Paper No. 132-7
Presentation Time: 9:35 AM
FORE-LIMB AND BACK-LIMB FOLDING OF THE PUENTE HILLS BLIND-THRUST FAULT WITH IMPLICATIONS FOR PLEISTOCENE-HOLOCENE SLIP-RATE ESTIMATES AND SEISMIC HAZARD ANALYSIS IN THE LOS ANGELES BASIN, SOUTHERN CALIFORNIA
Using a combination of high-resolution and industry seismic reflection profiles, historical well logging data, and luminescence and 14C ages, we determine a detailed Pleistocene-Holocene slip history for the Santa Fe Springs segment of the Puente Hills blind-thrust fault (PHT), beneath metropolitan Los Angeles. Deep thrust displacement on the PHT is consumed updip in the creation of a hanging-wall fault-bend fold. We analyze the geometry of correlative stratigraphic units in the fore-limb and back-limb of this fold, using seismic reflection data and drilling data, and determine the uplift of several discrete units. These uplift measurements are converted to thrust displacements on the underlying PHT using a novel structural method, developed by Don et al. (in Review), that accounts for the precise geometry of the fault surface. Historical well logs, luminescence ages, and 14C ages collected from growth strata on the fore-limb and back-limb provide age constraints for folding and thrusting on the underlying PHT. A comparative slip history for the fore-limb and back-limb fold is determined from at least four discrete growth horizons, recording incremental deformation rates at four time intervals spanning the past ca. 450 ka. This study provides a direct comparison of fore-limb and back-limb slip rates determined for the same structure, facilitating accurate determination of the proportion of thrust displacement that is consumed in the development of different parts of the hanging-wall fold. Additionally, these new data provide more detailed constraints on both average slip rate of the PHT, a major seismic threat to the highly urbanized Los Angeles metropolitan region, as well as the variability of slip rate through time on this large thrust fault. These slip-rate data will also facilitate comparisons with similar rate data from other faults within the southern California plate boundary fault network.