2004 AGU Fall Meeting

A Pilot Experiment in Collaborative Science and Engineering

AU: * Steidl, J H
EM: steidl@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California at Santa
Barbara, Santa Barbara, CA 93106 United States

AU: Working Group, G
EM: gomberg@usgs.gov
AF: Institute for Crustal Studies, University of California at Santa
Barbara, Santa Barbara, CA 93106 United States

AB: We report on a pilot field experiment, meant to demonstrate the
value of combining resources from multiple earthquake science and
engineering facilities. Our initial intent was to employ a mobile shaker
truck from the Network for Earthquake Engineering Simulation (NEES)
facility with US Geological Survey (USGS) and Incorporated Research
Institutions for Seismology (IRIS) seismographic instrumentation in a
single study. The final experiment grew into four studies with additional
participation from the Los Alamos National Lab and other NSFsponsored
consortia; the MAEC, SCEC, CENS, and HPWREN. The field
experiment piggybacked on an earlier planned inaugural demonstration
of NEES facilities, held at the NEES Garner Valley Digital Array (GVDA)
site in southern California. We recorded ground motions generated by
the `TRex' shaker truck at the GVDA and surrounding Garner Valley
during August 18-22, 2004 and will continue to collect earthquake data
for several months. Our first study tests the potential for generating
and measuring nonlinear sediment response by recording TRex strong
shaking on a temporary surface accelerometer micro-array and
permanent GVDA down-hole accelerometers. Our second study focuses
on ground motion site and basin effects by recording TRex signals at 20
temporary real-time, telemetered seismic stations deployed from the
center to the edge of the basin. Earthquake signals recorded on this
basin array will allow us to validate the process of extrapolating results
from the artificial, surface source to those from natural earthquakes.
The relatively small scale of the Garner Valley basin (4 km by 10 km,
sediment depths less than 25 m) makes its characterization feasible, but
scalable to larger basins elsewhere and motivates our third study in
which we conduct a variety of imaging experiments. Basin array data
will constrain broad-scale shear and compressional wave tomographic
images of the basin structure. To constrain a higher-resolution image
along a profile across the basin, we also collected reflection data
generated by TRex recorded on densely spaced geophone strings, and
conducted a sledge-hammer survey at even higher resolution to confirm
the location of a suspected buried fault. For the fourth study, we assess
the potential for shakers like TRex to do broad-scale, deep imaging as
we stack TRex signals emitted repeatedly for nearly an hour, recorded
on stations of the regional ANZA and statewide California Integrated
Seismic Networks.