Stress Changes on the Garlock Fault during and after the 2019 Ridgecrest Earthquake Sequence

Abstract

ABSTRACTThe recent 2019 Ridgecrest earthquake sequence in southern California jostled the seismological community by revealing a complex and cascading foreshock series that culminated in a Mw 7.1 mainshock. But the central Garlock fault, despite being located immediately south of this sequence, did not coseismically fail. Instead, the Garlock fault underwent postseismic creep and exhibited a sizeable earthquake swarm. The dynamic details of the rupture process during the mainshock are largely unknown, as is the amount of stress needed to bring the Garlock fault to failure. We present an integrated view of how stresses changed on the Garlock fault during and after the mainshock using a combination of tools including kinematic slip inversion, Coulomb stress change (ΔCFS), and dynamic rupture modeling. We show that positive ΔCFSs cannot easily explain observed aftershock patterns on the Garlock fault but are consistent with where creep was documented on the central Garlock fault section. Our dynamic model is able to reproduce the main slip asperities and kinematically estimated rupture speeds (≤2 km/s) during the mainshock, and suggests the temporal changes in normal and shear stress on the Garlock fault were the greatest near the end of rupture. The largest static and dynamic stress changes on the Garlock fault we observe from our models coincide with the creeping region, suggesting that positive stress perturbations could have caused this during or after the mainshock rupture. This analysis of near-field stress-change evolution gives insight into how the Ridgecrest sequence influenced the local stress field of the northernmost eastern California shear zone.