T169 Integrated Geologic and Chronometric Insights into Tectonic Processes at Plate Boundaries

Tuesday, 24 September 2024
8:00 AM - 12:00 PM
304C

EVIDENCE OF ACTIVE REVERSE FAULTING AND A LEFT-STEPPING SAN ANDREAS FAULT (MISSION CREEK STRAND) IN THE EASTERN SAN BERNARDINO MOUNTAINS, SOUTHERN CALIFORNIA

Paper number: T169-4
Program: Technical Sessions
Time: 8:40 AM – 8:55 AM

Authors

Abstract

This study presents a revision of mapped faults of the southern San Andreas fault, specifically the Mission Creek strand, at the latitude of northern Coachella Valley from Mission Creek to Whitewater River. Previous studies in the region indicate that as the San Andreas fault splits into the Mission Creek, Banning, and Garnet Hill strands in the Indio Hills, the Banning strand accommodates the majority of displacement across the plate boundary and forms a structurally complex zone with the Garnet Hill strand and San Gorgonio Pass fault zone, while the Mission Creek is mapped as inactive. However, a recent provenance study of displaced Quaternary sediment and 36Cl/10Be burial dating indicate recent fault activity on the Mission Creek strand during the mid to late Pleistocene. Field mapping at the onset of the left-restraining bend of the Mission Creek strand reveals a series of faults that offset geomorphic features in Quaternary alluvium and deform local bedrock. These faults have: (1) tilted and uplifted a middle Pleistocene alluvial fan complex; (2) preserved dip-slip displacement in mid to late Pleistocene fan surfaces along fault scarps; and (3) laterally offset stream channels that were incised during the latest Pleistocene and Holocene. Most interestingly, we observe laterally offset ridges, drainages, and debris flows along an unmapped trace of the Mission Creek strand. These observations allow for a revised interpretation of fault evolution for the San Andreas fault in the northern Coachella Valley region of southern California.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404584

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