Controls of Dynamic and Static Stress Changes and Aseismic Slip on Delayed Earthquake Triggering in Rate-and-State Simulations of the 2019 Ridgecrest Earthquake Sequence

Jeena Yun, Alice-Agnes Gabriel, Dave A. May, & Yuri Fialko

Published September 8, 2024, SCEC Contribution #13949, 2024 SCEC Annual Meeting Poster #148

Earthquake dynamic triggering frequently exhibits a time delay relative to the peak stress perturbation. For example, the 2019 Mw 7.1 Ridgecrest, CA, mainshock occurred 16.2 hours after a nearby Mw 5.4 foreshock, which induced dynamic stress changes of the order of megapascals at the mainshock hypocentral area. In this study, we investigate the physical mechanisms underlying delayed triggering on a fault that is on the verge of a runaway rupture. We first compute detailed spatio-temporal changes in the dynamic and static Coulomb stress at the Ridgecrest mainshock hypocenter caused by the Mw 5.4 foreshock using 3D dynamic rupture models (SeisSol). We then model quasi-dynamic seismic cycles on a 2D strike-slip fault governed by rate-and-state friction using the open-source software Tandem. We incorporate self-affine heterogeneities in the initial stress and frictional properties to produce complex earthquake sequences on the mainshock fault. These cycle models exhibit a broad spectrum of fault slip; system-size earthquakes are always preceded by a cascade of partial ruptures. The cycle models are perturbed using the calculated dynamic and static stress history from the Mw 5.4 foreshock. We generate multiple scenarios with different hypocenter depth, amplitude and timing of perturbation, and evolution laws (aging, slip, and stress-dependent law).
Most of the perturbed cycle models yield a clock advance of several hours. We observe instantaneous triggering only if the peak stress perturbation is on the order of 20 MPa, comparable to the strength glut during quasi-static nucleation. While the aging and slip laws yield similar clock advances, the stress-dependent aging law leads to a systematic decrease in clock advance. The mainshock clock change in the model is dominantly controlled by the interplay of the depth-dependent static stress change and background aseismic slip. The sign of stress perturbation in areas of accelerating slip controls the advance versus delay of the mainshock. In these models, a mainshock can be promoted even when the static stress change does not favor a rupture at the future mainshock hypocenter depth, due to the stress transfer driven by the foreshock sequence. Our results emphasize the importance of foreshock sequences and aseismic deformation as controlling factors of earthquake triggering. Tandem Apps (2D, 3D) are accessible through the QuakeWorx Science Gateway.

Citation
Yun, J., Gabriel, A., May, D. A., & Fialko, Y. (2024, 09). Controls of Dynamic and Static Stress Changes and Aseismic Slip on Delayed Earthquake Triggering in Rate-and-State Simulations of the 2019 Ridgecrest Earthquake Sequence. Poster Presentation at 2024 SCEC Annual Meeting.

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