Effects of Near‐Fault Sedimentary Rocks and Damage on the 2019 Ridgecrest, CA Earthquake: A Rupture Impediment or a Ground Motion Booster?

Abstract Observations of the 2019 magnitude 7.1 Ridgecrest, California, earthquake indicate a relatively slow rupture (2 km/s). The fault is surrounded by sedimentary rocks and low‐velocity damage zones, which can amplify ground motions but also slow down rupture. Here, we develop 3D dynamic rupture models to elucidate the significance of such effects on the Ridgecrest earthquake. We find that: (a) sedimentary rocks and damage, being shallow, do not explain the slow rupture but amplify slip and ground motion by more than a factor of 3; (b) accounting for ground motion amplification by sedimentary rocks improves the agreement with empirical predictions; (c) damage zone contributions to surface slip are minor (5%) for this event but could reach 25% in future southern California earthquakes. Our study corroborates the significance of source and site effects due to heterogeneous near‐fault materials during the Ridgecrest earthquake, and provides insights for future rupture and source‐to‐site hazard modeling efforts.