Observations and models of crustal deformation transients following the 2019 Ridgecrest, California, earthquake sequence

The 2019 Ridgecrest, California, earthquake sequence involved predominantly right-lateral strike slip on a NW-SE trending subvertical fault in the July 5 M7.1 mainshock, preceded by left-lateral strike slip on a NE-SW trending subvertical fault in the July 4 M6.4 foreshock. It produced observable crustal deformation over much of Central and Southern California, as well as surface rupture over several tens of km along both fault trends. To obtain a detailed picture of the fault slip and postseismic processes, we assemble deformation observations including Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), and Mobile Laser Scanning (MLS) data, appended by field observations of surface slip. The geodetic measurements variously illuminate coseismic deformation (e.g., kinematic solutions from continuous GPS; MLS), combined coseismic and postseismic deformation (InSAR), or just postseismic deformation following the mainshock (GPS; MLS; InSAR). The postseismic deformation is particularly well constrained from survey-mode GPS in the epicentral region carried out during the weeks after the mainshock. In parallel work (J.R. Murray et al., presented at this meeting), geodetic data is used to infer coseismic slip models of these earthquakes. Using coseismic slip models, we will interpret observations of postseismic deformation with mechanical models including both afterslip and viscoelastic relaxation of the lower crust and mantle asthenosphere. InSAR measurements of line-of-sight displacement during the first three postseismic weeks yield ~10 mm postseismic motion across the southern portion of the mainshock rupture within a ~2 km wide zone, suggestive of shallow afterslip that however does not reach the surface. Concurrent net 10-15 mm horizontal motions are measured at continuous GPS sites, with amplitude that diminishes slowly with distance from the mainshock rupture, suggestive of deeper afterslip or viscoelastic relaxation. Further observations over the coming months and years will clarify the relative roles of these postseismic processes and how they vary with time.