Southern San Andreas Fault Zone

The San Andreas Fault (SAF) in California is a mature plate boundary fault capable of great (magnitude 8 or greater) earthquakes. The southern section of the SAF has not produced a major event in historic times (over the last 300 years), and is currently believed to pose the largest seismic risk in California (Weldon et al., 2005; Field et al., 2014). While much progress was made toward understanding seismic potential of the Southern San Andreas Fault (SSAF) and the likely socio-economic impacts of a large future earthquake on the SSAF, several important questions remain. Over the last decade several lines of evidence emerged suggesting that the 80 km-long Coachella Valley- Bombay Beach segment of the SSAF may not be vertical and may have a substantial dip to the East, similar to a well-recognized SSAF dip in the San Gorgonio bend further to the North. We propose to test this hypothesis by imaging a low-rigidity damage zone and/or a bi-material interface associated with the SSAF in the upper crust. This will be accomplished by deploying a dense seismic array spanning the SSAF in the Mecca Hills area. Data from the deployed seismic array and regional seismic networks will be used to generate high-resolution tomographic images of the fault zone throughout the seismogenic layer. Seismic data will be combined with high-resolution geodetic observations to place robust constraints on the subsurface geometry and mechanical properties of the bi-material interface and/or damage zone associated with the SSAF.