High resolution imaging of the San Andreas Fault System in Baja California, Mexico using triple-difference tomography

Raul R. Castro, Pieter-Ewald Share, Antonio Vidal-Villegas, Luis Mendoza, & Yehuda Ben-Zion

Submitted August 14, 2019, SCEC Contribution #9603, 2019 SCEC Annual Meeting Poster #138

Understanding transform plate boundary processes and the associated seismic hazard for society requires knowledge of the geometry and material properties along major faults comprising these boundaries. High-resolution properties of the San Andreas Fault System (SAFS) in Southern California have been obtained through various studies, but corresponding information for the SAFS in northern Baja California is less clear. Deriving high-resolution velocity models of the SAFS that continuously extend from Southern to Baja California is important for understanding the plate boundary. Toward this goal, we image the seismogenic crust in the area at high-resolution using arrival time tomography that incorporates both station-pair and event-pair double differences (triple-difference tomography). The study uses arrival time data of local earthquakes and stations from the Seismological Network of CICESE (Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California, México) and the Southern California Seismic Network. In total, ~1,400,000 P-wave and ~1,300,000 S-wave arrival times associated with more than 200 stations and more than 18,000 events (from 2003-2018) are used in the tomographic inversion. Preliminary results show that regionally the mid to upper crust encompassing the San Jacinto, Elsinore and Laguna Salada fault zones has very low P-wave velocities, and average to low S-wave velocities owing to the presence of large volumes of felsic rocks within the eastern Peninsular Ranges Batholith. At depths greater than 7 km, northeast of the Laguna Salada fault and near the rupture area of the El Mayor-Cucapah earthquake, there is a sharp change from these low velocities to high P-wave and S-wave velocities in the northeast, suggesting the presence of a bimaterial structure in the core of the El Mayor-Cucapah source region and the general plate boundary in the area. The most pronounced low S-wave anomaly at depths greater than 11 km extends from the southern end of the Elsinore fault to the El Mayor-Cucapah source region, indicating an area of extensively damaged and deformed rocks. Other major mapped fault zones in northern Baja California also have anomalously low velocities, for instance along the Sierra Juarez fault. These and further updated results will be presented at the meeting.

Key Words
Imaging San Andreas fault, Baja California, tomography

Citation
Castro, R. R., Share, P., Vidal-Villegas, A., Mendoza, L., & Ben-Zion, Y. (2019, 08). High resolution imaging of the San Andreas Fault System in Baja California, Mexico using triple-difference tomography. Poster Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
San Andreas Fault System (SAFS)