Mapping fault creep, frictional properties, and unrecognized active structures with dense geodetic data in the Imperial Valley, Southern California

Eric O. Lindsey, & Yuri Fialko

Published September 6, 2016, SCEC Contribution #6832, 2016 SCEC Annual Meeting Poster #129 (PDF)

The Imperial-Mexicali valley is well known as an area of significant earthquake hazard, but it remains a challenging target for geodetic studies because of agricultural and geothermal activity which obscures both short- and long-term deformation and can lead to aquifer-related contamination of the geodetic signals. We address these difficulties by combining InSAR data from four independent Envisat tracks, processed using a persistent scatterers method, to separate the vertical and horizontal (fault-parallel) motion. We combine these data with coseismic and postseismic geodetic observations of the 1979 M 6.6 Imperial Valley earthquake (Harsh, 1982 and Crook et al., 1982) and dense interseismic GPS velocities (Crowell et al., 2013). The result is a dense map of geodetic observations spanning nearly a complete earthquake cycle on the Imperial fault, which allows us to evaluate the rate of interseismic loading and along-strike variations in surface creep. We compare the data to dynamic models with rate- and state-dependent friction and show 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.

In addition, we show 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. Such a fault has previously been proposed (Thomas & Rockwell, 1996 and Hogan et al., SCEC abstract, 2002). Dislocation 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.

Key Words
Imperial fault, friction, interseismic, earthquake cycle

Citation
Lindsey, E. O., & Fialko, Y. (2016, 09). Mapping fault creep, frictional properties, and unrecognized active structures with dense geodetic data in the Imperial Valley, Southern California. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Southern San Andreas Fault Evaluation (SoSAFE)