Slip rate and hazard potential of the Long Valley fault zone near Mammoth, CA

Yvonne J. Leon, & Michael E. Oskin

Published September 10, 2023, SCEC Contribution #12860, 2023 SCEC Annual Meeting Poster #068

The Long Valley fault zone is a newly recognized component of the Eastern California Shear Zone - Walker Lane, a region that separates the Sierra Nevada microplate from the Basin and Range province. Previously mapped as a part of a set of normal faults that cut into the volcanic tablelands between Mammoth and Bishop, California, the Long Valley fault is redefined as a dextral fault with an approximate slip rate of 0.5 mm/yr based on the following observations: New mapping of this region reveals a 350 meter dextral offset of a ENE-striking buttress unconformity cut into the Bishop Tuff. We interpret that this buttress formed by normal faulting induced by the collapse of the Long Valley Caldera 765,000 years ago. Dextral offset can also be observed along this same fault system within the nearby volcanic tablelands. Here, dextral offset along three fault strands affects the ancient shoreline cliff produced by the highstand of Long Valley Lake, hypothesized to have drained 140,000 years ago. Several previous studies suggest that the rate of dextral slip measured from geology sum to less than the geodetic rate of right-lateral motion across the Eastern California Shear Zone - Walker Lane. This discrepancy between geologic and geodetic slip rates could be attributed to overlooked structures such as the Long Valley fault zone. Notably, the Long Valley fault zone passes within 1 km of the Long Valley dam, the earthen dam that impounds Lake Crowley, constructed in 1941 as a part of the Los Angeles aqueduct system.

Citation
Leon, Y. J., & Oskin, M. E. (2023, 09). Slip rate and hazard potential of the Long Valley fault zone near Mammoth, CA. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology