1991 ............... Received first three-channel instruments 

1991 ............... Instrument center at Stanford established 

1991 ............... Tibet (1 st large broadband experiment to produce SEED data) 

1993 ............... Cascadia (1 st broadband experiment with high station density) 

1993 ............... DOE funds Geometrics instruments for high-resolution imaging 

1993 ............... REF TEKs upgraded with 24-bit digitizers 

1995 ............... Acquisition of first GPS clocks for REF TEKs 

1997 ............... Issued community-wide RFP for instrument center 

1998 ............... Test of broadband array in Colorado 

1998 ............... Established PASSCAL Instrument Center at New Mexico Tech, 

closed LDEO and Stanford instrument centers 

1998 ............... Issued RFP for new type of data acquisition system 

1999 ............... First TEXAN instruments delivered to UTEP, funded by State of Texas 

1999 ............... CDROM refraction: First large experiment to use TEXANs 

1999 ............... Kaapvaal experiment: First experiment with over 50 broadband stations 

1999 ............... Broadband array deployed to Kaapvaal 

1999 ............... LARSE II first deployment of > 1000 instruments in metropolitan area 

2000 ............... First TEXAN instruments delivered to PASSCAL 

2000 ............... TAMSEIS (1 st large broadband experiment in Antarctica) 

2002 ............... First DOE money received to purchase new data acquisition system 

2002 ............... Hi Climb (1 st experiment with 75 broadband stations) 

2003 ............... USArray starts, construction of additional space at NMT 

2005 ............... Phase out of old data acquisitions system begins 

2007 ............... High Lava Plains Experiment fields first 100-instrument 

broadband experiment 

21 

Tibet. Transporting equipment 

in the field. 

Alaska. STEEP experiment. 

Utah, Hill AFB. High resolution 

imaging using TEXANs. 

Venezuela. Transporting gear. 

Mt. Erebus, Antarctica.

Instrumentation 

The 1984 IRIS proposal to NSF (the “Rainbow Proposal”) 

estimated that about 1000 instruments with 6000 recording 

channels would be needed to support modern field programs 

in seismology. The size and composition of the PASSCAL 

inventory has evolved through a continuing reassessment 

of the balance between technical and scientific pressures. A 

current instrument inventory is provided in Table 1. 

Although standardization of equipment, data formats, and 

operational procedures is an essential ingredient in the 

success of all IRIS programs, PASSCAL has had to handle 

special challenges and trade-offs as experiment designs 

have evolved as a result of changing scientific interests. 

The wide variety of experimental configurations supported 

by PASSCAL, and the need for performance optimization 

under extreme field conditions, have led PASSCAL 

to develop a number of “standardized” field systems 

(Figure 19). For recording earthquakes, PASSCAL offers selfcontained, 

short-period and broadband instruments, and 

telemetered broadband arrays. For active-source seismology, 

PASSCAL offers single-channel TEXAN reflection/refraction 

instruments, three-component short-period instruments, 

and multichannel cabled instruments for high-resolution, 

usually shallow, seismology. 

REF TEK developed the first PASSCAL data acquisition 

system under contract to IRIS. This RFP approach to 

development allowed IRIS to purchase equipment built to 

specifications that was optimized for PASSCAL use. After 

initial instrument development, PASSCAL continues to 

work with the manufacturers to improve the equipment 

and add capabilities that are driven by community needs. 

A close working relationship with manufacturers entails 

collaborative testing of prototypes and sometimes paying 

for delivery of prototype instruments. This collaboration 

with manufacturers results in equipment that is nearer to 

our desired specifications and is cheaper to develop for 

PASSCAL because the manufacturer underwrites part of the 

development with an eye to the broader market. Almost all 

of the second-generation acquisition systems and sensors in 

use today have resulted from this sort collaboration. 

Long-Term Passive Deployments 

Short-Period and Broadband Instruments 

Much of PASSCAL’s efforts center around fielding long-term 

deployments of up to 100 broadband stations for recording 

teleseismic, regional, and local earthquakes. These 

experiments are designed by individuals or small groups of 

investigators, usually funded by NSF or DOE, who target 

Earth structures from the crust to the inner core (see Box 1). 

Frequent motivations include structural seismology investigations 

and study of earthquake aftershocks, fault-zoneproperties, 

and active volcanoes. 

PASSCAL instruments now used for passive experiments are 

either three-channel REF TEK RT130s or Quanterra Q330s, 

typically coupled with broadband or intermediate-period 

sensors with long-period response extending to 120 or 30 s, 

respectively. Most stations are installed in a stand-alone 

mode away from commercial power or communications, 

and rely on solar power systems and local disks to record 

data. 

Although each portable PASSCAL network deployment is 

motivated by a specific research experiment, the combined 

effect of multiple experiments around the world is to effectively 

provide temporary, high-spatial-density augmentation 

22

Multichannel Equipment 

Cable with 

Sensor Takeouts 

Intermediate & Short Period Equipment 

Intermediate Period Sensors (40 sec) 

High Frequency Vertical Sensor 

Short Period Sensors (2 Hz) 

Trigger System Reel 

Short Period Sensor (4.5 Hz) 

24 Channel 

Data Acquisition System 

Power Distribution Controller 

Data Acquisition System 

Solar Power System 

Figure 19. PASSCAL major equipment. Instrumentation provided and supported by the PASSCAL facility can be divided 

into four categories: active source, passive source broadband, intermediate and short period, and multichannel. 

23

Table 1: PASSCAL Instrument Inventory (2/20/2007) 

DATA ACQUISITION SYSTEMS 

HIGH RESOLUTION 

PASSCAL 

Quanterra Q330, 3 Channel 381 

REF TEK RT130, 3 Channel 445 

REF TEK RT130, 6 Channel (RAMP) 10 

USArray Flexible Array 

REF TEK RT130, 3 Channel 407 


USArray Transportable Array 


Polar 


TOTAL HIGH RESOLUTION 1756 

TEXANS 

PASSCAL 

REF TEK RT125, 32 MB 89 

REF TEK RT125, 64 MB 204 

REF TEK RT125A, 256 MB 249 


REF TEK RT125A, 256 MB 1700 

UTEP 

REF TEK RT125A, 256 MB 440 

TOTAL TEXANS 2682 

CABLE RECORDING CHANNELS 

Geometrics Multichannel, 60 Channel 4 x 60 = 240 

Geometrics Geode, 24 Channel 8 x 24 = 192 

Polar 

Ice Streamer, 60 Channel 1 x 60 = 60 

TOTAL CABLE RECORDING CHANNELS 492 

SENSORS 

BROADBAND 

PASSCAL 

Streckheisen STS2 (120 sec) 219 

Guralp CMG 3T (120 sec) 216 

Trillium 240 (240 sec) 3 



USArray Transportable Array 

Streckheisen ST2 (120 sec) 251 



Polar 


Guralp CMG3T (120 sec) 17 

TOTAL BROADBAND 1272 

INTERMEDIATE TO SHORT PERIOD 

PASSCAL 

Guralp CMG3 ESP (30 sec) 56 



Trillium 40 (40 sec) RAMP 10 



TOTAL INTERMEDIATE TO SHORT PERIOD 264 

HIGH FREQUENCY 

Mark Products L22 ( 2 Hz), 3 comp 168 

Mark Products L28 (4.5 Hz), 3 comp 406 

Geospace HS1 (2 Hz), 3 comp 21 

Teledyne S13, 1 comp 35 

TOTAL HIGH FREQUENCY 630 

STRONG MOTION 

Kinemetrics Episensor Accelerometer, 3 comp 10 

Terra Tech Accelerometer, 3 comp 11 

TOTAL STRONG MOTION 21 

24

Box 1. Anatomy of a PASSCAL Experiment 

Typical interactions between most PIs and the PASSCAL 

facility during experiment planning and implementation 

involve 10 key steps. 

Step 1: Planning 

Individually or collaboratively, PIs motivated by a scientific 

question plan an experiment requiring instruments 

provided by the PASSCAL facility. At this stage, the facility 

often provides a deployment strategy that will be part of the 

proposal to a funding agency. It also supplies information 

for budgets (e.g., shipping costs). An estimate of the equipment 

schedule can also be provided at this time. 

Step 2: Requesting Instruments 

The PI places a request for the instruments through the 

online request form (http://www.passcal.nmt.edu/forms/ 

request.html). Typically, instruments are requested as the 

proposals are submitted to the funding agency. This step 

ensures an early spot in the queue once the project is 

funded. 

Step 3: Funding Notification 

When the PIs learn that their project will be supported, 

PASSCAL is notified and the experiment is officially scheduled. 

In case of schedule conflicts, a priority system exists 

where NSF and DOE projects share the same high-priority 

level. Most active-source experiments can be scheduled 

within a year of funding, whereas broadband deployments 

have a waiting period of up to 2.5 years. 

Step 4: Training and Logistics Meeting at the Facility 

Users are required to visit the PASSCAL facility for a 

briefing on logistics, and training on equipment use. A 

complete list of all needed equipment and a shipping plan 

are generated. 

Step 5: Shipment Preparation 

Equipment IDs are scanned, the equipment packed into 

rugged cases and, for larger experiments, placed on pallets. 

The facility helps the PI to generate shipping documents 

and arrange for shipment. In the case of international 

experiments, assistance in providing the needed contacts 

and letters for customs is provided to the investigator. 

Step 6: In-Field Training and Huddle Testing 

On site, PASSCAL provides additional instrument training 

for experiment participants. PASSCAL personnel perform a 

function test “huddle” and attempt to repair any equipment 

that was damaged during transport. 

Step 7: Assisting with Deployment 

For active-source experiments, PASSCAL engineers stay 

with the equipment for the duration of the experiment. 

They are responsible for all instrument programming and 

data offloading, with substantial help from experiment 

participants. For broadband and short-period type experiments, 

PASSCAL support usually is limited to the huddle 

test, initial station deployment, and perhaps the first data 

service run. The goal is to have equipment in good working 

order and to have fully trained investigators operating the 

equipment. 

Step 8: Service and Maintenance 

A typical service cycle for broadband and short-period 

stations is an interval of about three months. While in the 

field, if any equipment fails or needs repair, the PASSCAL 

facility works with the experimenter to supply replacement 

parts or to perform the repairs as soon as possible. 

Step 9: Data-Processing Support 

Although it is the PI’s responsibility to process the raw data 

into SEED format, PASSCAL offers extensive support. First, 

PASSCAL personnel train PIs on the use of programs used 

for data-quality support and data reduction. Data processed 

by the PIs are sent to the PASSCAL facility first for 

verification, are reviewed for completeness of waveforms 

and metadata, and are forwarded to the DMC for archiving. 

Step 10: End of the Experiment 

Coordination with PASSCAL at the end of an experiment 

is essential for a smooth transition to the next experiment. 

Final shipping documents are generated and PASSCAL 

personnel track the incoming equipment. Once the equipment 

is received from the field, it is scanned back into 

the inventory and routine testing and maintenance is conducted. 

PASSCAL personnel dedicated to data processing 

work with the experimenters to ensure that the final data 

are processed and archived. Any outstanding problems 

with the data are resolved at the PIC before being archived 

at the DMC. 

25

Telemetered Arrays 

Figure 20. Installation of a broadband sensor vault in southeastern 

Tibet with local assistance. 

to the permanent coverage provided by the GSN and other 

networks. Many global tomographers make increasing and 

extensive use of data from past PASSCAL deployments to 

enhance their data sets. At the request of this community, 

one station in each PASSCAL and EarthScope Flexible Array 

experiment is now designated as “open” with the typical twoyear 

data embargo waived. 

Maintaining and operating the broadband instrument pool 

consumes a significant portion of PASSCAL efforts. The 

broadband sensors were not designed for portable operations 

in the manner in which they are now employed; they 

are sensitive to shock and vibration during shipping. When 

being deployed in the field, care must be taken to ensure that 

the vaults do not flood or retain moisture. 

Using the same data-acquisition systems and sensors as in 

stand-alone deployments, telemetered arrays can be supported 

using specialized communications, software, and 

computing equipment. In addition to on-site recording to 

disk, data are telemetered to a central site and merged in 

real time (the on-site disks provide a backup for telemetry 

outages). The broadband telemetered array was developed 

in the early 1990s in collaboration with the University of 

California, San Diego, under the IRIS Joint Seismic Program 

(JSP) for deployment in the former Soviet Union for nuclear 

test-ban verification calibration tests. When the JSP program 

was completed, the equipment and expertise necessary to 

operate the array were transferred to PASSCAL. The original 

PASSCAL broadband array consisted of 32 broadband sensors 

and digitizers that telemetered the data via spread-spectrum 

radios to a concentrator site located up to 80 km away. 

This array was used for a number of experiments in locations 

as diverse as the South African craton, and the Wyoming 

province in the western United States. PASSCAL currently 

is supporting a 22-station telemetered array in southern 

Alaska. Telemetry expertise and new technologies developed 

and implemented in EarthScope are being incorporated 

into these systems. 

A large fraction of broadband experiments is conducted 

overseas in cooperation with foreign institutions. Foreign 

operations usually require significant effort in making 

arrangements for customs and shipping. While the PI is 

responsible for the costs associated with getting the instruments 

to the field, they usually rely on experienced PIC 

personnel to make these arrangements. 

Over PASSCAL’s lifetime, the average number of stations 

per deployment has steadily increased and is now 30, with 

many experiments exceeding 50, and several using more 

than 75. One ongoing NSF Continental Dynamics program 

experiment is fielding ~100 stations, 75 of which are from 

PASSCAL and 25 are university-owned. 

Figure 21. Radio telemetered broadband station on the Olympic 

Peninsula, above the Cascadia subduction zone. 

26

Controlled-Source Instruments 

provides support to UTEP at the level of approximately one 

FTE. EarthScope’s Flexible Array will also have 1700 TEXAN 

instruments upon completion of purchases. 

Active-source instruments can acquire large amounts of data 

in a short time period. To easily handle the data and make 

them easier to archive, PASSCAL is collaborating with the 

DMC to develop a new paradigm for archiving active-source 

data, based on the data format HDF-5. This new approach 

decouples the metadata (geographic and instrument data) 

from the seismic waveforms (similar to SEED), permitting 

more efficient archiving for PIs and PASSCAL. 

Figure 22. Single-channel TEXANs deployed in a dense array at Hill 

Air Force Base to image a toxic waste site. 

TEXANs 

Controlled-source experiments are designed to observe 

signals from man-made energy sources, such as explosions, 

airguns, and Vibroseis vibrators. The primary data 

requirements are for high-frequency recording (up to 500 

Hz) at high sample rates (100–1000 Hz) with precise timing. 

The REF TEK 125 “TEXAN,” designed and developed by a 

consortium of Texas universities and REF TEK, comprises 

the largest number of PASSCAL seismic channels used for 

controlled-source instruments. The single-channel TEXAN 

is small, lightweight (1 kg), runs on D-cell batteries, and 

especially easy to use. The typical experimental mode is 

to record specific timed segments, synchronized with the 

timing of artificial sources, although these instruments are 

also capable of recording for several days continuously. The 

instruments are often moved to occupy many sites—ease of 

deployment and recovery are principal design features. 

Multichannel Instruments 

PASSCAL maintains ten multichannel recording systems. 

These systems are commercial products developed for 

high-resolution seismic reflection and refraction experiments, 

including geotechnical applications and shallow 

petroleum exploration. The PASSCAL equipment consists 

of four Geometrics Stratavisor instruments that each record 

60 channels, and six Geometrics Geodes each of which 

record 24 channels. 

PASSCAL currently maintains ~ 550 TEXAN instruments 

and supports another ~ 440 through a cooperative agreement 

with the University of Texas, El Paso (UTEP). The UTEPowned 

systems are routinely used for PASSCAL experiments, 

effectively creating a combined pool for the user community. 

To maintain access to the UTEP instruments, PASSCAL 

Figure 23. Multichannel system recording mining 

blasts at the Tyrone Mine, New Mexico. 

27

PASSCAL owns two sets of cables for this system: one set 

is used for high-resolution shallow studies, and the second 

set, with longer stations spacing and lower-frequency geophones, 

is used in basin and crustal studies. PASSCAL also 

has Galperin mounts for high-resolution, three-component 

data acquisition. 

classrooms and field labs. One of the major uses for the 

multichannel equipment is in introductory geophysics 

courses such as the SAGE program (see http://www.sage.lanl. 

gov). The recorders along with associated processing software 

provide these courses with the ability to acquire, edit, and 

process reflection and refraction profiles. 

The multichannel equipment has been used very effectively 

for crustal imaging and a number of shallow studies of 

fault zones, aquifers, and hazardous waste sites, as well as 

extensively for training and education in undergraduate 

The number of experiments supported by this pool of instruments 

is now ~ 20 per year, with many experiments using 

multiple systems. 

RAMP: Rapid Array Mobilization Program 

PASSCAL reserves ten instruments for the RAMP instrument 

pool to enable very rapid response for aftershock recording 

following significant earthquakes. PASSCAL instruments 

were first used in an aftershock study at Loma Prieta, less 

than one month after the first instruments were delivered 

in 1989. The pool continues to be used both for aftershock 

studies and for special short-term projects that otherwise 

might not fit into the schedule. In the event of a significant 

earthquake requiring an aftershock response, RAMP instruments 

are available for shipping within 24 hours. 

The current RAMP pool now consists of 10 REF TEK RT130 

six-channel acquisition systems with 10 Trillium 40 (intermediate-period) 

sensors and 10 Kinemetrics ES-1 accelerometers. 

See Appendix G for RAMP deployment policy. 

Figure 24. Aftershock deployment after Landers 

earthquake in Southern California. 

28

Support 

The number of instruments available for use in experiments 

is frequently used to measure PASSCAL’s progress. However, 

the scope of the facility extends well beyond the hardware 

resource alone. The support the PIC provides to users is 

also essential to the overall success of a given experiment. 

PASSCAL support has evolved through time in response to 

experiment methodologies and technological advances, with 

a continuing emphasis on improving data return and finding 

more efficient methods of operation. Generally, the support 

provided can be divided into three categories (Figure 25): 

(1) pre-experiment, (2) experiment, and (3) post-experiment. 

Within these three categories efforts can be further 

usefully grouped into equipment support, shipping support, 

user training, experiment support, software support, and 

data processing support. 

Pre-Experiment Experiment Post-Experiment 

Logistics & Planning 

Pre-proposal 

Consultation 

Experiment 

Design Advice 

In-Field Support 

Huddle 

Training 

National & International 

Students & Collaborators 

Continued Data 

Archiving Support 

Conversion 

Software 

Gather 

Software 

pre-Archive 

Verification 

Documentation 

Software 

• Broadband deployment 

• Controlled Source 

Experiement 

Coordination 

Shipping & Customs 

Support 

Training 

Hardware 

Data QC 

Data QC 

Software 

metadata 

waveforms 

Experiment Specific 

Equipment 

Data Archiving 

state-of-healt 

Phone 

Shipping & Customs 

Support 

Troubleshooting 

email 

Equipment 

Maintanence 

Conversion 

Software 

Data 

Archiving Support 

Gather 

Software 

pre-Archive 

Verification 

Figure 25. PASSCAL Instrument Center Support Functions. There are three main phases of support from the PIC to the typical experiment: before, 

during and after the field deployment. 

29

Equipment Support 

With the exception of communications equipment, 

PASSCAL has traditionally developed instrument packages 

that use commercially supplied components from a variety 

of relatively small vendors. To maintain this fleet of highly 

specialized equipment, the PIC operates an extensive suite 

of instrument testing and repair procedures, particularly for 

the RT125s (TEXANs), RT130s, and Q330s, and broadband 

sensors and has developed an in-house inventory system that 

facilitates shipping and receiving equipment from the field, 

as well as tracks maintenance records (Figures 26 and 27). 

The PIC accepts instrument delivery from the manufacturer, 

performs acceptance tests, and maintains the equipment 

after receipt. In addition to initial equipment testing, the PIC 

provides general maintenance on all equipment. Personnel 

are trained to make board-level repairs as well as those that 

are identified by experience as “frequent.” Most major repairs 

are done by the manufacturers. In addition to repairing 

hardware, the PIC works with manufacturers to debug and 

test firmware bugs that are detected in the lab or field. 

The PIC coordinates shipping of instruments to and from 

locations all over the world in collaboration with the user 

community. Equipment is packed and shipped in special 

reusable shipping cases that are customized for various 

instrumentation components. All major items have barcode 

identification that is indexed to the inventory system and 

shipping records. 

Maintenance and Service 

Equipment supplied by PASSCAL commonly deployed under 

harsh field environments for periods sometimes exceeding 

two years. The PIC comprehensively tests and maintains 

instruments returned from the field to prepare them for 

further deployments. For a broadband station returning from 

the field, sensors are cleaned, function tested, then tested 

on a pier for several days. PASSCAL staff are responsible for 

reviewing and archiving sensor performance to ensure that 

they meet specifications. Generally, about 15% of sensors 

Sensor Sensor Flow Flow 

Datalogger 

Datalogger 

Flow 

Flow 

Receive Sensor Receive Sensor 

Receive Datalogger 

Receive Datalogger 

Inventory Sensor Inventory Sensor 

Inventory Datalogger 


Clean and Prep Clean and Prep 

Routine Maintenance 

Routine Maintenance 

Sensor 

Repair 

Sensor 

Repair 

Fail 

‘old’ sensor‘old’ sensor 

Sensor TestSensor Test 

Fail 

Test Analysis Test Analysis 

Fail Fail Pass Pass 

new sensornew sensor 

Inventory Sensor Inventory Sensor 

RMA RMA 

Datalogger 

Repair 

Function Test 

Function Test 

Datalogger 

Repair 

Fail 

‘old’ datalogger Fail 

Test Analysis 

‘old’ datalogger 

Test Analysis 

Fail 

Pass 

new datalogger 

Fail 

Pass 

new datalogger 


RMA Inventory Datalogger 

RMA 

Shipping 

Shipping 

Shipping 

Shipping 

Figure 26. Figure 27. 

30

FIELD QC1 

FIELD_QC2 

TRACKING 

Statistics 

& Reports 

INIT_PROJ 

WEB & DB 

GUI SEED 

Generation 

QC 

COMPLETENESS 

Ready for 

request 

Sending 

To PASSCAL 

ORB 

Report 

Sent 

DMC 

Summary 

Report 

ORB 

ftp & other 

alternative 

media 

ORB 

E-mail PI 

IN-HOUSE QC 

QC _1 

Completene s 

QC _2 

Data Format and 

consistency 

Working 

Area 

E-mail PI 

Sending 

to DMC 

Summary 

Report 

Report 

Sent 

INSTRUMENT CENTER 

40 

0 

-40 

-80 

Magnitude 

5.0 

9.5 

Earth 

Tides 

need additional attention during this turn-around evaluation. 

Sensors encountering problems are usually repaired in house 

by factory-trained staff (Figure 26 and 27). 

Three- or six-channel data acquisition systems, along 

with power systems and associated cables, are rigorously 

tested using routine procedures developed over the years. 

Specialized lab equipment and control software have been 

developed in house to streamline this testing process. 

Active-source and multichannel systems receive similar 

check-in and maintenance procedures after each use. The 

TEXAN active-source recorders additionally require routine 

adjustment of internal oscillators along with replacement 

and updates of batteries and firmware. 

All major repairs, testing, and maintenance procedures are 

logged into the equipment inventory database. Repair and 

other histories are readily accessible through this system, 

indexed by serial number. 

Shipping Support 

PASSCAL experiments are currently roughly split between 

domestic and international experiments. The PIC has two 

staff devoted to providing users with shipping support. These 

staff establish communications with carriers and provides 

users with quotes for various shipping options. They they 

typically arrange all carriers and provide shipping docu- 

mentation necessary for both domestic and international 

shipments. Once equipment leaves the PIC, PASSCAL 

tracks a shipments progress through customs clearance (in 

international cases) to delivery. At the end of an experiment 

PASSCAL provides assistance to PIs in arranging 

equipment return. 

User Training 

Instrument training for PIs, their students, postdocs, and 

staff is an essential component of PIC service. All PIs are 

required to visit the PIC for experiment-planning sessions 

and instrument training, as software and hardware upgrades 

often change best field practices for any particular instrument 

configuration. 

To reduce damage while the seismic equipment is deployed, 

PASSCAL personnel train users on instrument best use 

and care in the field. Training sessions include experiment 

planning meetings to ensure that the PASSCAL personnel 

understand experiment goals and can optimize how the 

equipment will be used during the experiment to meet these 

goals. Training materials, and hardware and software documentation, 

are provided during these sessions. 

PASSCAL also provides some liaison activities with international 

partners for joint experiments that use PASSCAL and 

other portable seismic instruments. 

T 

D 

IRIS 


PASSCAL 

Program for Array Seismic Studies of the Continental Lithosphere 

100 East Road 

New Mexico Tech 

Socorro, NM 87801 

(505) 835-5070 

www.passcal.nmt.edu 

Data Archiving Support 

ata collected with PASSCAL and/or USArray Flexible Array equipment are required to be archived 

at the IRIS Data Management Center (DMC) and are required to be openly available to the community. 

To facilitate data archiving, the IRIS PASSCAL data group provides PI support during data collection, 

quality assurance, and submission to 

the DMC. These efforts ensure that metadata 

and waveform data are synchronized 

prior to submission to the DMC archive. 

Specific to USArray Flexible Array 

experiments with on-site recording, the 

PASSCAL data group is responsible for 

the data archiving with the DMC. PASS- 

CAL utilizes software and documentation 

developed in house, at the DMC, 

and commercially for data collection and 

archiving on multiple computer platforms 

(Solaris, Linux, Windows, and Mac OS 

X). 

n addition to archiving support, the 

IRIS PASSCAL data group offers training 

sessions on data handling and quality 

control. They maintain close contact with 

PIs and data archivers before, during, and 

after experiments are deployed to seamless shepherd data from the field to the DMC in a timely process. 

The data group also works closely with the USArray Array Network Facility (ANF) when Flexible Array 

mixed on-site recording and telemetry experiments are fielded. 

new Quality Control System using commercial software that interfaces with Python, MySQL, and 

existing SEED tools is geared toward a more efficient path to perform quality control and submission 

of data to/from PASSCAL to the DMC. This new system will guide the user through the complete process 

in an organized, simple, and practical manner preventing common errors and difficulties. The new system 

incorporates a visual tracking interface to provide better monitoring, and quantitative and historic statistics 

of data passing through PASSCAL to the DMC. 

Phase 1 Phase 2 Phase 3 Phase 4&5 

Phase 8 

PIC SYSTEM 

Phase 9 

A 


U 

Phase 7 

PASSCAL 


D 


Phase 6 

The PASSCAL Dataloggers 

I 

T 

he PASSCAL software suite consists of programs written over the last two decades. The primary 

function of our software is to assist with collecting, performing quality control, and transforming 

data into formats usable for analysis and archiving with the IRIS DMC. The software is primarily to 

support dataloggers provided by the PASSCAL Instrument 

Center but has been used by many international institutions 

not associated with IRIS or PASSCAL. There are over 150 

fully open source programs ranging from simple command 

line programs, to graphical user interface programs, to fully 

graphical data viewing programs. The suite also contains 

many user contributed programs for performing tasks such 

as reading and writing mini-seed files and converting raw 

data to SEGY. 

unctionality of the PASSCAL software suite can be 

roughly broken into three categories: 1) Command and 

control of dataloggers both in-house and in 

the field. This includes bench testing utilities 

Minimal Set of Programs by Function 

that allow PASSCAL to quickly and efficiently 

test multiple dataloggers. 2) Format conversion 

Command & Format Quality 

routines that help the user manipulate the data 

Control Conversion Control 

into usable formats. 3) Quality control software 

geared toward field and archiving applications. changeo fixhdr logpeek 

PASSCAL provides pre-configured field computers 

containing the PASSCAL software suite as 

petm ref2mseed mseedpeek 

hocus neo mseedhdr 

well as commercial programs that may be needed 

pocus ref2segy pqlII 

for a particular experiment. 

setosc sdrsplit 1 rawmeet2 

ASSCAL software is freely available as both tscript tkeqcut refpacket 

pre-compiled binaries and source packages. 

tsp 

Binaries and packages for Mac OS X, Linux, and 

1 segyhdr 

Solaris can be downloaded from our anonymous 

txn2segy segyreelhdr 

ftp site (ftp://ftp.passcal.nmt.edu/passcal/software). 

segyVista 

trdpeek 

P 


he Incorporated Research Institutions for Seismology (IRIS) Program for Array Seismic Studies of 

the Continental Lithosphere (PASSCAL) Instrument Center and EarthScope USArray Array Operations 

Facility (AOF) at New Mexico Tech support cutting-edge seismological research into the Earth’s 

fundamental geological structure and processes. 

To support this research, PASSCAL maintains a 

pool of 24-bit Data Acquisition Systems (DAS), 

provides training on the installation and operation 

of the DAS, as well on site and remote technical 

support. 

sed with a variety of sensors for both active 

source and passive source experiments, the 

three-channel DAS is the most versatile in our 

pool. These DAS synchronize their internal oscillators 

to an on-site GPS receiver. They can store 

as much as 20 Gbytes locally or telemeter data 

to a central site via Ethernet or serial ports. The 

three-channel DAS can record sample rates ranging 

from 1 to 1000 samples per second (sps) continuously 

or in programmed recording windows. 

esigned as small, light weight, and easily deployed instruments, the single-channel DAS are primarily 

used for active source reflection and refraction surveys. Once deployed, the units can run for 7 to 

10 days on a single pair of “D” cell batteries. Data are stored in internal flash ram, ranging in size from 

32 Mbytes to 256 Mbytes, at sample rates up to 1000 sps. An internal oscillator is synchronized to GPS 

time before and after deployment. 

he multi-channel units are capable of 

recording up to 50,000 sps. The multichannel 

recorders can be connected together 

PASSCAL Flexible Array 

250 to provide more channels than a single unit 

1200 alone. These recorders are cable systems normally 

used with single component geophones 

x 60 for refraction or reflection surveys. 

x 24 6 

Sensor Type Channel 850 1000 4 

Three Single Channel Multi-Channel Multi-Channel DAS Inventory 

100 East Road 



(505) 835-5070 


P 

T 


PASSCAL 


PASSCAL Software Suite 

F 


PASSCAL 


1-contributed programs 

2-not yet released 

100 East Road 



(505) 835-5070 


100 East Road 



(505) 835-5070 


he IRIS PASSCAL Instrument Center maintains sensor pools for both PASSCAL and USArray 

Flexible Array experiments. The equipment is loaned to research scientists to investigate Earth’s 

structure, deformation, and history. PASSCAL experiments typically target questions of Earth structure 

and history ranging from the uppermost crust 

down to the deep interior, using both artificial 

T 

and natural sources of seismic energy. Data 

from PASSCAL experiments also illuminate 

short-term deformation processes: earthquakes, 

volcanic eruptions, and tremor episodes. Recently, 

questions about Earth’s climate and glacial 

processes are being investigated. Flexible 

Array instruments are being used to increase 

resolution of key areas within the larger USArray 

Transportable Array. 

ensors available for loan to principal investigators 

range from broadband three-component 

seismometers to high-frequency, singlecomponent 

geophones. Broadband deployments 

typically record continuously for several years, 

most often as arrays of stand-alone stations. 

Earthquakes and other seismic sources recorded 

during the experiments provide data 

S 

PASSCAL Polar Support 

http://www.passcal.nmt.edu/Polar 

Sensor Inventory 

Flexible Array 

121 

100 

190 100 

High-Frequency 420 

Single Component High-Frequency 

Type Broadband Mid-Band Short-Period PASSCAL 450 3000 1610 

100 East Road 



(575) 835-5070 


ASSCAL currently supports approximately 60 experiments per year worldwide, with 5-10% currently 

funded by the National Science Foundation (NSF) Office of Polar Programs (OPP). Polar projects 

commonly require a level of support that is several times that of seismic experiments in less demanding 

environments inclusive of very remote deployments (e.g. Tibet). In order to ensure OPP funded Antarctic 

projects the highest level of success, we have established 

a PASSCAL Polar Program and have secured 

funds from OPP to support new and ongoing experiments 

in Antarctica. 

he primary focus of PASSCAL’s Polar support 

efforts are: 1) Developing successful cold station 

deployment strategies. 2) Collaborating with vendors 

to develop and test -55°C rated seismic equipment. 3) 

Establishing a pool of instruments for use in cold environments. 

4) Building a pool of cold station ancillary 

equipment. And 5) Creating a resource repository for 

cold station techniques and test data for seismologists 

and others in the polar sciences community. 

ur strategy for designing cold-hardened seismic 

systems is driven by the need to maximize heat 

efficiency and minimize payload while maintaining continuous recording throughout the Polar winter. 

Power is provided by a primary Lithium Thionyl Chloride battery pack and is backed by a secondary, solar 

charged AGM battery pack. Station enclosures are heavily insulated utilizing vacuum-sealed R-50 component 

panels and rely on instrument-generated heat to keep the dataloggers 

within operating specification. Although insulated, broadband sensors are 

operated close to ambient temperature. 

n parallel with PASSCAL’s internal Polar support efforts, IRIS and 

UNAVCO in 2006 received NSF MRI funding to develop a power and 

communications system for remote autonomous GPS and seismic stations 

in Antarctica. In 2007, IRIS was awarded a second NSF MRI to begin 

establishing a pool of seismic instrumentation and station infrastructure 

packages designed to operate PASSCAL experiments in Polar Regions. 

I 


PASSCAL 



The PASSCAL Sensors 

-120 

-160 

-200 

-240 

0.001 0.01 

Equivalent Earth Peak Acceleration (20 log m/sec 2 ) 

Short Period 

Mid-Band 

Active Source 

Regional 

Low Earth Noise 

Magnitude 

0.1 1 10 100 1,000 10,000 100,000 

Period (Seconds) 

for mapping Earth structure on a variety of 

scales, as well as investigating regional and 

global tectonics. Active-source experiments 

use a large number of closely-spaced stations 

programmed to record artificial energy 

sources at high sample rates over the course 

of days or weeks. The high-frequency 

sources and close station spacing of these 

experiments can resolve fine structure of 

the crust and upper mantle and yield clues 

to their long-term history. 

Figure 28. The suite of PASSCAL one-pager documents used for 

general outreach. 

T 

O 

T 

Flexible Array Inventory 

3 Channel DAS 250 


Broadband Sensor 121 

Short Period Sensor 100 

Broadband 

Teleseismic 

STS-1 

A celerometer 

he Incorporated Research Institutions for Seismology (IRIS) Program for Array Seismic Studies 

of the Continental Lithosphere (PASSCAL) Instrument Center and EarthScope USArray Array 

Operations Facility (AOF) at New Mexico Tech support cutting-edge seismological research into Earth’s 

fundamental geological structure and processes. The 

facility provides instrumentation for National Science 

Foundation, Department of Energy, and otherwise 

funded seismological experiments around the world. 

PASSCAL experiment support includes seismic instrumentation, 

equipment maintenance, software, data 

archiving, training, logistics, and field installation. 

ontinued expansion of IRIS activities at New 

Mexico Tech via the EarthScope and other 

initiatives has spurred a major facility expansion, the EarthScope USArray Array Operations Facility. 

The AOF was officially dedicated on April 6 2005 by the 

New Mexico Tech administration and the IRIS Board of 

Directors. The combined PASSCAL Instrument Center 

and AOF currently support a total of 32 professional New 

Mexico Tech and IRIS staff, as well as a contingent of 3 Channel DAS 850 

student workers. 


Multichannel 4 x 60 Channel 

ASSCAL and USArray Flexible Array equipment is 

available to any research or educational institution to 

6 x 24 Channel 

use for research purposes within the guidelines of established 

policies. These policies provide that data collected Short Period Sensor 270 

Broadband Sensors 450 

with PASSCAL and/or USArray equipment be archived at High Frequency 400 

Sensors 

P 


PASSCAL 

The PASSCAL Facility 

C 



Dynamic Range 

100 East Road 



(505) 835-5070 


PASSCAL Inventory 

the IRIS Data Management Center and that the 

data are openly available to the community. 

Policies, guidelines and Instrument Request 

Forms can be found on the PASSCAL web 

site. 

31

Experiment Support 

For any type of experiment, PASSCAL personnel assist PIs 

throughout the project to solve technical problems, including 

repairing instruments on site, troubleshooting problems 

remotely via telephone, and arranging shipments of replacement 

equipment (see Appendix F). 

In passive-source experiments, PASSCAL personnel arrive 

shortly after the equipment arrives in the field. They are 

responsible for testing and repairing any equipment that 

may have been damaged during shipping, and providing 

in situ training for field personnel. PASSCAL staff usually 

participate in some initial station deployments to provide 

additional PI training. Once this initial support is finished, 

the PIC will continue to support the PI during the experiment, 

either on site or remotely, as necessary. 

PASSCAL staff normally accompany active-source groups 

for their entire duration to ensure time-critical instrument 

deployments, to make repairs on instruments in the field, 

and to assist in the download of data and organization of 

metadata. 

Software Support 

The PASSCAL software suite comprises programs written 

over the last two decades by PASSCAL staff and the wider 

community. The primary function of PASSCAL software 

is to assist with collecting, performing quality control, and 

transforming data into optimal formats for analysis and 

archiving with the IRIS DMC. The software is primarily 

designed to support dataloggers provided by the PIC but has 

been used by many international institutions not associated 

with IRIS or PASSCAL. There are over 150 fully open-source 

programs ranging from simple command line programs, to 

graphical user interface scripts, to fully graphical data viewing 

programs. The suite also contains many user-contributed 

programs for performing tasks such as reading and writing 

miniSEED files and converting raw data to SEGY format. 

In-house 

Inventory/Maintenance 

Database 

Lab Tools 

Data Flow 

Purchasing 

Forms 

Software Development 

Team 

Waveform QC 

State-of-Health 

Analysis 

Archive Formatting 

of data & metadata 

Datalogger 

Interfacing 

User Community 

Data Transfer 

Tools 

Field-Specific QC 

Tools 

Datalogger Offload 

Tools 

Figure 29: PASSCAL software development serves both PASSCAL staff and the user community. 

Development both in-house and user-community software is a dynamic process 

reliant on user feedback. 

Functionality of the PASSCAL software suite 

can be roughly broken into two partially 

overlapping categories (Figure 29): in-house 

and user-community software. In-house 

software includes bench-testing utilities 

that allow PASSCAL staff to quickly and 

efficiently test multiple dataloggers and to 

update associated inventory and maintenance 

database. User-community software includes 

quality control code geared toward field and 

archiving applications. Examples of widely 

used software with overlapping in-house 

and user-community uses include waveform 

viewing tools, state-of-health analysis tools, 

and format conversion routines. PASSCAL 

provides pre-configured field computers containing 

the PASSCAL software suite as well as 

commercial programs that may be needed for 

a particular experiment. 

32

Data Processing Support 

Prior to, during , and following an experiment, PASSCAL 

personnel work with the PI and staff responsible for 

archiving the data on the use of essential quality-control and 

processing tools (Figure 30). During passive experiments, 

PASSCAL personnel receive and verify preliminary SEED 

data, working closely with both the PI and DMC personnel 

to assure data and metadata completeness, accuracy, and 

quality. Verified SEED data sets from passive experiments 

are forwarded to the DMC for archiving as soon as possible, 

usually during the experiment. 

Active-source data are normally collated and verified following 

the experiment. A new archival data format, HDF-5, has 

recently been adopted so that active-source metadata can be 

corrected without having to re-archive the whole data set at 

the DMC. Software for archiving and retrieval is currently 

being tested. This software will provide the active-source 

experimentalists with a data-retrieval model similar to that 

for the passive experimentalists—the DMC acquires the data 

at an early stage, and maintains the waveform and metadata 

independently (see Appendix C). 

PASSCAL Experiment 

raw data 

metadata 

PI 

Archive 

ready 

SEED or 

SEGY 

ftp 

orb 

media 

PASSCAL/AOF 

Accept SEED data 

Delivery Verification 

Check SEED Veracity 

Archive 

ready 

SEED or 

SEGY 

Flexible Array Experiment 

PI 

raw data 

metadata 

ftp media orb 

raw data 

metadata 

Create datasync and 

update Sent db 

Bundle & 

Ship to DMC 

Archive 

ready 

SEED or 

SEGY 

ftp 

orb 

DMC 

bob 

Verify Delivery 

and Data Archiving 

Figure 30. Flow of data from the PI to the IRIS Data Management Center. 

33

Interactions Between the IRIS Data Management 

System and PASSCAL Programs 

Twenty years ago, few people anticipated the present scope 

of PASSCAL’s data-generation capabilities. Instead of being 

dominated by active-source data sets in SEGY format, the 

PASSCAL facility has evolved into one largely dominated 

by broadband data collected during dozens of multiyear 

experiments led by numerous PIs. Proper archival of data 

and metadata for the long-term benefit of the community is 

obligatory for essentially all science-driven uses of PASSCAL 

instrumentation, and requires substantial interaction 

between PASSCAL and the IRIS Data Management System. 

Data Availability 

Permanent archival of broadband data from PASSCAL 

experiments is now routine and relies heavily upon close 

coordination between the PIC and the IRIS DMC in 

Seattle. SEGY data sets from active-source experiments also 

continue to routinely flow to the DMC (Figure 31). PIC personnel 

performs all front-line quality control on PASSCAL 

data and metadata. 

At the end of 2007, the IRIS DMC had 2.22 terabytes of 

assembled PASSCAL data archived and 14.97 terabytes of 

broadband data available in SEED format.Total PASSCAL 

Archive Size (terabytes) 

80.0 

70.0 

60.0 

50.0 

40.0 

30.0 

20.0 

10.0 

0.0 

Jan-92 

Jan-93 

Jan-94 

Jan-95 

Jan-96 

IRIS DMC Archive Growth 

Single Sort 

January 1, 2008 

Jan-97 

Jan-98 

Jan-99 

Figure 31. PASSCAL data form one of the largest data volumes at the 

IRIS DMC, second only to US regional networks. 

Jan-00 

Date 

Jan-01 

Jan-02 

Jan-03 

EarthScope 

PASSCAL 

Engineering 

US Regional 

Other 

JSP 

FDSN 

GSN 

Jan-04 

Jan-05 

Jan-06 

Jan-07 

Jan-08 

DMC holdings are now approximately 25% of the DMS 

archive—roughly 30% more data than the IRIS GSN archive, 

and include data from 3,862 PASSCAL stations in its archives. 

A key feature at the DMC is that its various request tools 

can generate requests for SEED-formatted data volumes 

for users regardless of whether those data were collected by 

the GSN, FDSN partners, US regional networks, USArray, 

or PASSCAL. For instance, a simple query procedure using 

the jWEED program allows a user to draw a region on a 

world map and request all broadband data collected within 

that box. This was not originally anticipated as a capability 

when IRIS was originally formed, but now allows for the 

seamless use of the worldwide broadband data resource by 

the broad community. 

PASSCAL Data Distribution 

GSN data are the most frequently requested single data 

source at the DMC, but the amount of distributed PASSCAL 

data is also very large (Figure 32). The annual request rate 

is also accelerating for both data sets with a doubling time 

of approximately two years. Data volume requested from 

PASSCAL sources is currently more than one-half of that 

requested from GSN sources (e.g., 9.9 terabytes total as 

compared with 18.4 terabytes for the GSN). Although the 

Transportable Array is in many respects the most exciting 

new data source in seismology, total shipments from 

PASSCAL experiments currently still exceed data shipments 

for the Transportable Array (9.9 terabytes as compared to 7.4 

terabytes) and only last year did more data ship on an annual 

basis from the Transportable Array than from PASSCAL (3.8 

terabytes from the Transportable Array as compared with 3.4 

terabytes for PASSCAL). 

Support for Assembled Data from Controlled 

Source Seismic Experiments 

The PASSCAL Instrument Center continues to improve 

support for SEGY format data. Over the past two years, 

PASSCAL and the DMS have developed a system based 

34

Shipments By Program 

(all methods) 

through December 31, 2007 

gigabytes shipped 

30,000.00 

25,000.00 

20,000.00 

15,000.00 

10,000.00 

2007 

2006 

2005 

2004 

2003 

2002 

5,000.00 

0.00 

GSN PASSCAL DMS (Other) USArray 

(TA,BK,CI) 

Figure 32. Data volume distributed by the DMC for GSN, 

PASSCAL, other DMC sources, and for the major components 

of the EarthScope Transportable Array. These statistics have 

been compiled since 2002 and are updated monthly by the 

DMC. 

upon the HDF-5 format that allows better management of 

and access to SEGY data, the standard archive format for 

controlled-source data. PASSCAL electronically transfers 

HDF-5 files to a specific directory on a DMC machine. 

Scripts at the DMC produce Web forms that allow users to 

view details about shot points and sensor locations from 

which they can determine what data can be requested. 

The motivation to develop this PASSCAL-DMS Web form 

was to simplify data curation, specifically in the area of 

separating metadata from waveform data. This structure 

reduces the data-processing burden on PIs as they uncover 

errors in the metadata; they no longer have to rewrite an 

entire data set, but instead simply correct the metadata. This 

development has also produced a new request tool where the 

IRIS DMC is better able to service the community’s requests 

for this type of data. 

The new system to support SEGY data was developed by 

PASSCAL staff and allowed DMC staff to focus on the development 

of the Web components of the system. Although 

this new system has not yet been officially released, it is well 

developed and will improve distribution and support for 

SEGY data sets to the broad community. 

35

Box 2: A Guide to the PASSCAL Instrumentation Center Web Site 


Information provided on the PASSCAL Web site is targeted 

at the user community. Although every project has unique 

features, basic policy and contact information needed by 

the user community to initiate support is present there. PIs 

can use the Web site to interact with PIC staff for instrument 

and scheduling requests, and during experiment and 

logistics planning, training, data collection, and data archival. 

During proposal writing or experiment planning, the 

PIC Web site provides general technical information about 

supported instrumentation and online access to PASSCAL 

support schedules, which can be especially important 

when contemplating large, broadband experiments. While 

an experiment is active, users frequently access the Web 

site for detailed procedures or technical specifications, to 

access PASSCAL software, and for data archiving information. 

The Web site also services requests for software or 

instrumentation specifications for researchers or students 

using archived data from the IRIS DMC. The PIC Web site 

was designed and developed prior to the advent of content 

management systems (CMS), which are now standard for 

maintaining and creating large Web sites. Thus, PASSCAL 

initiated a site redesign in January 2008 with professional 

consultation. This redesign will implement CMS and 

organize the site based on common-use profiles. The new 

site is scheduled to be operational in late 2008. The current 

structure and content of the Web site is outlined below. 

SUPPORT 

Equipment 

available Equipment (http://www.passcal.nmt.edu/user_support/equipment_inventory.html) 

inventory (http://www.passcal.nmt.edu/user_support/inventory_chart.html) 

Software (http://www.passcal.nmt.edu/software/software.html) 

Shipping 

estimate shipping (http://www.passcal.nmt.edu/user_support/shipping.html) 

list of shippers (http://www.passcal.nmt.edu/user_support/shippers.html) 

Training 

Scheduling and planning (http://www.passcal.nmt.edu/user_support/Training/preparing.html) 

agenda (http://www.passcal.nmt.edu/user_support/Training/planning.html) 

feedback form (http://www.passcal.nmt.edu/user_support/Training/feedback.html) 

Visiting PASSCAL 

directions and maps (http://www.passcal.nmt.edu/user_support/map2PASSCAL.html) 

lodging (http://www.passcal.nmt.edu/user_support/lodging.html) 

Virtual tour (http://www.passcal.nmt.edu/user_support/tour_1.html) 

Contact Information 

general contact (http://www.passcal.nmt.edu/user_support/contact.html) 

Staff directory (http://www.passcal.nmt.edu/user_support/staff.html) 

How Tos 

racS (Redundant Array Copy System) (http://www.passcal.nmt.edu/user_support/Training/racs.html) 

ref TEK timing correction file (http://www.passcal.nmt.edu/user_support/Training/PCF_tutorial.doc.pdf) 

calibrating and Autosensorting (http://www.passcal.nmt.edu/user_support/Training/Calibration.html) 

emergency laptop install of RH 7.0 (http://www.passcal.nmt.edu/user_support/Training/RHInstall.html) 

FAQs (http://www.passcal.nmt.edu/user_support/faqs.html) 

SCHEDULES 

Broadband 

2007–2008 (http://www.passcal.nmt.edu/schedules/BB07-08.html) 



Intermediate period 2007–2008 (http://www.passcal.nmt.edu/schedules/IP07-08.html) 

Short period 2007–2008 (http://www.passcal.nmt.edu/schedules/SP07-08.html) 

TEXAN 2007–2008 (http://www.passcal.nmt.edu/schedules/TXN07-08.html) 

36

FORMS 

Instrument request forms PASSCAL and USArray (http://www.passcal.nmt.edu/forms/request.html) 

PASSCAL rebill (http://www.passcal.nmt.edu/forms/PASSCAL_Rebill_Form.html) 

Request FDSN network code (http://www.iris.edu/scripts/getcode.html) 

Mobilization form (http://www.iris.edu/stations/mob.htm) 

Demobilization form (http://www.iris.edu/stations/demob.htm) 

Evaluation forms (http://www.passcal.nmt.edu/forms/EvalForms.html) 

INSTRUMENTATION 

Sensors 

comparison chart (http://www.passcal.nmt.edu/instrumentation/Sensor/sensor_comp_chart.html) 

Specification sheets (http://www.passcal.nmt.edu/instrumentation/Sensor/sensor_info.html) 

Data Acquisition Systems 

geode (http://www.geometrics.com/seismographs/Geode/geode.html) 

geometrics RX60 (http://www.geometrics.com/nxdesc.html) 

Quanterra Q330 (http://www.q330.com/) 

ref TEK R125 (http://www.reftek.com/products/125-01.html) 

ref TEK RT130 (http://www.reftek.com/products/130-01.html) 

Information and Policy 

Instrument use policy (http://www.passcal.nmt.edu/information/Policies/InstUse_Policy.htm) 

Instrument use agreement (http://www.passcal.nmt.edu/information/Policies/InstUse_Agreement.htm) 

Field staffing policy (http://www.passcal.nmt.edu/information/Policies/PASSCAL_Field_Policy.htm) 

Data delivery policy (http://www.passcal.nmt.edu/information/Policies/data.delivery.html) 

RAMP policy (http://www.passcal.nmt.edu/information/Policies/RAMP_policy.html) 

Standing committee (http://www.iris.washington.edu/about/committees.htm#passcal) 

Instrumentation report (http://www.passcal.nmt.edu/information/inst_rpt_2001.html) 

USArray 

Flexible Array information for the PI (http://www.passcal.nmt.edu/information/Flexible_Array.html) 

Instrument request form (http://www.passcal.nmt.edu/forms/requestUS.fillout.html) 

Flexible Array data policy (http://www.passcal.nmt.edu/information/Policies/FA_DataPolicy.html) 

Data archiving responsibilities (http://www.passcal.nmt.edu/information/Policies/FA_archiving.pdf) 

Schedules (http://www.passcal.nmt.edu/schedules_FA/Index.html) 

EarthScope home page (http://www.earthscope.org/) 

EarthScope data management plan (http://www.iris.iris.edu/USArray/files/USDataPlan_FinalV7.pdf) 

USArray design workshop (http://www.passcal.nmt.edu/information/arraydesign.html) 

Experiment Profiles 

1986–1995 (http://www.passcal.nmt.edu/schedules/experiment_profiles/exp8695.html) 

1996–1999 (http://www.passcal.nmt.edu/schedules/experiment_profiles/exp9699.html) 

2000 (http://www.passcal.nmt.edu/schedules/experiment_profiles/exp2000.html) 







Polar Support (http://www.passcal.nmt.edu/Polar/index.html) 

37

Cooperation with Other 

Facilities and Agencies 

NSF funds IRIS to support facilities for a broad range of 

seismological studies. All IRIS data are openly available to 

all interested researchers and to the public, and requests for 

use of PASSCAL instrumentation will be accepted from any 

qualified research organization. NSF- or DOE-funded proj- 

ects receive first priority. Other requests are filled based on a 

priority ranking, as defined in the PASSCAL Instrument Use 

Policy (Appendix B), and on an as-available basis to other 

US federal projects and foreign institutions. 

UNAVCO 

Collaborative efforts with the geodetic consortium, 

UNAVCO, have been strengthened recently through 

EarthScope and NSF Office of Polar Programs (OPP) 

activities. The USArray Array Operations Facility hosts 

computers used by the GAMIT-based Analysis Center of the 

EarthScope Plate Boundary Observatory (PBO) in association 

with PI Mark Murray (NMT). The PIC also hosts a PBO 

Strainmeter Analysis Center for two full-time UNAVCO 

staff and provides a server room to accommodate a backup 

data management facility for PBO. 

Figure 33. UNAVCO collaboration. 

PASSCAL and GSN collaborations with UNAVCO driven by 

new opportunities in polar science have fostered successful 

pursuit of a joint Antarctic facility project under NSF Major 

Research Instrumentation (MRI) grant for instrument development 

(“A Power and Communication System for Remote 

Autonomous GPS”). This effort was first funded in 2006 and 

has recently resulted in the deployment of second-year field 

prototypes of geodetic and seismological instrumentation in 

the deep Antarctic interior for two NSF-funded OPP efforts: 

POLENET and AGAP. This Antarctic MRI effort is advised 

by a Polar Networks Science Committee, currently chaired 

by Terry Wilson (Ohio State University). 

Network for Earthquake Engineering Simulation (NEES) 

NEES is a national earthquake engineering resource funded 

by the NSF Engineering Directorate that includes geographically 

distributed, shared-use experimental research equipment 

sites built and operated to advance research in earth- 

quake engineering. One of the NEES equipment sites with 

particular relevance to PASSCAL is located at the University 

of Texas at Austin. This facility is home to three truckmounted 

vibrators purchased to study near-surface soil 

38

properties and investigate soil-structure interactions. These 

vibrators also have been used in collaborative geophysical 

investigations as sources for studies of deep basin structure. 

Over the last few years, several experiments have been conducted 

combining the NEES vibrators and sensors from the 

PASSCAL pool. In these experiments the PIs make the initial 

arrangements for the experiment while PASSCAL and NEES 

staff coordinate scheduling and technical arrangements. 

Figure 34. NEES vibrator deployed with PASSCAL multichannel 

systems in Garner Valley, California (Photo c/o Jamie Steidl, UCSB) 

Ocean Bottom Seismograph Instrument Pool (OBSIP) 

OBSIP is analogous to PASSCAL in that it is a multi-user 

pool of seismological instruments made available to the 

research community. In the case of OBSIP, instruments are 

funded through the NSF Division of Ocean Sciences and are 

designed to operate autonomously on the ocean floor. Some 

OBSIP experiments are carried out in remote ocean basins 

and rely solely on ocean bottom instruments. Experiments 

involving interactions with PASSCAL, include active-source, 

onshore-offshore experiments (often coupled with air guns 

and hydrophone streamers), and long-term deployments for 

earthquake and structure studies at continental margins and 

oceanic islands. 

Because of complex logistics and the high cost of ship time, 

the PASSCAL and OBSIP groups work closely together to 

schedule joint experiments. One of the OBSIP PIs (John 

Collins) was recently a member of the PASSCAL Standing 

Committee. Although no longer a voting member, Dr. Collins 

continues to attend meetings and otherwise advise PASSCAL. 

The PASSCAL Program Manager is a member of the OBSIP 

Oversight Committee and regularly communicates with 

OBSIP operations. The PASSCAL Instrument Request Form 

flags experiments proposing use of equipment from both the 

PASSCAL and OBSIP facility. This additional alert ensures 

that schedulers become aware of the need to coordinate at 

the earliest opportunity. In addition to interactions with IRIS 

related to PASSCAL instrumentation, OBSIP facilities also 

arrange for all OBSIP data to be archived at the IRIS DMC. 

University-National Oceanographic 

Laboratory System (UNOLS) 

UNOLS is responsible for coordinating activities of the 

academic research fleet used in most NSF experiments in 

ocean sciences. UNOLS also sets schedules for vessels used 

in marine geophysical studies, including those involving 

PASSCAL instruments. Staff from OBSIP and PASSCAL staff 

attend scheduling meetings for the UNOLS ships and work 

to identify and resolve potential problems associated with 

coordinating instrument and ship schedules. 

39

US Geological Survey 

There is close collaboration between IRIS and the USGS 

throughout all IRIS programs. PASSCAL instruments 

are used in USGS-sponsored experiments (frequently 

with participation of university PIs) and USGS investigators 

frequently are collaborators on NSF-funded 

experiments. USGS participation is especially com- 

mon in earthquake hazard studies as part of the USGS 

National Earthquake Hazards Reduction Program 

(NEHRP), and in active-source studies in which the 

USGS brings valuable capabilities in explosive handling 

and permitting that university partners commonly lack. 

Departments of Energy and Defense 

US programs in seismic verification of nuclear test ban treaties 

and nuclear nonproliferation are primarily supported 

by DOE and DOD. These programs also support the US 

mission to monitor nuclear explosions in real time, support 

research efforts in the identification and characterization 

of explosion sources, and the characterization of regional 

seismic wave propagation. Efforts conducted by academic, 

private, and government investigators, make use of openly 

available, archived data from IRIS—including PASSCAL 

and GSN. In many cases, PASSCAL data, often collected for 

other scientific reasons, provide unique regional data that are 

key to characterizing natural and anthropogenic seismicity 

and wave propagation. Field experiments directly supported 

by DOE’s National Nuclear Security Administration and the 

Air Force Research Laboratory have used instrumentation 

from the PASSCAL facility. In 2001–2004, DOE provided 

funding, through interagency transfer to NSF, to support 

the upgrading of a significant portion of the PASSCAL 

broadband instrument pool. In recognition of this support, 

the PASSCAL Instruments Use Policy (Appendix B) was 

modified to provide DOE-funded experiments equal priority 

in scheduling with NSF experiments. 

Foreign Institutions and International Partnerships 

A number of international groups have acquired portable 

instruments that are similar (and in many cases identical), 

to those of PASSCAL. Centrally managed facilities operating 

and maintaining seismic sensors exist in Canada and many 

European and Asian countries, and large-scale projects 

modeled after US initiatives, such as EuroArray, have 

started to develop. 

International, multi-institutional experiments have been 

organized to take advantage of merged instrument pools, 

permitting experiments to draw on a larger instrument base 

than is typically realizable with instruments from only one 

facility. These collaborative opportunities include both use of 

PASSCAL equipment overseas and use of foreign equipment 

in the United States. 

This is especially true in the case of large-scale, active-source 

crustal investigations incorporating TEXAN-style instruments. 

Although PASSCAL does not officially exchange 

instruments with other facilities, the PASSCAL staff work 

with PIs and their foreign collaborators to coordinate instrument 

schedules so that, if at all possible, PASSCAL instruments 

can be in the field at the same time as instruments 

from international pools. During the last five years, joint 

international experiments of this type have been conducted 

in Poland, Denmark, Jordan, Israel, Tibet, Venezuela, Costa 

Rica, New Zealand, Ethiopia, and Italy. For longer-term 

broadband deployments, US investigators sometimes 

develop collaborative, but separately funded, experiments 

with foreign teams to achieve expanded coverage in 

complementary studies. This future mode of collaboration 

has significant potential, for example, in Europe and China, 

40

where a moderately large national, PASSCAL-like facilities, 

are being developed, and in Antarctica, with its many international 

research participants and bases. 

groups of regional scientists, assistance with hardware or 

software development, or in minor repairs and upgrades of 

PASSCAL-compatible instrumentation. 

In addition to working with the international community to 

coordinate instrument deployments, IRIS also works with the 

international Federation of Digital Seismographic Networks 

(FDSN) to make data from foreign-coordinated experiments 

with portable instruments openly available after a short 

waiting period in a manner that is analogous to the PASSCAL 

data policy. The “open” data policy and culture encouraged 

by IRIS has already had significant impact on the routine 

sharing data from permanent global networks and US-lead 

portable experiments. The extension of this culture to include 

data from all portable deployments worldwide would be a 

significant advance international earth science. 

