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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-
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