How 1000 years of earthquakes have shaped the stress distribution in the Eastern California Shear Zone: seismic hazards before and after the 2019 Ridgecrest earthquake sequence

The 2019 Ridgecrest earthquake sequence took place on strike-slip faults in an area where recent studies on cumulative (coseismic plus postseismic) Coulomb stress change (ΔCFS) indicate an increase in stress on faults with this kinematics. The occurrence of these earthquakes thus supports the hypothesis that the spatial and temporal distribution of major earthquakes in this region is controlled to a significant extent by the location and timing of past events. The stress changes produced by the 2019 earthquakes should then tell us which other faults in the Eastern California Shear Zone (ECSZ) may have been brought closer to failure.

In order to identify such faults, we model the stress history in the ECSZ by calculating the cumulative ΔCFS due to several M ≥ 7 earthquakes that occurred in the ECSZ and surrounding region in the last ~1000 years, up to and including the 2019 Ridgecrest earthquake sequence. We focus specifically on the southern Sierra Nevada fault zone, Garlock fault, and Blackwater fault, but also consider stress changes to the southern part of the Owens Valley fault, and to several other normal faults in the area. We also determine the effect of the calculated ΔCFS on the time-dependent probability of occurrence of major earthquakes in the ECSZ, with particular focus on the Garlock fault.