Late Breaking Session: Ten-Million Years of Deformation along the Eastern California Shear Zone: Context and Characterization of the July 2019 Mw7.1 Ridgecrest Earthquake

Sunday, 22 September 2019
1:45 PM - 5:30 PM
North Ballroom 120D, North Building

RELATIVE PATTERNS OF NEOTECTONIC DEFORMATION ALONG THE EASTERN GARLOCK AND EASTERN PINTO MOUNTAINS FAULT ZONES: TWO DOMAIN-BOUNDING TRANSVERSE STRUCTURES WITHIN THE EASTERN CALIFORNIA SHEAR ZONE

Program: Late Breaking
Time: 2:35 PM – 2:50 PM

Authors

Abstract

The Garlock (Gf) and Pinto Mountain (PMf) faults are two major E-trending sinistral fault zones that traverse across the NW-trend of the Eastern California Shear Zone (ECSZ) in south-central California. Both faults have eastern sections that are similar in terms of tectonic landscape: the fault sections separate contrasting regional neotectonic domains to the N and S; (a) low-elevation terranes with abutting sets of NW-trending dextral faults to the N vs. (b) upland areas with subparallel sets of E-striking sinistral faults to the S. Eastern Gf: The 50-km-long easternmost section of the Gf broadly curves from an ENE to E orientation in a psuedo-oroclinal bend via discrete branches and en-echelon stepovers. Reorientation is accompanied by stepwise E-ward increases in fault-zone width, structural complexity, and secondary transpressive structures that are prominent near intersections with dextral faults from the N. A core concentated zone of multistrand surface ruptures (fault scarps, shutter ridges, deflected streams) of mixed Pleistocene to late Holocene age with poorly-constrained slip-rate estimates of 6-1.5 mm/yr. is embedded in a wider less active fault zone that both terminate eastward into splays westward of range-bounding thrust faults of the Avawatz Mountain on the E-boundary of the ECSZ. Eastern PMf: The eastern PMf extends 25 km from Joshua Tree to Twentynine Palms between a zone of NW-trending dextral faults on the south edge of the Mojave Desert to the N, and a high-relief N-range front of the Eastern Transverse Ranges with E-trending sinistral faults to the S. The PMf trend deflects incrementally from E to SE via a series of southward-younging branches, splays, and right steps in the composite fault zone. Reoriented strands also are accompanied by E-ward increases in fault-zone width, internal complexity, and number of fault strands; major secondary transpressive popup structures occur near intersections with dextral faults to the N. Tectonic features (fault scarps, shear zones, deflected streams, faulted ridges) indicate distributed zones of late Pleistocene to late Holocene surface ruptures, with slip-rate estimates of 1.5 to 2 mm/yr. The compound PMf zone ends where it intersects the Mesquite Lake dextral fault on the E border of the core ECSZ, although an older PMf segment continues 30 km further E.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-340629

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