PASSCAL’s primary function has been to support NSFfunded 

experiments. However, opportunities exist at little 

cost to expand the purview of this resource to benefit seismology 

more broadly through the world. Through numerous 

field programs, PASSCAL investigators have developed 

a web of international scientific contacts throughout most of 

the scientifically interesting regions of the planet. In many 

cases, PASSCAL field personnel have provided technical 

advice and assistance to scientists in developing countries 

on an ad hoc basis, appropriate to the particular experiment 

being supported. In a small number of carefully selected 

cases, this relationship has been extended on a more formal 

basis through long-term loans of depreciated equipment and 

by serving as a pool of expertise to frequent foreign scientists 

who are also operators of in-country seismic equipment. In 

2006, IRIS instituted a long-term loan program with foreign 

partners to utilize the retired PASSCAL REF TEK 72a 

series recorders. This program is coordinated through a 

proposal and selection process overseen by a panel that 

includes representation from IRIS Planning, PASSCAL, 

and DMS staff. A flagship pilot project for this effort has 

been working with AfricaArray, an NSF Partnerships for 

International Research and Education (PIRE) program that 

is seeding new long-term seismographic stations and student 

opportunities throughout the continent. Future initiatives 

could take the form of technical training sessions at PIC for 

Developing World 

• PASSCAL is a principal global technical resource for 

seismology. 

• Many of the established contacts in Africa, central Asia, 

and South America can be formalized to provide technical 

guidance on equipment purchase, installation, and 

maintenance. 

• In some cases, PASSCAL can act as an equipment 

resource for long-term loan of depreciated instruments. 

This model has been successfully used to develop 

AfricaArray and is being pursued in the IRIS Long-term 

Loan Program. 

Developed World 

• IRIS and PASSCAL can establish collaborative agreements, 

including joint use of instrumentation, with other 

centers for portable seismology. 

• PASSCAL can use its successes and user community to 

advocate that the open data model be adopted for all 

portable experiments and central data centers. 

41

Management and 

Oversight 

The PASSCAL Instrument Center operates under annually 

revised subawards from IRIS to New Mexico Tech. The PIC 

presently has a total PASSCAL and USArray staff of 31 (with 

two pending), including a Director, software and hardware 

staff, office managers, and office personnel (Figure 35). 

The PIC supports PASSCAL core operations as well as 

significant EarthScope Flexible and Transportable Array 

operations. EarthScope support is provided by the Array 

Operations Facility (AOF), which is responsible for most 

purchasing, delivery, checkout, and final integration and 

Marcos Alvarez 

Deputy Program Manager 


Jim Fowler 

Program Manager 

IRIS PASSCAL 

Standing Committee 

Alan Levander, Rice Univ. 

Chair 

Figure 35. Organizational chart for 

the IRIS PASSCAL Instrument Center 

as of February 2008. 

NMT 

Rick Aster 

Faculty 

Principal Investigator 

PASSCAL 

EarthScope Array Operations Facility 

Earthscope TA Coordinating Office 

Distributed 

Bruce Beaudoin 

Director 

Mike Fort 

Associate Director 

Hardware Manager 

Noel Barstow 

Logistics/Sensor Manager 

Steve Azevedo 

Software Manager 

Bob Busby 

TA Manager 

Patricia Griego 

Office Manager 

Jackie Gonzales 

Shipping 

Michael Gorton 

Inventory Control 

Pina Miller 

Logistics 

Bob Greschke 

Software 

Steve Welch 

TACO Manager 

Cheryl Etsitty 

Coord. Office Tech 

Elena Prusin 

Accounting 

Cathy Pfeifer 

TA Manager 

Pete Ulbricht 

Sensor Repair 

Kanglin Xu 

Software 

Sandra Azevedo 

Site Coordinator 

Tim Parker 

Polar Projects 

Cynthia 

Lawrence-Dever 

TA Ops 

Derry Webb 

Sensor Repair 

Lloyd Corothers 

Software/SysAdmin 

Denise Elvrum 

Permit Coordinator 

Brian Bonnett 

Polar Projects 

(Open) 

Warehouse Supervisor 

William Zamora 

Hardware 

Shane Ingate 

Sensor Testing 

Michael Love 

SysAdmin 

(Open) 

Software 

Alan Sauter 

Hardware/ 

Field Support 

Eliana Arias 

Data Specialist 

George Slad 


Greg Chavez 

Hardware 

(Open) 


Michael Johnson 

Hardware 

New Mexico Tech Student Assistants 

Hardware Group Sensors and Logistics Software Group TA Coordining Office 

Front Office Group 

Polar, Data, Accounting, 

and Shipping Group 

42

Derry Webb prepares a 

cart of broadband sensors 

for maintenance and 

repair in Socorro, NM. 

Marcos Alvarez prepares to 

install a broadband sensor, 

eastern Tibet. 

Crew work quickly to 

install a station on mount 

Erebus, Antarctica. 

Bob Greschke and Greg 

Chavez work together to 

develop new testing procedures, 

Socorro, NM. 

Bruce Beaudoin in 

Tibet, 2003. 

Mike Fort sets up a test 

on the Q330 work bench, 

Socorro, NM. 

Noel and Mingmar 

Sherpa at station 

in Namche Bazaar, 

Nepal for experiment 

HICLIMB. Photo by 

Anne Sheehan. 

Pnina Miller conducts a 

training session the use of 

the Reftek data loggers, 

Socorro, NM. 

Greg Chavez programs a 

broadband station, Paso 

Robles, CA. 

Jim Fowler installs 

an early TA station in 

California. 

assembly of Transportable Array and Flexible Array equipment. 

PASSCAL and AOF efforts are physically integrated 

to take advantage of numerous commonalities, and nine 

personnel at the PIC are presently supported by a combination 

of PASSCAL and EarthScope funding sources. The 

Transportable Array Coordinating Office (TACO) is an AOF 

group that responsible for logistical and siting support for 

Transportable Array field efforts. 

The PIC Director, Bruce Beaudoin, manages and reviews the 

activities of all NMT PIC staff, organized into six groups. 

The Director allocates fiscal and personnel resources on 

a daily basis, and coordinates longer-term budgeting and 

planning in association with the New Mexico Tech PI (Rick 

Aster) and IRIS staff. General PIC activities are coordinated 

by IRIS and implemented through the PIC PI, Rick Aster 

and Director, Bruce Beaudoin. The PI also acts as the principal 

point of contact with and representative of New Mexico 

Tech to collaborate with the director in budget, human 

resources, construction, student, education and outreach, 

employee evaluation, and general administration. 

General PIC activities are coordinated by the PASSCAL 

Program Manager with assistance from the Deputy Program 

Manager and implemented through the PIC PI and Director. 

The IRIS PASSCAL Program Manager, Jim Fowler, and 

Deputy PASSCAL Program Manager, Marcos Alvarez, are 

IRIS employees stationed in Socorro. The Program Manager 

is responsible for the PASSCAL Program as well as the 

overall IRIS/NMT operation. Marcos Alvarez oversees the 

Flexible Array component of the USArray and works with the 

Program Manager to optimize the overall instrument pool. 

43

The development of budgets, managing contracts, placing 

major equipment purchases and the tracking of expenditures 

are performed by the Program Manager and Deputy Program 

Manager. Additionally, initial communications with the PIs 

for instrument scheduling are conducted by the IRIS staff on 

site in Socorro. Transportable Array Manager Robert Busby, 

based in Massachusetts, coordinates with the overall AOF 

operations and remotely directs day-to-day TACO operations 

in association with TACO Manager, Steven Welch. 

Resource prioritization, aspects of instrument development 

and acquisition schedules, and annual budget recommendations 

for the PASSCAL Program and the PIC are provided 

by the IRIS PASSCAL Standing Committee (Appendix A), 

which meets semiannually and reports directly to the 

IRIS Board of Directors. 

PIC Operations 

PASSCAL management and staff are generally organized 

into supervisory and specialization groups. Five of these 

groups have supervisors reporting to the director: Hardware, 

Sensors and Logistics, Software, the Transportable Array 

Coordinating Office, and a Front Office. The Director 

directly supervises a sixth group that includes Polar, 

Data, and Accounting and Shipping activities. Because 

personnel are frequently working directly with PIs in the 

field, there is considerable overlapping expertise and a 

sharing of tasks across these groups. Many of the staff have 

distributed support reflecting overlapping responsibilities 

between PASSCAL and EarthScope Array Operations 

Facility operations. 

Hardware 

The Hardware Group overseen by Associate Director 

Mike Fort is responsible for quality assurance and maintenance 

of dataloggers and ancillary electronic equipment 

and power systems. 

Sensors 

Between the PASSCAL core program and EarthScope, 

PASSCAL supports over 1200 broadband and a nearly equal 

number of intermediate- to short-period seismometers. 

Sensor staff are responsible for both testing and repair, with 

three staff using the PIC’s two seismic piers essentially full 

time. Broadband sensor evaluation for new and returning 

seismometers is typically done in simultaneous batches of 

ten sensors per pier. Each pier test typically takes from three 

to five days, after which staff reviews the time series, both 

individually and in comparison with a reference sensor. A 

sensor that fails a pier test will evaluated by a repair staff of 

two, who have received special training from both of our 

principal broadband sensor vendors, Guralp and Streckeisen. 

Logistics and Shipping 

PASSCAL currently supports roughly 60 unique experiments 

per year worldwide. Logistics and shipping, overseen 

by Noel Barstow, typically handles all shipping arrangements 

from the PIC to the remote field in close association with the 

Hardware Group. Logistics and shipping staff work closely 

with PIs at all project stages to ensure that projects run 

smoothly and that science objectives are achieved. Services 

include shipping and customs documentation, carrier information, 

and general liaison activities with brokers and carriers. 

Shipping activities are also assisted by Jackie Gonzales 

under the direct supervision of the Director. 

Software 

The Software Group, supervised by Steve Azevedo, includes 

software developers and systems administrators. The group 

supports software development and implementation essential 

for processing PASSCAL data from raw field format to 

formats suitable for quality assurance, archival and scientific 

analysis. The staff also develops software for in-house hardware 

testing, programming, and quality-control tools, as well 

as supporting and distributing a PASSCAL software suite of 

data format-conversion, inventory control, metadata, data 

visualization, and quality-control tools that have overlapping 

uses both in-house and for the user community. 

44

Polar 

Approximately five to ten projects per year, predominantly 

funded by the NSF Office of Polar Programs, have recently 

been supported in polar regions. These projects typically 

require a level of support that is several times that of deployments 

in nonpolar environments. To ensure that these 

challenging projects achieve the highest level of success, 

PASSCAL has established a polar projects effort and has 

secured NSF MRI funds to support the unique instrumentation 

needs of a growing group of novel deployments, 

especially for OPP-funded research in Antarctica. At present, 

the PIC has two staff members dedicated to these efforts. 

This group is pursuing unique approaches to maintaining 

continuous operation throughout the polar winter, and to 

generally maximize data return in consideration of veryhigh-cost 

polar logistics. Specific efforts include extreme 

environmental enclosures, IRIDIUM satellite telemetry, 

low-temperature broadband sensors, and advanced power 

and battery systems. 

Accounting 

IRIS staff, the Director, and the PI use an accounting 

specialist, Elena Prusin, to facilitate budget monitoring, 

preparation, and reporting for PASSCAL and EarthScope 

funds and projects. 

Transportable Array Coordinating Office 

A staff of four under the overall guidance of Transportable 

Array Manager Bob Busby provides core site selection, 

scheduling, permitting, and general field coordination 

services for the 400-station EarthScope Transportable Array 

in close coordination with AOF staff at the PIC. 

Front Office 

A front office staff of two assists IRIS and NMT staff in the 

overall coordination of visitors, special events, visitor and 

employee travel, student employees, Web content updates, 

and purchasing. 

Data 

The Data Group provides direct user support for data 

archival and acts as the principal intermediary between the 

PI and the IRIS DMC during the archiving process to ensure 

proper archival of experiment data and metadata. PASSCAL 

data staff are expert in addressing special issues relevant to 

PASSCAL data sets and are thus critical to ensuring timely 

and accurate archival of data at the DMC. 

45

Trends and 

Recent Developments 

Throughout its history, PASSCAL has evolved and program 

emphases have changed in response to the demands of 

science and the scientific community. In this section, 

we explore some of this evolution, its impact on operational 

procedures and budget structure, and anticipate 

future directions. 

As initially conceived in 1984, PASSCAL was a basic community 

instrument resource facility, and acquiring and 

maintaining hardware were the primary activities. As the 

program has evolved, there has been increasing emphasis 

on training, field services, and software support. All of these 

activities place high demand on human resources, which 

has in turn increased pressure on balancing budgets to 

include both growth of the instrument pool and attendant 

expanded services. 

As IRIS completed the fourth five-year cooperative 

agreement with NSF (2001–2006), the PASSCAL facility 

approached the initial targets set in 1984 in terms of numbers 

of instruments and channels. In recent years, the budget 

profile for PASSCAL has shifted from growth of the pool 

through acquisition of new instruments to sustaining the 

pool through replacement of aging and damaged equipment. 

Unlike the USArray project where the focus of study lies 

within the North American continent, the PASSCAL 

program provides instruments for worldwide investigations. 

Most PI’ using the facility are funded by national organizations 

such as NSF and DOE to conduct studies driven by 

global tectonics. In particular, the majority of broadband and 

active-source (TEXAN) experiments have been conducted 

outside the US (Figure 36). This has been a consistent trend 

since the beginning of the program. In 2007, for example, 

out of a total of 18 broadband deployments, 11 were conducted 

overseas. In contrast, experiments using short period 

equipment have remained predominantly within the United 

States (Figure 36). Short period equipment is mainly used for 

regional or local seismicity studies often augmenting existing 

networks. All PASSCAL equipment types combined, the 

distribution of experiment are evenly split between foreign 

and domestic locations. 

Usage Trends 

Demand for instruments from the user community has 

exceeded the available resources. The PASSCAL pool has 

grown over the years to a complement of over 1000 digital 

recording systems (Table 1). What has changed is the 

character of the typical experiment. Through time, 

experiments have evolved to deploy larger numbers of 

instruments, reflecting the scientific need for higherresolution 

studies, and longer durations, reflecting the 

higher data return through capturing more earthquakes 

(Figure 36). Experiments using multiple instrumentation 

types have also increased. 

The average number of stations deployed in a typical broadband 

experiment now exceeds 30 (Figure 37a), and several 

deployments have been fielded in recent years that have 

exceeded 75. Instruments used for controlled-source studies 

(primarily the single-channel TEXANs) have also grown with 

the available pool now in excess of 2600 stations (including 

USArray equipment, Table 1). Interestingly, the number of 

broadband experiment starts has remained relatively level 

at around 10 experiments per year (Figure 37b). Another 

important trend observed in passive-source recording is the 

duration of an average experiment, which has increased gradually 

to around 2.5 years from approximately 1 year in the 

46

25 

20 

Foreign 

Domestic 

Broadband Experiments 

A 

35 

30 

PASSCAL Broadband Station Usage Patterns 

ave. no. sta. 

max. tot. exp. 

Number 

15 

10 

25 

20 

15 

5 

10 

5 

0 

1999 2000 2001 2002 2003 2004 2005 2006 2007 

Year 

0 

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 

25 

Foreign 

Domestic 

Short Period Experiments 

B 

30 

25 

expnt strts 

exp duration (mo) 

20 

20 

Number 

15 

10 

15 

10 

5 

5 

0 

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 

0 

25 

20 

1999 2000 2001 2002 2003 2004 2005 2006 2007 

Year 

Texan Experiments 

Foreign 

Domestic 

C 

35 

30 

25 

20 

15 

expnt strts 

max. tot. exp. 

