Complex postseismic relaxation following the 2019 Ridgecrest earthquake sequence illuminated by high-resolution geodetic observations

Kang Wang, Roland Bürgmann, Liu Zhen, Eric J. Fielding, Benjamin A. Brooks, & Jerry Svarc

Published 2022, SCEC Contribution #12707

Postseismic deformation following large earthquakes carries rich information about the rheological properties of faults and surrounding rocks. In this study we characterize the spatial and temporal distribution of postseismic deformation ~2.5 years after the 2019 Ridgecrest earthquake sequence with high-resolution geodetic measurements of InSAR and GNSS. We show that all three commonly considered postseismic relaxation mechanisms, including afterslip, poroelastic rebound and viscoelastic rebound, are required to explain the postseismic deformation observed by InSAR and GNSS ~2.5 years after the mainshock. Specifically, the near-to-medium field postseismic GNSS and InSAR displacements are dominated by afterslip and poroelastic rebound, while the far-field GNSS data are best explained by viscoelastic relaxation in the upper mantle. Similar to the coseismic rupture, the distribution of afterslip is relatively shallow (>15 km), with the most prominent slip being found mainly around the areas of high coseismic slip. The inferred afterslip model can well explain the horizontal components of the InSAR and GNSS observations, but it predicts opposite signs of vertical motion seen in places that involve fault geometry complexities, including the area around the mainshock epicenter, where the strike varies to form a releasing bend, the fault junction between the fore- and mainshock ruptures, as well as the areas around mainshock rupture tips. Assuming that the near-field vertical postseismic deformation is mainly due to poroelastic rebound, we explore the hydrological properties of the shallow crust, particularly the hydraulic diffusivity, which controls the speed of pore-pressure diffusion and the corresponding surface deformation. We show that the Sentinel-1 LOS displacement time series from the ascending track 64 and GNSS time series at sites close to the mainshock epicenter are consistent with poroelastic rebound models with a hydrological diffusivity of ~0.1 m^2/s in the top 2km.

Citation
Wang, K., Bürgmann, R., Zhen, L., Fielding, E. J., Brooks, B. A., & Svarc, J. (2022). Complex postseismic relaxation following the 2019 Ridgecrest earthquake sequence illuminated by high-resolution geodetic observations. Poster Presentation at NASA Solid Earth Team Meeting.