Back-limb and fore-limb folding of the Puente Hills blind-thrust fault with implications for late Pleistocene slip-rate estimates and seismic hazard analysis in the Los Angeles Basin, southern California

Chris Anthonissen, Franklin D. Wolfe, Lorraine A. Leon, Jessica Don, James F. Dolan, John H. Shaw, Tammy M. Rittenour, Ed J. Rhodes, & Andrew Ivester

Published August 16, 2021, SCEC Contribution #11515, 2021 SCEC Annual Meeting Poster #074

We used a combination of high-resolution and industry seismic reflection profiles, historical well logging data, and luminescence and 14C ages to determine a detailed, late Pleistocene to present-day incremental slip rate record for the Santa Fe Springs Segment of the Puente Hills blind-thrust fault (PHT), beneath the city of Los Angeles. Seismic reflection and borehole data were used to analyze the geometry and uplift patterns of several discrete stratigraphic units across a growth fold overlying the PHT. Having determined the precise geometry of the fault surface and the overlying folded growth strata from seismic reflection data, we used fault-bend folding theory ( Suppe, 1983) together with a novel structural method developed by Don et al. (in Review) to convert the uplift measurements into thrust displacements on the underlying PHT fault. Luminescence ages and 14C ages collected from cores provide age constraints for the deposition of several late Pleistocene to Holocene growth strata across both the fore-limb and the back-limb of the fold. This, in turn, provides age constraints for determining the slip and slip rate on the PHT at two distinct locations, one associated with the upper tipline of the fault (associated with the forelimb) and a second at greater depth on the fault ramp (associated with the backlimb). In addition, geochronological data from older strata folded during thrust displacement on the PHT yield a mid- to late-Pleistocene incremental slip history for several growth intervals spanning the past 450 ka. Our study thus provides a detailed incremental slip history of the PHT, as well as a direct comparison of fore-limb and back-limb derived slip rates for the same structure, which allows us to determine the proportion of thrust displacement that is consumed in building the hanging-wall fault-bend fold that has developed above this blind thrust fault. These results provide constraints on both the average intermediate-term (late mid-Pleistocene) slip rate of the PHT, a major seismic threat to the highly urbanized Los Angeles metropolitan region, as well as constraints on the variability of slip rate through time on this large thrust fault. These slip-rate data will facilitate comparisons with similar rate data from other faults within the southern California plate boundary fault network.

Key Words
Paleoseismology, Blind-thrust faults, Puente Hills

Citation
Anthonissen, C., Wolfe, F. D., Leon, L. A., Don, J., Dolan, J. F., Shaw, J. H., Rittenour, T. M., Rhodes, E. J., & Ivester, A. (2021, 08). Back-limb and fore-limb folding of the Puente Hills blind-thrust fault with implications for late Pleistocene slip-rate estimates and seismic hazard analysis in the Los Angeles Basin, southern California. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology