SLIP RATE AND HAZARD POTENTIAL OF THE LONG VALLEY FAULT ZONE NEAR MAMMOTH, CALIFORNIA

We report a preliminary dextral slip rate of the Long Valley fault zone, a newly discovered component of the Eastern California Shear Zone-Walker Lane (ECSZ-WL) that separates the Sierra Nevada microplate from the Basin and Range province. The Long Valley fault zone was previously mapped as part of a system of normal faults that cut into the volcanic tablelands between Mammoth and Bishop, California. Notably, the Long Valley fault zone passes within 1 km of Long Valley dam, an earthen dam constructed in 1941 as part of the Los Angeles aqueduct. Our new mapping of this region reveals dextral offset of a buried buttress unconformity by over 350 meters. We speculate that this offset feature is a product of normal faulting associated with the collapse of the Long Valley caldera 765,000 years ago. We also observe dextral offsets of the shoreline cliff that was produced from the highstand of Long Valley lake, hypothesized to have drained approximately 140,000 years ago. Based on these observations, the Long Valley fault zone has a minimum estimated rate of slip of roughly 0.5 mm/yr. Several previous studies suggest that rates of dextral fault slip measured from geology sum to less than the geodetic rate of right-lateral motion across the ECSZ-WL. Though the majority of right slip at the latitude of Long Valley steps to the east via the Mina Deflection, our observations show that dextral faulting also occurs close to the Sierra Nevada range front, carried on previously overlooked strike-slip faults such as the Long Valley fault zone. Ongoing research will focus on mapping faulting and offsets in further detail, and refining the age of the Long Valley lake highstand.