SEMINAR - Daniel Brothers

Imaging the fault structure and earthquake history beneath the Salton Sea

Daniel S. Brothers
Scripps Institution of Oceanography
Institute of Geophysics and Planetary Physics
University of California, San Diego

April 30th, 2008

The Salton Sea, California, covers an important section of the plate boundary where the Gulf of California ridge-transform system to the south transitions into the San Andreas strike-slip system to the north. However, this transition zone is poorly understood due to an absence of detailed geological and geophysical data beneath the Sea. To constrain deformation models and seismic hazards in this region we need to define the location, kinematics and rupture history of faults beneath the Sea and determine how these structures affect stress conditions along major faults in the region, such as the San Andreas and San Jacinto.

High-resolution seismic reflection data collected in 2006 and 2007 provide the first regional-scale imagery of faulting and stratigraphy beneath the Salton Sea. Seismic profiles reveal structural features that were previously unknown, including the continuation of the Extra Fault Zone (EFZ) between the San Felipe Hills and Durmid Hill, as well as several faults and seafloor scarps in the Brawley Seismic Zone. By correlating acoustic marker beds in the seismic data with stratigraphy documented in paleoseismic trenches onshore, we are able to constrain both the depositional history and the timing of past earthquakes beneath the Sea.