Inter-event, Kinematic and Post-seismic slips of the 2019 RidgeCrest earthquakes: insights into the seismic/aseismic slip behaviors

Abstract:

Cascade and slow-slip processes are commonly believed to control interactions between foreshocks, mainshocks and aftershocks, although their relative contributions remain poorly resolved. Discrimination between these processes will shed light on the understanding of earthquake physics, although this requires exceptional observations of earthquake sequences. The well-recorded 2019 Ridgecrest, California earthquake foreshock-mainshock sequence provides such an opportunity. A comprehensive study of seismic and geodetic data reveals the co-seismic and inter-event (between the foreshock and mainshock) slip processes of this sequence. The overall sequence involved no less than 4 fault planes with sub-parallel or orthogonal geometry.

We developed a linear inversion algorithm fully utilizing the timeseries of daily-GPS, SAR image sequences and strainmeters to exploit quasi-static slips on the fault plane. We use plane strain tensors timeseries recorded by two nearfield strain meter stations to recover the inter-event slip distribution between the fore- and mainshocks. We resolve distinct seismic (cascade) and aseismic (slow-slip) offsets on the primary orthogonal faults ruptured in the foreshock during the inter-event period, and find that asperity sizes and/or co-seismic stress changes, along with the unusual orthogonal fault geometry may have contributed to this dual-mode slip behavior. We also utilize GPS and SAR timeseries of the post-seisminc period to recover the after-slips of the mainshock. Main afterslips are recovered on two rupture ends of the main fault plane. For the othogonal fault, slow-slips are concentrated near its junction with the main fault plane and migrate to the outer-side. Such migration is consistent with the after-shock migration, which appears to be controlled by the mainshock stress changes.