Postseismic deformation and stress evolution following the 2019 M 7.1 and M 6.4 Ridgecrest earthquakes

Jacob H. Dorsett, Kaj M. Johnson, Simone Puel, & Thorsten W. Becker

Published August 15, 2019, SCEC Contribution #9789, 2019 SCEC Annual Meeting Poster #236

The 2019 M 7.1 and M 6.4 Ridgecrest earthquakes present the first opportunity to study ongoing postseismic deformation and crustal stress evolution following a large earthquake in southern California in two decades. Coseismic Coulomb stress changes are widely used to investigate potential loading of nearby faults. However, at greater distances from the rupture, postseismic stress changes driven primarily by viscous mantle flow can exceed the magnitude of coseismic stress changes. To investigate this stress evolution, we generate viscoelastic Green’s functions for the Ridgecrest sequence using the finite element code PyLith to compute time-dependent surface deformation and stress changes. We then use these in conjunction with a range of fault constitutive laws and a suite of coseismic slip models to compute the postseismic deformation due to afterslip and coupled mantle flow as well as a range of expected postseismic Coulomb stress changes. Preliminary models utilize an elastic crust overlying a mantle with uniform viscosity and make comparisons to rapid GPS solutions, while our more sophisticated models will incorporate both a 3D viscosity model and observations from InSAR. Preliminary model results broadly approximate the observed surficial patterns of displacement 20 days after the rupture using a mantle viscosity of order 1017-1018 Pa s. After 20 days, postseismic stress changes begin to exceed the magnitude of coseismic stress changes at distances greater than 50 km from the hypocenter, often with a sign opposite to coseismic changes. From these preliminary results, it is apparent that the postseismic fault loading from the Ridgecrest sequence may represent a significant portion of total stress redistribution, and that patterns can be inconsistent with coseismic loading. This postseismic effect may contribute to aftershocks in the weeks after a large rupture and would have to be included in any time-dependent hazard assessment. We hope to streamline this near real-time technique for use in future aftershock forecasting.

Citation
Dorsett, J. H., Johnson, K. M., Puel, S., & Becker, T. W. (2019, 08). Postseismic deformation and stress evolution following the 2019 M 7.1 and M 6.4 Ridgecrest earthquakes. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes