USING CREEP RELATED FEATURES AND GEODETIC ANALYSES TO DEFINE THE LOCATION, SLIP RATE, AND GEOMETRY OF OFF FAULT DEFORMATION, HIDDEN SPRING FAULT ZONE, SOUTHERN CALIFORNIA

The slip rate between the North American and Pacific plates is ~48.4 mm/yr, yet only ~ 22 mm/yr is accommodated on the Southern San Andreas Fault (SSAF). Thus, the remaining strain must be accommodated elsewhere. Geodetic models suggest, in addition to faults west of the SSAF, faults east of the SSAF may accommodate right-lateral motion. We investigate the role of the Hidden Spring Fault Zone (HSFZ), and related structures east of the SSAF in accommodating some of this slip. Field studies suggest the HSFZ forms a ladder structure south of the projected intersection with the Salton Creek Fault, where it is up to 10 km wide, and accommodates an uncertain amount of tectonic slip from the SSAF. We integrate a range of image analyses methods to examine the evidence for active faults in the area. Preliminary analyses of UAVSAR data, using edge detection methods, which detect phase jumps associated with triggered fault slip, are paired with geologic observations from enhanced natural and false color images. These data reveal the HSFZ consists of a series of left-lateral and oblique cross faults between right-lateral master faults, such as the HSF to the west, and several left-stepping faults that include the Hot Spring Fault to the east. These two master faults bound a complex mesh of right and left-lateral structures, NE-striking cross faults, and incipient fault-folds. Remote image analysis of natural and false color images, generated from NAIP data, reveal a number of small faults east of the HSF, evidenced by truncated and displaced beds, zones of uplift and subsidence, ground cracks and vegetation lineaments made visible by image manipulation. Mapping these features in ESRI’s ArcMap allows us to effectively compare their location and expression over varying ages and types of visual data including NAIP, satellite and historical imagery, as well as geologic maps, UAVSAR and other references. These varied datasets allow us to create an integrated model of the precise location of the HSFZ, the amount and nature of slip distribution on faults associated with the SSAF, as well as allowing us to conduct a kinematic analysis of the HSFZ. We examine how faults in the region experienced triggered slip from distant earthquakes and are establishing a baseline analysis of deformation in a region where large seismic ruptures very will occur.