Geodetic constraints on frictional properties and earthquake hazard in the Imperial Valley, Southern California

Abstract

We analyze a suite of geodetic observations across the Imperial Fault in southern California that span all parts of the earthquake cycle. Coseismic and postseismic surface slips due to the 1979 M 6.6 Imperial Valley earthquake were recorded with trilateration and alignment surveys by Harsh (1982) and Crook et al. (1982), and interseismic deformation is measured using a combination of multiple interferometric synthetic aperture radar (InSAR)‐viewing geometries and continuous and survey‐mode GPS. In particular, we combine more than 100 survey‐mode GPS velocities with InSAR data from Envisat descending tracks 84 and 356 and ascending tracks 77 and 306 (149 total acquisitions), processed using a persistent scatterers method. The result is a dense map of interseismic velocities across the Imperial Fault and surrounding areas that allows us to evaluate the rate of interseismic loading and along‐strike variations in surface creep. We compare available geodetic data to models of the earthquake cycle with rate‐ and state‐dependent friction and find that a complete record of the earthquake cycle is required to constrain key fault properties including the rate‐dependence parameter (a − b) as a function of depth, the extent of shallow creep, and the recurrence interval of large events. We find that the data are inconsistent with a high (>30 mm/yr) slip rate on the Imperial Fault and investigate the possibility that an extension of the San Jacinto‐Superstition Hills Fault system through the town of El Centro may accommodate a significant portion of the slip previously attributed to the Imperial Fault. Models including this additional fault are in better agreement with the available observations, suggesting that the long‐term slip rate of the Imperial Fault is lower than previously suggested and that there may be a significant unmapped hazard in the western Imperial Valley.

Geodetic Evidence for a Blind Fault Segment at the Southern End of the San Jacinto Fault Zone

“…This is higher than the upper bound of 6 mm/yr suggested by Hudnut and Sieh (1989) based on the offsets in the beach deposits of Lake Cahuilla. The rate of shallow creep on the Superstition Hills fault of 1.3 mm/yr (or higher, if slow slip events are included) (Wei et al, 2009) is too high to be consistent with the geologic slip rate of 2-6 mm/yr estimated by Hudnut and Sieh (1989) but appears to be consistent with the slip rate suggested by our inversions given that rates of shallow creep are typically an order of magnitude smaller than the interseismic slip rates at depth 10.1002/2017JB014477 (e.g., Lindsey & Fialko, 2016;Kaneko et al, 2013). The rate of shallow creep on the Superstition Hills fault of 1.3 mm/yr (or higher, if slow slip events are included) (Wei et al, 2009) is too high to be consistent with the geologic slip rate of 2-6 mm/yr estimated by Hudnut and Sieh (1989) but appears to be consistent with the slip rate suggested by our inversions given that rates of shallow creep are typically an order of magnitude smaller than the interseismic slip rates at depth 10.1002/2017JB014477 (e.g., Lindsey & Fialko, 2016;Kaneko et al, 2013).…”

“…To mitigate this limitation, a combination of data from two or more lines of sight can be used for the separate estimation of horizontal and vertical displacements (Fialko et al, 2002(Fialko et al, , 2005(Fialko et al, , 2001Lindsey & Fialko, 2016;Wright et al, 2004). To mitigate this limitation, a combination of data from two or more lines of sight can be used for the separate estimation of horizontal and vertical displacements (Fialko et al, 2002(Fialko et al, , 2005(Fialko et al, , 2001Lindsey & Fialko, 2016;Wright et al, 2004).…”

Earthquake Nucleation on Faults With Heterogeneous Frictional Properties, Normal Stress

“…Seismological and geodetic observations have also been used to infer variations of frictional properties. Geodetic inferences include inversion for the magnitude of the direct and evolution effects or steady state rate dependence, which indicate variations of each at the crustal scale (Jolivet et al, 2013;Kaneko et al, 2013;Lindsey & Fialko, 2016), and also include patterns of interseismic coupling suggesting transitions between rate-strengthening and rate-weakening behavior, again on the crustal scale (e.g., Chlieh et al, 2008;Jolivet et al, 2015;Kaneko et al, 2010;Perfettini et al, 2010;Villegas-lanza et al, 2016). Finer-scale variations are suggested by seismological observations, which include precise relocations of microseismicity (e.g., Rubin et al, 1999;Waldhauser et al, 2004) that show clustering interspersed by comparatively quiescent regions.…”

Slow Slip Event On the Southern San Andreas Fault Triggered by the 2017 Mw8.2 Chiapas (Mexico) Earthquake

“…A number of active continental strike-slip faults are associated with geodetically detectable shallow creep, while other faults (or other sections of the same fault) appear to be locked all the way to the surface over the interseismic period (e.g., Cakir et al, 2005;Harris, 2017;Lindsey, Sahakian, et al 2014;Lindsey & Fialko, 2016;Savage & Lisowski, 1993;Simpson et al, 2001). Traditional interpretations of shallow creep in terms of the conditionally stable or velocity-strengthening (VS) friction in the uppermost crust predict that shallow creep should occur at a quasi-constant rate throughout much of the earthquake cycle (e.g., Kaneko et al, 2013;Li & Rice, 1987;Lindsey & Fialko, 2016;Marone & Scholz, 1988). However, geodetic observations indicate that faults that exhibit shallow creep also often host episodic accelerated creep events (e.g., Bilham et al, 2016;Goulty & Gilman, 1978;Jolivet et al, 2015;Linde et al, 1996;Murray & Segall, 2005;Wei et al, 2009;Shirzaei & Bürgmann, 2013), similar to the extensively studied episodic slow slip at the bottom of seismogenic megathrusts in subduction zones (Obara et al, 2004;Rogers & Dragert, 2003;Schwartz & Rokosky, 2007).…”