SPATIAL, STRUCTURAL, AND TEMPORAL CHARACTERISTICS OF NEOTECTONIC SURFACE-DEFORMATION WITHIN INTERACTING MULTI-FAULT SYSTEMS IN THE SOUTHERN DEATH VALLEY AND TWENTYNINE PALMS AREAS OF SOUTHERN CALIFORNIA, USA

Geologic and geomorphic mapping, combined with geochronologic investigations, reveal spatial, structural, and temporal patterns on interacting multi-fault systems within the Eastern California Shear Zone (ESCZ). Quaternary deformation in the southern Death Valley (SDV) and Twentynine Palms (TP) study areas is dominated by several NW-oriented dextral and dextral-oblique faults that complexly intersect with a single major transversely oriented EW-striking sinistral- to sinistral-oblique fault. In SDV, a 50 km-long section of the sinistral eastern Garlock Fault (EGF) traverses to the E along the southern edge of a domain of two mutually intersecting transcurrent faults (including the SE-end of the NW-trending dextral Southern Panamint Valley Fault) near the Owlshead Mountains. The EGF terminates to the E against a continuous trace of the NW-trending dextral-oblique SDV Fault. Individual faults within the domain N of the EGF don’t directly cross-cur or displace each other or the EFF. They tend to conjugately merge with or abut against one another within these localized areas of intersection. The continuous trace of the EGF deflects or branches stepwise to the SSE at these intersection zones. Individual faults within intersection zones preferentially contain pronounced zones of secondary transpression consisting of complex arrays of uplifted and rotated fault-bounded blocks and fault propagation folds. Stratigraphic timing constraints between exposed fault structures and dated surficial deposits indicate systematic progressive-strain transfer and accumulation among these faults systems throughout much of the Quaternary. A similar pattern is observed in detailed studies of a set of intersecting transcurrent faults in the TP area. A 40-km section of the E-oriented sinistral Pinto Mountain Fault (PMF) traverses to the ESE via a successively wider and more complex set of oblique slip fault-strands. These segments are associated with increased secondary transpressive deformation occurring near intersections with several NW-trending dextral faults to the N (including the Mesquite Lake Fault, MLF). Detailed mapping and geochronologic data permit recognition of one or more specific individual surface ruptures with similar displacements and timing relations on the PMF and MLF, suggesting possible coeval triggering of paleoearthquakes on both structures.