Number 

Number 

15 

10 

5 

0 

45 

40 

35 

30 

25 

20 

1999 2000 2001 2002 2003 2004 2005 2006 2007 

Year 

Combined Experiments 

Foreign 

Domestic 

10 

5 

0 

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 

Figure 37. PASSCAL Broadband Sensor Usage Patterns. (A) Average 

number of stations per experiment (yellow) vs. total experiments 

deployed in a given year (purple). The average size of broadband 

experiments has steadily increased to approximately 30 stations. Due 

to the limited pool size, the number of new experiments fielded in a 

given year has declined with increasing experiment size. (B) Number 

of new experiment starts (blue) has stayed relatively constant through 

time while the maximum number of experiments deployed has 

gradually risen as a result of increased instrument pool. (C) Number 

of new experiment starts (blue) vs. average experiment duration. 

Deployment length (red) has gradually increased to an average of 

approximately 18 months. 

15 

10 

5 

0 

1999 2000 2001 2002 2003 2004 2005 2006 2007 

Year 

Figure 36. Distribution of experiment location as a function of equipment 

type (multichannel experiments not shown). The majority of 

broadband and TEXAN instruments are used in overseas deployments. 

This trend has been constant through time with increasing total 

number of experiments supported. The majority of short period experiments 

are conducted domestically. The graphs show concurrently 

conducted experiments. 

early 1990s (Figure 37c). This reflects community advances 

in higher-resolution studies incorporating large numbers of 

events. The time between experiments where the equipment 

is reconditioned and maintained at the PIC has always been a 

critical interval for optimal utilization of the PASSCAL pool. 

Larger experiments mean that large pulses of equipment 

need to be processed in a short amount of time, straining the 

multitasking personnel and other resources. 

47

600 

Broadband Instruments in the Field 

Future 

Commitments 

500 

Series1 

400 

Number of Instruments 

300 

200 

100 

0 

Figure 38. History of the short-period instrument pool. The reduction 

in short-period stations between 1995 and 2000 reflects retirement of 

three-channel, controlled-source experiments that were replaced by 

the TEXAN instruments in 2000. 

Overall, new projects each year have remained constant 

while the size and duration (and number of PIs) for a typical 

experiment continues to grow. In the past, PASSCAL 

has been able to manage these trends with an increasing 

yearly inventory (Figure 38). If the total equipment inventory 

reaches a stable level, the net effect will manifest itself 

predictably into longer wait times for instruments. This 

trend can be seen in Figures 39 and 40, where the cumulative 

number of experiments and future equipment requests are 

plotted versus the total inventory of equipment. 

Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- Jan- 

90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 

Figure 39. PASSCAL broadband experiment history. Histogram of 

all experiments through time plotted as a total of stations. Current 

broadband inventory is approximately 460 sensors. Average wait time 

for equipment has remained constant at approximately 2.5 years. 

Actual experiments are plotted before the current time, equipment 

requests after 2007. 

available to fund field programs. Indirectly, the pressure 

of wait times may also influence the number of proposals 

submitted. A reasonable delay between the funding decision 

and the start of field programs can sometimes be an 

advantage in planning and logistical preparation, but significant 

delays are problematic, especially for young faculty, 

students, and postdocs. 

PASSCAL Broadband Experiments 

PASSCAL Broadband Experiments 

The “wait time” for instruments—the time 

between NSF’s or some other agency’s decision 

to fund a proposal and when the full 

complement of instruments are available for 

deployment—has been a constant source of 

concern for the user community. As noted 

above, in spite of increasing numbers of 

instruments, the general growth in experiment 

size has meant that the broadband pool 

remains in continual use—and there has not 

been a decrease in wait time. For most of 

the lifetime of PASSCAL, the wait time has 

remained at 2–2.5 years. The length of the 

wait time depends on a complex interaction 

among the number of instruments available, 

the desired size of arrays, the number of 

proposals funded, and the level of resources 

Number of Instruments 

Figure 40. Time history of PASSCAL broadband experiments. Each experiment is one 

line. The earliest experiments are in the front; recent and proposed experiments are 

in the back. The size of each box shows experiment duration (length on the time axis) 

and number of instruments (vertical axis). The trend toward longer experiments (wider 

boxes) with more instruments (higher boxes) is clearly seen. 

48

Box 3. PASSCAL Education and Outreach 

PASSCAL-supported projects often incorporate graduate 

students (and sometimes undergraduates) in preparation, 

deployment, data collection, and science analysis, 

publication, and thesis efforts. For example, during 2007, 

new or ongoing student-associated projects included 

efforts in Antarctica, many sites in the western United 

States, Montserrat, Argentina, Venezuela, and Vietnam. 

Additionally, PASSCAL annually supports numerous 

equipment requests for purely educational efforts. The 

majority of these requests are for short-term use of the 

cabled multichannel systems for university classes and 

educational field programs (e.g., the Summer of Applied 

Geophysical Experience [SAGE] program) supported by the 

US Department of Energy and NSF. 

Since 2006, in association with IRIS E&O, the PIC 

and NMT host an annual orientation week for the IRIS 

Intern Program (an NSF-funded Research Experience for 

Undergraduates [REU] initiative). During the orientation, 

IRIS interns (typically 10) from a broad range of backgrounds 

participate in field trips and lectures lead by IRIS 

E&O staff, and by NMT and other IRIS community faculty. 

The agenda includes seismology “state-of-the-science” 

talks, elements of instrumentation and data analysis, 

geological and geophysical field trips, PASSCAL instrumentation 

data acquisition exercises, and a career discussion 

panel of professionals from government, academia, and 

industry. The orientation is designed to provide a common 

introduction to the field prior to the students’ departure for 

their summer intern research at widely scattered IRIS institutions 

and field sites. Since 1999, PASSCAL has also supported 

a Summer Graduate Intern at the Instrument Center. 

PASSCAL Graduate Interns acquire a detailed knowledge 

of many aspects of seismographic instrumentation and data 

collection by working with PIC staff for up to 12 weeks in 

a wide variety of efforts, both at the PIC and in the field. 

To participate in outreach at the local level, IRIS supports 

an annual science award to a deserving student at Socorro 

High School. 

PIC staff and NMT faculty frequently gives tours and overview 

talks for diverse groups, including NMT graduate and 

undergraduate classes, groups on earth science field trips to 

the region, visiting administrators, lawmakers, and foreign 

colleagues (e.g., a 2007 delegation of Chinese colleagues 

on a planning trip for establishing a PASSCAL-like facility 

in China). The PIC is also used several times per year for 

IRIS and partner science groups for science, review, and 

facility meetings. 

49

ALLpeople,instrmt, & ratio 

All programs, 1988 -2006; Total Stations, People, Ratio 

4500 

4000 

Personnel Trends 

3500 

DOE DAS replacement 

140 

120 

ALLpeople,instrmt, ALLpeople,instrmt, 

& & 

ratio 

ratio 

Faced with 3000 the trend of larger experiments and bigger 

inventories, 

2500 

PASSCAL has been able to maintain a high 

level of service, with only minor increases in staff, by 

2000 

PIC 

becoming more efficient in all aspects consolidation of the operation, most 

1500 

fundamentally by consolidating PASSCAL operations to a 

1000 

single Instrument Center in 1998. Advances in warehousing 

USArray begins 

techniques, 

500 

testing procedures, automated processing tools, 

and improved 0 facilities have all contributed to our ability to 

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1999 2000 2001 2002 2003 

keep up with the increased workload. Nevertheless, Year there 

have been inevitable stresses on the staff, as the personnel 

Page 1 

levels have only slightly increased as the number of instruments 

has steadily risen. For example, in the early 1990s, the 

personnel-to-instrument ratio was approximately 35 instruments 

per person, with a staff of approximately 13. In 2008, 

there are approximately 31 staff positions with a ratio of 

roughly 130 instruments per person (Figure 41). These ratios 

include USArray equipment and personnel, but do not differ 

substantially if only PASSCAL personnel and equipment are 

considered. One present effect of this increased workload is 

a reduction in our ability to advance user support in such 

important areas as documentation, training resources, and 

new instrumentation development. 

Total Instruments 

4500 

4500 

80 

4000 

4000 

60 

3500 

3500 

3000 

40 

3000 

2500 

2500 20 

2000 

2000 

0 

1 2 3 4 5 6 7 8 9 10 11 

1998 

12 13 14 15 16 17 

2004 

18 

2005 

19 

2006 

20 

1500 

1500 



100 

1000 

1000 

500 

500 

number 

All All 

All 

programs, programs, 

1988 1988 

-2006; -2006; 

Total Total 

Stations, Stations, 

People, People, 

Ratio 

Ratio 

Year 

Instruments 

People 

Instr/People 

PIC 

PIC 

consolidation 

consolidation 

DOE DOE 

DAS DAS 

replacement 

replacement 

USArray USArray 

begins 

begins 

0 

0 

0 

1988 0 

1 

1989 10 11 12 13 14 15 16 17 18 19 1988 

1 

21989 1990 

2 

3 

1991 1992 

1990 3 

41991 4 

51992 5 

61993 6 

71994 1995 1996 

71994 8 1995 1996 

8 

9 

9 

10 

1997 

10 

1997 11 

1998 

11 

1998 12 

1999 

12 

1999 13 

2000 

13 

2000 14 

2001 

14 

2001 15 

2002 

15 

2002 16 

2003 

16 

2003 17 

2004 

17 

2004 18 

2005 

18 

2005 19 

2006 

19 

2006 

20 

Year 

Year 

140 

140 

120 

120 

100 

100 

Figure 41. PIC personnel. Instruments and ratio for all programs, 

1988–2006. The PASSCAL equipment inventory Page has dramatically 

Page 

1 

1 

increased since 1998 while total personnel levels have risen only 

slightly. Currently, the instrument-to-person ratio is near 130, up from 

35 in 1998. This plot shows all PASSCAL and USArray personnel and 

equipment but does not include TACO or contracted personnel. 

80 80 

80 

60 60 

60 

40 40 

40 

20 20 

20 

number 

number 

Year 

Year 

Instruments 

Instruments 

People 

People 

Instr/People 

Instr/People 

Broadband Sensors—Protecting Past Investments 

A powerful trend during the 20-year lifetime of IRIS and 

PASSCAL has been the increased use of broadband instruments. 

Modern computers make it possible to record and 

analyze large quantities of long-duration, high-sample-rate 

data, resulting in increased interest in full waveforms and 

long seismograms, and new seismological methodologies 

have opened up that exploit the full bandwidth of these 

data. Small, relatively low-power feedback designs provide 

stable sensors that can be easily transported and installed 

in relatively simple vaults. The feedback sensors used in 

these experiments, however, are inherently more complex, 

fragile, and higher power than the passive short- or longperiod 

sensors. Note that the PASSCAL broadband sensors, 

the Streckheisen STS2 and the Guralp CMG3T, were not 

inherently designed to be portable in the frequent redeployment 

sense that they are now used by PASSCAL, but were 

instead designed primarily as observatory instruments for 

infrequent transport and long-term installation. However, 

the majority of the broadband sensors purchased throughout 

the buildup of the PASSCAL inventory are still in use today. 

In a large part, that so many of these sensors are still in use is 

the result of careful maintenance and repair by PIC staff, and 

commitment of resources to sensor testing and repair. The 

median age of a PASSCAL broadband sensor is now 10 years 

(Figure 42). Some of these older sensors are now beginning 

to fail and are no longer reparable. Additional resources per 

sensor are furthermore commonly required to replace and 

repair these older instruments. 

PASSCAL and other national and international groups 

have worked closely with a small number of commercial 

companies to develop sensors with higher reliability and 

50

lower power that will be more appropriate for rugged 

field programs and long-term deployments. Both new 

manufacturing techniques and fundamental new designs 

have been explored. In spite of some refinements in design 

and improvements in the manufacturing process (resulting 

in modest improvements in ruggedness and reliability), 

the approximately 30-year-old fundamental mass-springfeedback 

design has not been changed. There may be new 

design options on the horizon for rugged, short-period (few 

seconds) sensors, but it appears unlikely that there will be 

significant breakthroughs in the intermediate and longperiod 

range (tens to hundreds of seconds). In this environment, 

PASSCAL will continue to explore the best means 

to maintain and repair the current designs and work with 

PIs to develop procedures for proper care of sensors during 

shipping and in the field. 

BB Sensors 

80 

70 

60 

50 

40 

30 

20 

10 

0 

Broadband Sensor Purchase History, NSF & DOE 

Median Age of BB Sensor in 2007 = 10 years 

1989 

1990 

1991 

1992 

1993 

1994 

1995 

1996 

1997 

1998 

Year 

DOE award 

1999 

2000 

2001 

2002 

2003 

2004 

2005 

Figure 42. Broadband sensor purchase history from NSF and 

DOE funds. The median age of the PASSCAL broadband sensor in 

2007 was 10 years. Most broadband sensors purchased are still in 

service today. 

2006 

2007 

Future Trends 

The composition of the PASSCAL instrument pool and its 

modes of field and software support evolve as new scientific 

opportunities arise and as advanced technologies develop. 

Sustaining state-of-the art instrumentation thus entails 

adopting new technologies, notably in communications, 

power sources, and sensors, as they become available and 

pursuing the development of increasingly lower-power and 

lower-cost instrumentation. 

Recent experience with the USArray has demonstrated 

that real-time data recovery increases data quality and data 

return while optimizing field resources. However, the cost for 

operating a real-time network is associated with significant 

service fees and data center infrastructure that still precludes 

its use in the typical PASSCAL experiment. The technology is 

continuing to progress, and we expect real-time communications 

will be increasingly feasible for more experiments in the 

near future. The funding of recurring communications fees is 

an issue that will need to be worked out with PIs and NSF. 

The new generation data loggers that comprise the PASSCAL 

pool (REF TEK RT130s and Quanterra Q330s) are all 

equipped with modern communications protocols. These 

systems have been configured to work well with modern 

radio, cell phone, IRIDIUM, and VSAT communications 

systems. Although setting up a real-time seismic network 

in a foreign country is still very challenging, worldwide 

communications are advancing and becoming standardized 

so rapidly that we expect that real-time communications for 

overseas projects will also be realistic in the near future. But, 

here again, the budgeting of communications costs will be an 

issue. We are also watching with interest several initiatives in 

the community for “mote” or other small-scale, self-organizing 

sensor networks that may eventually offer other robust 

telemetry options in smaller scale experiment situations 

such as volcano or glacier seismology. 

A promising integration into the PASSCAL mode of operations 

is the development of power and telemetry systems 

suitable for Antarctic deployments. The use of a combined 

solar, wind, and lithium battery system matched with a verylow-power 

seismic system is currently being implemented 

in two deep-field projects. The knowledge and experience 

acquired in support of deployments in such extreme environments 

permeates into the rest of the program, and helps 

to improve support throughout. 

51

Budget 

The primary source for PASSCAL core funding has been 

through a series of five-year cooperative agreements between 

IRIS and the National Science Foundation. Figure 43 shows 

the overall IRIS core (without EarthScope) funding. Each 

of the three major programs—PASSCAL, DMS, and GSN— 

operate with a base budget of about $3.2M. This funding 

has remained level over the last several years. A significant 

enhancement of over $9M to the PASSCAL budget has come 

from special Congressional appropriations coordinated 

through the Department of Energy between 2001 and 2005. 

