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Major southern San Andreas earthquakes modulated by lake-filling events

Ryley G. Hill, Matthew Weingarten, Thomas K. Rockwell, & Yuri Fialko

Published June 7, 2023, SCEC Contribution #12739

Hydrologic loads can stimulate seismicity in the Earth’s crust. However, evidence for the triggering of large earthquakes remains elusive. The southern San Andreas Fault (SSAF) in Southern California lies next to the Salton Sea, a remnant of ancient Lake Cahuilla that periodically filled and desiccated over the past millennium. Here we use new geologic and palaeoseismic data to demonstrate that the past six major earthquakes on the SSAF probably occurred during highstands of Lake Cahuilla. To investigate possible causal relationships, we computed time-dependent Coulomb stress changes due to variations in the lake level. Using a fully coupled model of a poroelastic crust overlying a viscoelastic mantle, we find that hydrologic loads increased Coulomb stress on the SSAF by several hundred kilopascals and fault-stressing rates by more than a factor of 2, which is probably sufficient for earthquake triggering. The destabilizing effects of lake inundation are enhanced by a nonvertical fault dip, the presence of a fault damage zone, and lateral pore-pressure diffusion. Our model may be applicable to other regions in which hydrologic loading, either natural or anthropogenic, was associated with substantial seismicity.

Hill, R. G., Weingarten, M., Rockwell, T. K., & Fialko, Y. (2023). Major southern San Andreas earthquakes modulated by lake-filling events. Nature, 1-6. doi: 10.1038/s41586-023-06058-9. https://www.nature.com/articles/s41586-023-06058-9