Stress analysis and rupture dynamics of the 2019 Ridgecrest Earthquake sequence

Abstract:

Stress transfer from long-term loading as well as prior earthquakes can initiate seismic triggering and strongly affect rupture propagation (RP) and slip patterns (SP) in a fault system. A prime example of this effect is the 2019 Ridgecrest earthquake sequence, which consists of multiple complex conjugate fault ruptures with delayed rupture triggering. On July 4th, 2019 a M6.4 earthquake took place in California, resulting in left lateral surface ruptures as well as slip on a buried right-lateral conjugate fault. Approximately 30 hours later an M5.4 earthquake ruptured ~10km northwest of the M6.4 hypocenter, then 6 hours later an M7.1 main shock occurred almost 2 km west of the M5.4 event. Although these three events are almost certainly related, the temporal separation between them would seem to argue against the role of pure dynamic triggering. However, longer term triggering can be explored through the investigation of stress transfer caused by the fault systems response to RP and SPs. In this study, we utilize 3D finite element dynamic rupture models to explore RP’s influence on seismic triggering on a system with complex fault geometry, including all three major events in this rupture sequence. Dynamic rupture models are extremely sensitive to the fault geometry, so our model is constrained by both observed surface ruptures and aftershock data. Preliminary results of our M6.4 dynamic models suggest that the residual stress field from this event had a strong effect on the fault that would subsequently host the M7.1 event. Our study illustrates that RP from one fault to another is strongly dependent on the level of overall stress as well as the details of fault geometry, including depth of fault burial. Further extrapolation to a more realistic fault structure will include fault complexity that results from fitting the complex surface rupture to the simpler seismicity patterns at depth. We will explore how the implementation of this fault geometry changes the seismic response of the system (including the stress interactions between the faults) relative to simpler implementations of fault geometry. Investigating the physical mechanisms associated with this seismic domino effect will improve our knowledge regarding fault interactions.