This money was targeted for the replacement of the original 

data acquisition systems. EarthScope and USArray funding 

come through a separate 7.0 cooperative agreement, and 

includes separate budgets for Major Research Equipment 

and Operations and Maintenance. 

Figure 44 shows 

6.0 

a breakdown of core PASSCAL spending 

3.0 

by category. 5.0 With the exception of the money spent on 

2.0 

hardware, the spending levels for the rest of the program 

Millions of Dollars 

7.0 

4.0 

are relatively constant. The 

1.0major non-equipment items in 

3.0 

the budget are subawards. 0Currently, there are two major 

2.0 

subawards: one to the UTEP and one for the PIC at NMT. 

1.0 


6.0 

5.0 

4.0 

PASSCAL Total Funding 

FY97 FY98 FY99 

0 

The PIC award FY97 to NMT FY98 provides FY99 salary support for 13 fulltime 

employees. Included within the overhead structure 

of this award is the provision and maintenance of office, 

laboratory, and warehouse facilities. Other basic services, 

such as administrative support and Internet bandwidth, are 

supported through this award. The yearly costs associated 

operating the core instrument center stabilized markedly 

after the consolidation of instrument centers from Lamont 

and Stanford to NMT in 1998 (Figure 45). For fiscal year 

2007, the NMT PIC award was $1.637M. 

The UTEP award provides support for approximately 

1.2 full-time employees. UTEP has title to 440 singlechannel 

TEXAN instruments purchased by the state of 

Texas. This subaward ensures PASSCAL user community 

access to these instruments and thus more than doubling the 

number of PASSCAL TEXAN instruments. For fiscal year 

2007, the UTEP award was $199K. 




IRIS Funding (Core Cooperative Agreements) 

EAR-0004370 

EAR-0552316 

5-Year Funding Total: 

2-Year Funding Total: 

$75,578,575 

$23,813,768 

18.0 

$16,214,83 $16,357,79 

$15,812,28 

16.0 

$14,832,93 

14.0 

$12,360,72 

$12,325,24 

$11,488,51 

12.0 

10.0 

8.0 

6.0 

4.0 

2.0 

0 

FY02 FY03 FY04 FY05 FY06 FY07 FY08 

7.0 

6.0 

5.0 

Figure 43. 

Other 

FY00 FY01 FY02 FY03 FY04 FY05 4.0 FY06Subawards 

FY07 FY08 

Salaries+Fringe 

3.0 

2.0 

FY00 FY01 FY02 FY03 FY04 FY05 FY06 FY07 FY08 


Figure 44. 

Figure 45. 

Materials & Supplies 

Equipment 

Publications 

Participant Support 


Travel 

Consultants 

Materials & Supplies Other 

Equipment 

Subawards 

Publications 



Travel 

Consultants 

PASSCAL 

DOE 

GSN 

DMS (incl. O/H) 

Management Fees 

E&O 

H2O 

G&A 

DC OFFICE O/H 

OTHER 

COMM. ACT. 

1.0 

0 

FY97 FY98 FY99 FY00 FY01 FY02 FY03 FY04 FY05 FY06 FY07 FY08 

Instrument Center Costs (PASSCAL Budget) 

2.5 

Instrument Center Consolidation 

2 

1.5 

1 

.5 

0 

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 

Year 

Materials & Supplies 

Equipment 

Publications 


Travel 

Consultants 

Other 

Subawards 


52

Appendix A 

PASSCAL Standing Committee and Past Chairs 

Current Members 

Alan Levander (Chair)......... Rice University 

Richard Allen......................... University of California, Berkeley 

Matthew Fouch...................... Arizona State University 

Tom Pratt................................ University of Washington 

Stéphane Rondenay.............. Massachusetts Institute of Technology 

Arthur Rodgers..................... Lawrence Livermore National Laboratory 

Ray Russo............................... University of Florida 

George Zandt......................... University of Arizona 

Past Chairs 

Larry Braile............................ Purdue University (1987–1990) 

Anne Trehu............................ Oregon State University (1991–1992) 

Gary Pavlis............................. University of Indiana (1993–1995) 

Anne Meltzer......................... Lehigh University (1996–1998) 

Roy Johnson........................... University of Arizona (1999–2001) 

David James........................... Carnegie Institution of Washington (2003–2005) 

Alan Levander....................... Rice University (2006–2008) 

53

Appendix B 

Policy for the Use of PASSCAL Instruments 

September 12, 2006 

Introduction 

Portable field recording equipment and field computers 

purchased by the PASSCAL Program are available to any 

research or educational institution to use for research 

purposes within the guidelines established in this document. 

The intent of these guidelines is to establish the procedures 

to enable investigators to request the instruments, to let 

them know what requirements and responsibilities are 

incurred in borrowing the equipment and to know when and 

how the decisions on instrument allocation will be made. 

support which is provided. Only through your continued 

support and feedback will IRIS be able to develop and 

expand the services it provides for seismological research. 

PASSCAL publishes an inventory of all of its equipment 

through the IRIS World Wide Web site (http://www.iris. 

edu). This inventory includes all data loggers, sensors, field 

computers and major ancillary equipment. A description 

of the capabilities of the various pieces of equipment are 

available with the inventory as well as a copy of the current 

instrument schedule. 

The efficient use of the instruments will require close 

cooperation among all of the parties involved. The Principal 

Investigator is encouraged to contact the PASSCAL Program 

Manager about any planned experiment during the proposal 

development stage in order to determine if there are any 

problems in operating the equipment in the environment 

called for in the experiment. It is also important for everyone 

to know of possible schedule conflicts as early as possible. 

Open communications will allow the development of alternative 

plans early in the scheduling process. 

The PASSCAL instrumentation and associated services 

are provided, without charge, as part of the facility 

support developed by IRIS through funding from the 

Instrumentation and Facilities Program, Earth Sciences 

Division, National Science Foundation, with additional 

equipment provided through the Air Force Office of 

Scientific Research, the Office of Nonproliferation Research 

& Engineering of the Department of Energy and the Office 

of Basic Energy Sciences of the Department of Energy. As a 

community resource, IRIS and NSF rely on the individual 

PIs to conform to a limited number of rules and conditions 

related to the use of PASSCAL instruments, to treat the 

instruments with care and respect, and to acknowledge the 

Procedure for 

Borrowing Instruments 

Any research or educational institution may request the 

use of the equipment for experiments of scientific merit. 

The initial request will be submitted to the IRIS via the 

Worldwide Web using: 

• http://www.iris.edu 

The initial request should be sent to IRIS at the time the 

proposal is sent to the funding agency. 

Each request will as a minimum contain the following 

information: 

1. A short description of the experiment to be conducted; 

including any unusual field conditions which may be 

encountered; 

2. The location of the experiment (latitude - longitude as 

well as an estimate of the aerial extent); 

3. Starting and ending dates of the experiment along with 

information on any extenuating circumstances which may 

make it impossible to slide the date forward or backward; 

54

4. The types and number of pieces of equipment requested 

for the experiment; 

5. An estimate of the amount of data to be gathered and 

archived; 

6. A notification of any special support which may be 

required; 

7. The name of the funding agency and status of the funding 

support; and 

8. A mailing address, email address, phone and fax numbers 

for the designated contact person for this experiment. 

Scheduling 

Experiments which receive funding after January 1 will be 

entered into the schedule so as not to interfere with previously 

approved experiments. Requests can be made for 

instruments at any time during the year, and they will be 

made available to users as the schedule permits. If an experiment 

can not go in its allocated slot for some reason it goes 

to the back of the line unless: 

1. The PI’s in affected experiments voluntarily agree to delay 

or modify the experiment schedule, or 

2. The applicable NSF and/or DOE Program Manager(s) 

decides that the delayed experiment takes priority over 

one of their subsequent experiments. 

The schedule is determined in the fall of each year for the 

next year. If conflicts exist, a committee of impartial members 

from the PASSCAL Standing Committee along with 

any interested representatives from the National Science 

Foundation will meet to make the final determinations. Only 

experiments with established funding will be entered into 

the schedule. Priorities will be set in the following order: 

1. Programs funded by the Earth Sciences Division of 

NSF or by the Office of Nonproliferation Research & 

Engineering of the Department of Energy; 

2. Programs funded by other divisions of NSF; 

3. Programs funded by other US government agencies; and 

4. Other programs. 

All other conditions being equal, the highest priority will 

go to experiments with the earliest funding dates, then the 

earliest request dates. The goal of the scheduling is to optimize 

the use of the instruments, and accommodate as many 

experiments as possible. Therefore, it is sometimes necessary 

to negotiate with the PI the exact type and number of instruments 

or to move the scheduled time of the experiment. 

IRIS will publish the schedule for the coming year as soon 

as the committee recommendations are completed and 

approved by the President of IRIS. Once the experiment 

has been scheduled, the PI will be contacted to work out 

the details about the exact type of equipment, the ancillary 

equipment and the field support personnel who will be 

assigned to the experiment. At this point the PI will also 

have to start working with PASSCAL to provide information 

to the Data Management System about the experiment and 

the data delivery. 

55 

Principal Investigator 

Commitments 

Investigators borrowing instruments will be required to meet 

the following conditions: 

1. Copies of all data sets acquired with the instruments will 

be made available to the IRIS Data Management Center 

in accordance with the PASSCAL Data Delivery Policy. 

The delivery of the data is considered the equivalent of 

delivery of a final report. 

2. The PI and key experiment personnel are required to 

attend an Experiment Planning Session at the PASSCAL 

Instrument Center. At this session they will work with 

the PASSCAL personnel to finalize the operational plans 

for the experiment and receive training on the recording 

instruments and the field computers. This is necessary 

even for a repeat users, as equipment and software are 

being upgraded continuously. 

3. Experiments should budget to pay travel expenses for 

personnel from the PASSCAL Instrument Center to 

accompany the equipment to the field to insure that the 

equipment is functioning properly and to provide additional 

in-field training to the experiment personnel. This 

personnel support, which can be requested by the PI or at 

the discretion of PASSCAL, is intended to be short-term 

support to insure that the experiment can start collecting 

useful data in a timely manner. Experiments with very 

large numbers of instrument (> 100) or other special

equirements should be prepared to pay for more than 

one person to come to the field. The final arrangements 

for support will be negotiated after the experiment is on 

the schedule. 

4. The experiment will be responsible for all shipping costs 

and duties which may be incurred in getting the equipment 

to and from the field site. The PASSCAL Instrument 

Centers provide advice, documentation and other support 

in this effort. For international experiments the PI is 

responsible for making all shipping and customs arrangements 

and paying any fees involved. 

5. The PI is responsible to see that the equipment is returned 

to the appropriate instrument center on the date specified. 

In the case of foreign experiments, the PI will have at least 

one person in country overseeing the customs and shipping 

efforts until the equipment has cleared customs and 

is in transit back to the US. 

“The instruments used in the field program were provided 

by the PASSCAL facility of the Incorporated Research 

Institutions for Seismology (IRIS) through the PASSCAL 

Instrument Center at New Mexico Tech. Data collected 

during this experiment will be available through the 

IRIS Data Management Center. The facilities of the 

IRIS Consortium are supported by the National Science 

Foundation under Cooperative Agreement EAR-0004370 

and by the Department of Energy National Nuclear 

Security Administration.” 

9. The Principal Investigator must sign and return a PI 

Acknowledgement Form such as the one attached below. 

Please provide IRIS with copies of any publications related to 

your experiment. 

IRIS Commitment 

6. The investigators will be responsible for loss or damage 

that occurs as a result of negligence or improper handling 

of the equipment. IRIS will carry an insurance policy on 

all of the equipment but this is intended to cover major 

losses due to theft or accident. 

7. Immediately after the field work has been completed, 

the PI will submit a short report summarizing the field 

portion of the experiment. This report will contain the 

following: 

• A short description of the completed field experiment; 

• A list of station locations; 

• A summary of the data collected as well as any unusual 

events which may be included; 

• A description of problems encountered with either the 

hardware or the software furnished by the PASSCAL 

program; and 

• Recommendations for further improvement in the 

facility. 

8. Acknowledgment - In any publications or reports resulting 

from the use of these instruments, please include the 

following statement in the acknowledgment section. You 

are also encouraged to acknowledge NSF and IRIS in any 

contacts with the news media or in general articles. 

IRIS/PASSCAL will provide the following services to the 

experiment: 

1. The equipment will be ready to ship from the instrument 

center on the date specified. 

2. Appropriate technical support as negotiated with the PI 

during planning. IRIS will contract for the salaries for the 

support personnel, but it is up to the experiment to pay 

any travel costs for these personnel. 

3. Maintenance on units which malfunction in the field. 

IRIS will attempt to repair or replace the equipment as 

quickly as possible. 

4. Computer support in the form of a full capability 

field computer which will be located at the PASSCAL 

Instrument Center. This system, which may be in addition 

to the field computer provided for use during the field 

experiment, is to help investigators who do not have 

access to a field computer to get the data into formats 

acceptable to the Data Management Center. 

5. IRIS will provide system support to help investigators 

install IRIS-developed non-proprietary field computer 

software on the PI’s own compatible systems. 

This policy is effective as of May 12, 2003 and is subject to 

change and revision as needs dictate. 

56

Appendix C 

PASSCAL Data Delivery Policy 

November 18, 2004 

The equipment in the PASSCAL facility represents a significant 

community resource. The quality of the data collected 

by this resource is such that it will be of interest to investigators 

for many years. In order to encourage the use of the 

data by others and thereby make the facility of more value to 

the community, IRIS policy states that all data collected by 

instruments from the PASSCAL Facility should be submitted 

to the Data Management Center so that they can be accessed 

by other interested investigators after the proprietary period. 

This policy outlines the guidelines for data submission. IRIS’s 

policy is that delivery of data to the DMC is an obligation 

of the PI. It is important to IRIS that the PI acknowledges 

this obligation and meets it within the required time frame. 

Failure to complete this requirement not only deprives the 

community of a valuable data resource, but also may jeopardize 

future requests to borrow IRIS equipment. 

IRIS expects data delivery while the experiment is in the 

field (for long term deployments), or immediately at the 

conclusion of the field deployment. The data and Data 

Report will remain confidential for a period of 2 years 

after the end of the fieldwork. 

Data Report 

The Data Report is not intended as a formal technical paper 

but it should contain enough information to allow someone 

to work with the data. If possible the report should be in a 

widely accepted electronic format such as RTF or PDF. Any 

figures can be included as Postscript files. The following 

types of information should be included: 

• A short description of the experiment; 

• A list of stations occupied along with coordinates and a 

short description of the sites; 

• A description of the type of calibration information 

acquired; and 

• For non-SEED data a description of the data archive 

volume. 

The Data Report and completed Demobilization Form are 

due immediately after the completion of the experiment. 

Data 

The actual format of the data and the amount of data depend 

upon the type of experiment. Most PASSCAL experiments 

fall into one of the following categories: Broadband, short 

period or reflection /refraction. The first two are passive 

source experiments while the third utilizes active sources. 

