HR: 0804h
AN: NS11E-0839    [Abstracts]
TI: Combined Seismic Reflection and Refraction Profile Across the Hayward Fault in Fremont, Alameda County, California
AU: * Goldman, M R
EM: goldman@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, MS 977, Menlo Park, CA 94025, United States
AU: Catchings, R D
EM: catching@usg.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, MS 977, Menlo Park, CA 94025, United States
AU: Rymer, M J
EM: mrymer@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, MS 977, Menlo Park, CA 94025, United States
AB: In late July of 2007, we acquired a ~300-m-long combined seismic reflection and refraction profile across the Hayward fault in Fremont, California. The profile was located in order to image an inferred structural stepover of the main trace of the fault. We used fifty-eight 40 Hz P-wave geophones in a linear array with a spacing of 5 m. Seismic sources consisted of repeated sledgehammer strikes at each geophone location. The P-wave geophones were then replaced by 4.5 Hz S-wave geophones, orientated perpendicular to the profile. Sledgehammer strikes were then repeated at each location using a custom-built S-wave generator consisting of a large aluminum block, which was struck at both ends; cleats on the bottom of the block helped couple the block to the ground. All shots were recorded by all of the geophones, allowing for both refraction and reflection processing. We created a tomographic velocity image from the P-wave data in order to image the structure of the Hayward fault at this location, and to stack the seismic reflection data. We also created a tomographic velocity image from the S-wave data in order to calculate Poisson's ratio and a Vp/Vs ratio along the profile. All of these data contribute to defining fault location, geometry, and structure.
DE: 7270 Tomography (6982, 8180)
DE: 7299 General or miscellaneous
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting