f NEAR-SURFACE SEISMIC SURVEYING ALONG THE GREEN VALLEY FAULT, SAN FRANCISCO BAY AREA, CALIFORNIA

Seismic reflection surveying was conducted at the Green Valley fault, located in the San Francisco Bay Area, California, with the goal of identifying subsurface stream channels for use in measuring fault offset and slip rate. Three 180-m long, fault-parallel profiles were recorded in 2009 near the site of previous paleoseismologic investigations, including near-surface geophysical surveys. A previous seismic refraction survey identified a trough-shaped, low velocity body on the east side of the fault at depths of 5-12 m, interpreted as a stream channel truncated by the Green Valley fault. The present work was undertaken with the goal of finding the corresponding portion of the channel on the west side of the fault, presumably offset to the north due to motion on the fault during approximately the past 10 ka. Seismic reflection data were recorded in order to obtain higher-resolution and more extensive coverage. The new survey provided excellent resolution of near-surface stratigraphy at depths of 80-375 m, but did not provide sufficient resolution at shallower depths to permit correlation with data from the earlier seismic refraction survey, which had a maximum depth penetration of only about 15 m. The new reflection data appear to image lateral variations in fluvial stratigraphy at depths of approximately 100 m that could be used to measure fault offset in a future study.