The role of crustal mechanics and frictional heterogeneity in post-seismic deformation of the 2019 Ridgecrest earthquake

Yohai Magen, Alice-Agnes Gabriel, Dave A. May, & Piyush Karki

Submitted September 7, 2025, SCEC Contribution #14736, 2025 SCEC Annual Meeting Poster #TBD

The 2019 Ridgecrest earthquake sequence ruptured a complex network of orthogonal faults in eastern California, and included a Mw7.1 mainshock. To the north, the mainshock rupture stopped at Coso, an active volcanic region with increased heat flow and shallower ductile-to-brittle transition zone. Both aftershock evolution and Burst Overlap Interferometry (BOI) geodetic observations of post-seismic deformation exhibit a higher temporal decay rate in the vicinity of COSO compared to across the main section of the Mw7.1 earthquake. BOI retrieves the deformation field from the SAR satellite track, which is more than 4 times sensitive to displacement parallel to the Mw7.1 main fault strike over commonly used interferograms, which view the deformation field in the line of sight of the satellite. In addition to the change in temporal behavior, the BOI data reveals 4 cm of displacement in the along-track direction in the vicinity of Coso, and only 3 cm across the co-seismically active faults where we expect to find the maximum post-seismic deformation. These observations highlight the importance of better understanding the effects of variable crustal properties on the mechanics after and during large earthquakes.
Here, we present a physics-based rate-and-state-friction after-slip model self-consistently explaining those observations. We utilize the open-source seismic cycle and aseismic slip (SEAS) simulation framework Tandem. This modeling framework utilizes a discontinuous Galerkin (DG) finite element method and high-performance computing (HPC). As initial condition, we use the parameters sampled from a dynamic rupture model of the earthquake's coseismic phase (Taufiqurrahman et al., 2023) to initiate the post-seismic response. To capture the observed seismicity and deformation change rate as a function of the distance to Coso, we vary the difference between the direct effect parameter (a) and the evolution effect parameter (b) of the velocity-strengthening portion of the fault. We find that an increase in the difference(a-b) from 0.01 along the main section of the fault to 0.025 near Coso can explain the change in temporal behavior. We will discuss the tradeoff between modeling these observations as an after-slip event versus a viscoelastic response of the crust. We will also outline next steps to implement fully coupled rate-and-state friction and viscoelasticity within Tandem.

Citation
Magen, Y., Gabriel, A., May, D. A., & Karki, P. (2025, 09). The role of crustal mechanics and frictional heterogeneity in post-seismic deformation of the 2019 Ridgecrest earthquake. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)