Geodetic observations of fault creep in the Imperial Valley: hidden faults, earthquake hazard and implications for frictional properties

Abstract:

We present new observations of the pattern of fault creep and interseismic deformation in the Imperial Valley, California using a combination of multiple InSAR viewing geometries and survey-mode GPS. We combine more than 100 survey-mode GPS velocities (Crowell et al., 2013) with Envisat InSAR observations from descending tracks 84 and 356 and ascending tracks 77 and 306 (149 total acquisitions), processed using the Stanford Method for Persistent Scatterers (StaMPS) package (Hooper et al., 2007). The result is a dense map of surface velocities across the Imperial fault and surrounding areas. The data suggest that a previously little-known extension of the Superstition Hills fault through the town of El Centro may accommodate a significant portion of the slip previously attributed to the Imperial Fault. We investigate a suite of possible models for the transfer of this slip to the Imperial and Cerro Prieto faults to the south, yielding a range of plausible hazard scenarios. Finally, we compare the geodetic data to models of earthquake cycles with rate- and state-dependent friction to assess the implications for creep depth, moment accumulation rate, and recurrence interval of large events on these faults.