PRELIMINARY RESULTS FROM THE 2004 STANFORD UNIVERSITY SEISMIC EXPERIMENT: A 260 KM REFRACTION/REFLECTION/TELESEISMIC EXPERIMENT IN THE NORTHWESTERN BASIN AND RANGE

Results from various aspects of the 2004 Stanford University seismic experiment across the northwestern Basin and Range transition zone will be presented. This survey, a 260 km seismic refraction/reflection/teleseismic experiment, offers new constraints regarding the crustal structure of this relatively unstudied corner of the Basin and Range Province. This region was the locus of intense mid-Miocene (ca. 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 relatively thin crust (28-30 km), with little known about the overall structure of the crust and how it relates to magmatism and extensional faulting. Our seismic experiment collected information on the crustal thickness, velocity structure, anisotropy, and reflectivity of this area, and consisted of 4 parts: (1) A 260 km crustal refraction profile, with 5 in-line shots, one fan shot to the south, and three nearby mine-blasts, with ~1100 receivers spaced 100-300 m apart, determining crustal thickness and overall velocity structure. (2) During the deployment for the refraction experiment, we collected reflection data from both P and S-wave sweeps with the tri-axial “T-Rex” vibrator truck operated by the Network for Earthquake Engineering Seismology (NEES) and the University of Texas at Austin to assess the capability of this vibrator to collect useful crustal-scale reflection data. (3) Forty-eight short-period 3-component receivers were embedded in the main refraction line, supplemented by two 16-receiver offline deployments perpendicular to the main line, 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. (4) A 20 km high-resolution (40 m receiver spacing, 10 m source spacing) reflection profile across Surprise Valley, CA, probing the depth and velocity structure of the basin fill beneath the seismically and geothermally active Surprise Valley. Here, we present preliminary data from this experiment and discuss their implications for regional tectonics.