Direct Evidence For Linked San Jacinto-san Andreas Earthquakes

Alba M. Rodriguez Padilla, Michael E. Oskin, Thomas K. Rockwell, Irina Delusina, & Drake M. Singleton

Submitted February 18, 2021, SCEC Contribution #10924

Large, multi-fault earthquakes increase the threat of strong ground-shaking and modify the probability of moderate events, hindering the use of long-term seismic-hazard models. Understanding the physics and recurrence of multi-fault events is challenged by the lack of information in the gaps between co-rupturing faults. We directly document the co-rupture history of the San Andreas and the San Jacinto faults, two major plate-boundary strike-slip faults that approach within 3.5 km near Cajon Pass, 70 km east of Los Angeles, California. Paleoseismic trenching of the Lytle Creek Ridge Fault (LCRF), a low angle normal fault uniquely positioned and mechanically favored to record ruptures that bridge the gap, shows that joint ruptures occurred at least three times in the past 2500 years, most recently in the historic 1812 event.

Rodriguez Padilla, A. M., Oskin, M. E., Rockwell, T. K., Delusina, I., & Singleton, D. M. (2021). Direct Evidence For Linked San Jacinto-san Andreas Earthquakes. Science, (submitted).