The Postseismic Deformation of the 6 July 2019 Mw 7.1 Ridgecrest Earthquake from Burst Overlap Interferometry, InSAR, and GNSS

Abstract

Abstract The July 2019 Ridgecrest earthquake sequence consists of an Mw 6.4 foreshock and an Mw 7.1 mainshock, which ruptured a complex set of orthogonal faults in the eastern California shear zone. We measure the co- and postseismic deformation associated with this sequence using the Burst Overlap Interferometry (BOI) technique in addition to the commonly used Interferometric Synthetic Aperture Radar (InSAR). The BOI technique, which provides displacement in the satellite’s along-track direction, offers important information on the postseismic deformation that cannot be measured by traditional InSAR and is only sparsely measured by the Global Navigation Satellite System networks. The BOI data reveal up to 4 cm displacement in the along-track direction, 10 km north of the northern tip of the seismic rupture, and up to 3 cm displacement along the coseismically active faults. These results rule out the possibility of significant shallow afterslip near the mainshock hypocenter, suggesting that the previously suggested poroelastic rebound is likely to be the cause for the significant postseismic line of sight deformation near the mainshock rupture. Based on the aftershocks’ moment tensor distribution, surface rupture, and simple forward modeling, we propose that the postseismic deformation north of the Ridgecrest rupture is caused by an aseismic slip along a north-trending normal fault of the Ridgecrest rupture that was induced by the Ridgecrest earthquake. Furthermore, we observed that both deformation and seismic activity decay slower over time as the distance from the Coso geothermal area increases. This decay is influenced by the mechanical properties of the crust, which are affected by the increased heat flow at Coso and thus suppress deformation and seismicity, ultimately controlling their temporal evolution.