Broadband (Continuous Data) 

The data from broadband experiments (that is experiments 

collecting continuous data from broadband sensors at 

sample rates less than or equal to 40 sps) can be used in a 

variety of different investigations. Therefore, it is in the best 

interest of the community to archive these data for easy 

access by the seismology community. Each PI conducting a 

broadband experiment will utilize the PASSCAL database or 

equivalent software to provide all of the data collected to the 

DMC for archive in SEED format. It is expected that the PI 

will ship the data to the DMC on a continuing basis during 

the experiment as soon as timing and other corrections 

are made and that the final data will arrive shortly after the 

experiment is over. The DMC will make the data available 

57

only to the PI or his designated representative for a period of 

two years after the completion of the experiment. After that, 

the data will be made available to the public. 

be provided by the DMC to the PI. The PI can share the 

password with anyone he/she wishes. The PI will be notified 

when anyone registers for access to a proprietary dataset. 

Short Period (Triggered) 

Short period experiments are generally different from broadband 

experiments in both the amount and the bandwidth 

of the data they produce. Short period sensors are generally 

run at higher sample rates than broadband sensors, and the 

ability to record low frequency signals is very limited. As 

the short period data are typically recorded in a triggered 

mode, their principal archive will be as event data. The time 

windows should be long enough to include a reasonable 

amount of pre-event noise signal as well as all of the significant 

seismic phases for the event. As above, the data should 

be delivered to the DMC for distribution in SEED format. 

The PASSCAL field computers have the necessary software 

for this delivery. 

Reflection/Refraction 

Reflection/Refraction experiments differ from the above 

experiments in that they nearly always involve active 

sources. The receivers are typically arranged in regular one 

or two-dimensional arrays. The accepted data format for 

these active source experiments is conventional SEG-Y 

format. The data should include all of the necessary information 

on the geometry of the experiment (metadata) and they 

should be corrected for all known timing problems. 

Information about the experiment such as station locations 

and characteristics will be made publicly available during the 

experiment, only waveform data will be limited in distribution 

during the proprietary period. 

All passive experiments with five or more stations will 

designate at least one station as and “open station”. The 

data from the “open station/s” will be made available to 

the public immediately upon being archived. 

Support Available from IRIS 

Every field computer has the software necessary to accomplish 

the data delivery task, and the PASSCAL Instrument 

Center has personnel who can provide assistance to the PI 

during and after the experiment. The Instrument Center also 

has software, computers, and large disk systems available for 

use by the PI. The Data Management System has additional 

facilities and support available to the PI. The PI is encouraged 

to utilize these resources at all stages of the work. In all 

cases, however, the ultimate responsibility for delivery of the 

data rests with the Principal Investigator. The PI must ensure 

that adequate resources are budgeted to accomplish this task. 

Non-Standard 

There will always be some experiments that do not fit 

directly into one of the above categories. In those cases the 

exact form of the data delivery will be negotiated between 

the PI, the IRIS Data Management System and PASSCAL. 

Proprietary Data 

Data of all types should be delivered to the DMC, in the 

appropriate format, as soon as possible and normally 

well before the general release of the data. The DMC will 

only allow access to the waveforms to the PI and others 

designated by the PI. Access will be by password that will 

A PASSCAL data submission is not considered complete 

until both the PASSCAL and DMS Program Managers certify 

that the information contained in the report is sufficient 

to allow other members of the community to utilize the data. 

IRIS will not certify that it has received data from any PI 

until the data submission is deemed usable. 

This policy is effective as of November 18, 2004 and is 

subject to change and revision as needs dictate. For updated 

versions of the policy and additional information on data 

delivery see the PASSCAL and DMS pages on the IRIS web 

site (http://www.iris.edu). 

58

Appendix D 

PI Acknowledgement 

PI ACKNOWLEDGMENT 

May 12, 2003 

The undersigned (User) acknowledges that User will be receiving Government-owned equipment from 

Incorporated Research Institutions for Seismology (IRIS) pursuant to the PASSCAL Program: 

This equipment is being made available to User, free of charge, as a scientific resource. The equipment 

will be treated with care and returned in an undamaged condition at the specified return date, to the 

appropriate Instrument Center. User will be solely responsible for the use and care of the equipment 

until its return, including all shipping and handling costs and fees. User has read and agrees to abide by 

the conditions of the Data Delivery Policy and the Instrument Use Policy including proper 

acknowledgement of support in all publications. 

PASSCAL Instrument Centers will upon request provide advice, documentation and other support, and 

at User’s expense will send personnel to the field to insure that the equipment is functioning properly. 

Date: 

Principal Investigator (Printed) 

Signed 

Relevant policies: 

Instrument Use Policy (5/12/03) 

Data Delivery Policy (5/12/03) 

Return to: 

Jim Fowler 

IRIS/PASSCAL – NMT 

100 East Road 


(505) 835 5072 ph 

(505) 835 5079 fx 

Institution 

59

Appendix E 

PASSCAL Instrument Use Agreement 

Principal Investigator: _________________________ 

Experiment: ________________ 

PASSCAL Instrument Use Agreement 

Portable field recording equipment, field computers and other associated equipment purchased by the PASSCAL 

Program are being made available to the experiment referenced above. In return for the use of this equipment, the 

Principal Investigator (PI) is expected to adhere to the following conditions with respect to the operation, care and 

disposition of the equipment and data obtained: 

1. Copies of all data sets acquired with the instruments will be made available to the IRIS Data Management 

Center in accordance with the PASSCAL Data Delivery Policy. This policy can be found through the IRIS web 

site (http://www.iris.edu); 

2. The PI and key experiment personnel are required to have proper training on the recording instruments and the 

field computers; 

3. The PI is responsible for all travel expenses for personnel from the PASSCAL Instrument Center who 

accompany the equipment to the field; 

4. The experiment will be responsible for all shipping arrangements, costs and customs duties which may be 

incurred in getting the equipment legally to and from the field site. The PASSCAL Instrument Centers provide 

advice, documentation and other support in this effort; 

5. The PI is responsible to see that the equipment is returned to the instrument center on the date specified. In the 

case of foreign experiments, the PI will have at least one person in country overseeing the customs and shipping 

efforts until the equipment has cleared customs and is in transit back to the US; 

6. The investigators will be responsible for appropriate care and handling of the equipment; 

7. The PI is responsible for obtaining all permits (Federal, State, local and private), prior to installation necessary 

for the lawful operation of the equipment; 

8. Immediately after the field work has been completed, the PI will submit an Experiment Evaluation Form 

(http://www.passcal.nmt.edu/forms/EvalForms.html) summarizing the field portion of the experiment; and 

9. Following completion of data archiving with the DMC, the PI will submit a Data Evaluation Form 

(http://www.passcal.nmt.edu/forms/EvalForms.html) summarizing the data archiving portion of the experiment. 

Acknowledgment - In any publications or reports resulting from the use of these instruments, please include the 

following statement in the acknowledgment section. You are also encouraged to acknowledge NSF and IRIS in any 

contacts with the news media or in general articles. 

"The instruments used in the field program were provided by the PASSCAL facility of the Incorporated Research 

Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. Data collected 

during this experiment will be available through the IRIS Data Management Center. The facilities of the IRIS 

Consortium are supported by the National Science Foundation under Cooperative Agreement EAR-0004370 and by the 

Department of Energy National Nuclear Security Administration." 

The undersigned ( ________ ) acknowledges that _________ will be receiving Government-owned equipment from 

Incorporated Research Institutions for Seismology (IRIS) pursuant to the PASSCAL Program: This equipment is being 

made available to _________ , free of charge, as a scientific resource. The equipment will be treated with care and 

returned in an undamaged condition at the specified return date, to the appropriate Instrument Center. ________ will 

be solely responsible for the use and care of the equipment until its return, including all shipping and handling costs 

and fees. _________ has read and agrees to abide by the conditions of the 

http://www.passcal.nmt.edu/information/Policies/data.delivery.html and the Instrument Use Policy including proper 

acknowledgement of support in all publications. 

PASSCAL Instrument Centers will upon request provide advice, documentation and other support, and at _________ 

expense will send personnel to the field to insure that the equipment is functioning properly. 

Relevant policies: 

Instrument Use Policy (9/12/06) 

Data Delivery Policy (11/18/04) 

60

Appendix F 

PASSCAL FIELD STAFFING POLICY 

August 23, 2006 

PIC Staffing Support for 

Field Operations 

PIC Staff Responsibilities 

in the Field 

PIs may request PASSCAL Instrument Center (PIC) staff to 

support field operations. The PIC will do its best to provide 

the requested support given the available resources at the 

time of the field campaign. The PIC also reserves the right 

not to provide field support if the field area is deemed to 

dangerous; in such a case the PIC will do all that is possible 

to ensure the success of the experiment. The PIC strongly 

recommends that all PIs take advantage of this resource 

recognizing the expertise that the PIC staff offers field 

operations. Any individual PIC staff will not be required to 

spend more than four (4) weeks supporting a field campaign 

unless special circumstances exist and all parties, PI, PIC 

management and PIC field personnel, have agreed. For field 

campaigns that last longer than four (4) weeks PIs can opt 

to have rotating shifts of PIC staff support. Arrangements 

should be made such that PIC staff arrive in-country after 

the equipment has cleared customs. PIC personnel travel 

arrangements are the responsibility of PASSCAL staff and 

will be coordinated with the PI for both schedule and 

budget considerations. 

PIC Staff and PI Relations 

PIC staff is ‘in the field’ at the request and invitation of the 

PI. As such, PIC staff is there to provide technical support 

and advice to the PI and will defer to the PI regarding 

decisions that impact the experiment. PIC staff will also 

abide by guidelines established by the PI for doing fieldwork 

and respect cultural, religious, and social mores of 

the host country. 

General (applies to all types of experiments) 

On arriving in country, PIC staff is responsible for checking 

the shipment inventory, setting up the field lab, and providing 

all in-country software and hardware training. PIC staff 

is responsible for determining that all PASSCAL equipment 

is functioning prior to deployment. Any equipment damaged 

in shipping will be repaired to the best of PIC staff 

ability. The equipment will be tested during a huddle test 

at which time complete stations will be assembled in a lab 

environment and the PI approved recording parameters will 

be tested. If time permits and the above responsibilities have 

been satisfied, PIC staff can participate in the deployment 

of seismic stations or any other tasks identified by the PI 

that will aid in the success of the experiment. Under no 

circumstances will PIC staff take personal time during an 

experiment unless granted by the PI. 

Active Source 

For active source experiments PIC staff is responsible for 

ensuring that all of the instruments have been correctly 

programmed prior to deployment. After the recording, PIC 

staff is responsible for offloading all of the data, performing 

QC, creating backups of the raw data, and reprogramming 

the instruments if necessary. If time permits, PIC staff can 

produce record sections at the PI’s request. 

Passive Recording 

For broadband passive experiments an overnight huddle 

test will be performed to allow for the sensors to stabilize. 

PIC staff should participate in at least the first several 

installations to provide expert advice and help finalize 

the station design. 

61

Appendix G 

Policy for an IRIS Rapid Array 

Mobilization Program (RAMP) 

Introduction: What is RAMP? 

RAMP is a component of the IRIS response to unanticipated 

seismic events such as earthquakes or volcanic eruptions. It 

permits deployment of instruments in the field on a timetable 

that is not possible within the conventional PASSCAL 

structure. It is justified on the basis of the potential scientific 

return from studies of aftershocks of a significant earthquake 

or of other seismic sources, and represents a natural and 

responsible effort by the seismological community to address 

a societal need. 

IRIS Policy and Resources 

The initiative for a RAMP must come from the scientific 

community. The decision on whether IRIS will support a 

RAMP is ultimately the decision of the IRIS president and 

will generally be made within 24 hours of a request for 

RAMP instruments. The decision will be based on the guidelines 

outlined in Appendix A. IRIS will provide the following 

services to scientists undertaking a RAMP. 

• Large scale effort (>$100K) for an exceptional event 

such as Loma Prieta. 

• Modest support ($10-30K) to support small arrays 

deployed for relatively short times. 

• Loan of instruments only. 

These levels of support include, at most, funds for data 

acquisition and processing to generate a data base suitable 

for submission to the DMC in a timely manner. Funds 

for scientific analysis of the data or for instrument loan 

on a long-term basis must be arranged separately. Given 

expected rates of seismicity and funding limitations, level 

2 efforts might be supported 2-4 times/year, whereas level 

1 efforts might be supported once every 2-5 years. Of 

course, there may be exceptions to these estimates, given 

the unpredictability of Mother Nature. 

C. IRIS will be responsible for coordinating RAMP activities 

with other agencies such as NSF, USGS, NCEER, EERI, 

UNAVCO, SCEC, FEMA, CDMG. Policies pertaining to 

detailed coordination will be developed in conjunction 

with these agencies. 

A. IRIS has dedicated 10 6-component REF TEKs to this 

program at the present. RAMP instruments are expected 

to be at the instrument center when not in the field for a 

RAMP deployment, and are not considered as part of the 

general PASSCAL instrument pool during the normal 

PASSCAL scheduling process. 

D. IRIS maintains the right to recall instruments lent 

either through RAMP or through the normal PASSCAL 

program in the case of an instrument shortage due to an 

important event occurring on the heels of another. IRIS 

hopes that the instrument pool will be large enough for 

this to rarely be necessary. 

B. The level of IRIS support for a RAMP response will fall 

within one of three possible categories, depending on the 

significance of the event and the scientific potential of the 

opportunity. 

E. Additional resources provided by IRIS: 

1. Training interested scientists on use of instrumentation. 

IRIS expects that PI’s proposing a RAMP will 

have already undergone training and does not intend 

to routinely provide technical field support for 

RAMPS activities. 

62

2. Maintaining current lists of trained instrument users 

and compatible instrumentation that might be available 

within the IRIS community . 

3. Facilitating organization of regional planning groups 

(see III.A.). 

4. Acting as an scientific information center during a 

RAMP response. 

5. Developing and distributing software at the DMC for 

rapid processing of data from a RAMP. 

Obligations of RAMP 

Participants 

A. Initiation of a RAMP will generally be in response to a 

request from the scientific community. IRIS expects that 

individual groups interested in conducting a RAMP for 

a given event will communicate among themselves and 

develop a deployment plan before contacting IRIS. To 

facilitate this process IRIS will conduct workshops to 

organize regional interest groups and plan responses. 

B. Participants are responsible for obtaining training on 

PASSCAL instruments prior to deployment. 

C. Participants are responsible for obtaining necessary permission 

and/or official permits for deploying instruments. 

D. Data collected during a RAMP must be submitted to the 

DMC within 6 months of the deployment. This deadline 

is shorter than that for a normal PASSCAL program (ie. 

1 year) because of the timely nature of the data collected. 

Appendix A: 

Guidelines and Procedures 

Criteria for Supporting a RAMP 

Level 1: A very important event because of magnitude, 

location, and/or social impact. (examples: Loma Prieta, New 

Madrid [1811]) 

Level 2: An important event with broad-based scientific 

interest (examples: Joshua Tree, Mendocino Triple Junction, 

Borah Peak) 

Level 3: Events of significant scientific interest when other 

instruments are not available (examples: large man-made 

shots of opportunity, moderate-size regional earthquakes of 

significant scientific interest) 

(note: Requests for instruments to support RAMPs outside 

of the US must also demonstrate advance preparation to 

assure customs clearance for the equipment and adequate 

access to deployment sites.) 

How to Activate a RAMP 

Call or send email to: 

Jim Fowler 

(505) 835-5072 

jim@iris.edu 

or 

David Simpson 

(202) 682-2220 

simpson@iris.edu 

63


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