Kinematic and Dynamic Inversion to the Afterslip of 2019 Ridgecrest Earthquake Using Geodetic Data

Abstract:

Aseismic afterslip generally occurs on faults following large earthquakes. As a dominant mechanism to release coseismic stresses, afterslips are quite important for understanding frictional behaviors of fault zones. Afterslip on faults is commonly considered to be governed by rate-and-state friction law, in which slip rate is correlated to frictional property (a-b) directly in steady state. Benefiting from the rapid development of geodetic techniques including GPS and InSAR and frequent continental earthquakes, we gained rich post-seismic deformation observations for afterslips. Considering different features of different types of geodetic data (GPS data has high temporal resolution while InSAR data has high spatial resolution), we developed a kinematic and dynamic inversion method to make full use of full timeseries and obtain the distribution of frictional property (a-b) on the fault. We adopted a Bayesian stochastic inversion method utilizing the Markov Chain Monte Carlo (MCMC) sampling algorithm to estimate the probability distribution of inversion parameters. The algorithm is applied to the 2019 Ridgecrest earthquake sequence. We obtained strainmeter data in the inter-event period and GPS+SAR data in the postseismic period and use them in the inversion for spatial distribution of (a-b) in the two periods respectively. Factors controlling the time-evolution of afterslip are also analyzed in our research. The results indicate that the frictional property on the orthogonal fault locates into a conditionally stable-sliding regime. In postseismic period, the faults are dominated by aseismic slow slip, while displacements caused by earthquakes only contribute a small proportion to the total moment release. After the mainshock, the main afterslip area migrates to the outer part of the faults, which can be related to the projection of coseismic stress change on the orthogonal fault system.