HR: 1340h
AN: S13B-1045    [Abstracts]
TI: Preliminary Results of Seismic Refraction/Reflection Experiment in Northwestern Nevada and Northeastern California
AU: * Colgan, J P
EM: jcolgan@geo.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 United States
AU: Lerch, D L
EM: lerch@geo.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 United States
AU: Gashawbeza, E M
EM: ewenet1@geo.stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305-2215 United States
AU: Wilson, C K
EM: wilsonck@geo.stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305-2215 United States
AU: Klemperer, S L
EM: sklemp@stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 United States
AU: Klemperer, S L
EM: sklemp@stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305-2215 United States
AU: Miller, E L
EM: miller@geo.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 United States
AB: In September 2004, Stanford University is conducting a 260-km seismic refraction/reflection experiment across the northwestern margin of the Basin and Range Province between Winnemucca, Nevada and Alturas, California. This area was the locus of intense mid-Miocene (c. 17-15 Ma) volcanism and subsequent high-angle extensional faulting, and is often thought to be the breakout region of the Yellowstone hotspot. Today the region is characterized by high heat flow and is presumed to have relatively thin crust (c. 25 km), but little is known about the overall structure of the crust and how it relates to magmatism and extensional faulting. Our seismic experiment is designed to collect information on the crustal thickness, velocity structure, and crustal-scale reflectivity of this area, and consists of four parts: 1) A 260-km crustal refraction profile, with five in-line shots (1.25 to 2 tons each) and one 1.25 ton fan shot to the south, with over 1000 receivers spaced 100 to 300 m apart, acquired with ACS/PRF and NSF/EarthScope funding. The goals of the refraction profile are to determine crustal thickness and overall velocity and reflectivity structure. 2) While geophones are deployed along the refraction profile, we will collect reflection data in P, SV and SH modes using the tri-axial "T-Rex" vibrator truck operated by the Network for Earthquake Engineering Seismology (NEES) and the University of Texas at Austin. This experiment will asses the capability of this instrument to collect useful crustal-scale reflection data in conjunction with PASSCAL and EarthScope recorders, and if successful will help constrain the types of rocks and structures present beneath the flat-lying Miocene volcanic rocks that cover much of northwestern Nevada and largely obscure older structures. 3) 48 short-period 3-component receivers will be embedded in the main refraction line, supplemented by two 16-receiver offline deployments perpendicular to the main line. This experiment is designed to measure crustal S-wave splitting (PmS phase) from the active source experiment as an indicator of crustal anisotropy resulting from lower crustal flow. We may also detect differences in direct-S travel times using the SV and SH modes of the T-Rex vibrator from the same vibration location. 4) A 16-km high-resolution (40 m receiver spacing) reflection profile across Surprise Valley, CA. This experiment will test the capabilities of the T-Rex vibrator for shallow, high-resolution P and S-wave imaging in a low-cost experiment, and should yield geologically useful information on the depth of basin fill in Surprise Valley above the recently active Surprise Valley fault. We present preliminary data from our experiment and discuss their implications both for regional tectonics, and as a potential model for future EarthScope/NEES collaborations.
DE: 9350 North America
DE: 8109 Continental tectonics--extensional (0905)
DE: 7205 Continental crust (1242)
DE: 0935 Seismic methods (3025)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting