Geodetic Investigation of Compliant Fault Zones on the San Francisco Peninsula segment of the San Andreas Fault

Abstract:

At many places along the San Andreas Fault, geodetic and seismic studies have suggested the presence of near-field compliant fault zones (CFZs). These zones of damaged rock display reduced elastic moduli compared to intact rock, resulting in both higher geodetic strain rates and lower seismic velocities within the fault zones. In this study, we investigate the CFZ surrounding the San Andreas Fault in the San Francisco Peninsula by examining interseismic deformation over the past several decades. We use new and existing survey GPS measurements, as well as older electronic distance measurements, to characterize the deformation of the CFZ. The data come from networks at Black Mountain and Lake San Andreas, both small-aperture geodetic networks on the San Francisco Peninsula with survey GPS occupations spanning at least 15 years. We compare the inferred fault zone properties between the two networks, which are separated by less than 40 kilometers but which represent different geologic boundaries and show different fault ages. We also compare patterns in seismicity between the two regions. The differences in inferred fault parameters between these two regions may be related to differences in fault age and development, giving clues into how CFZs develop over time.