Poster #022, San Andreas Fault System (SAFS)
Reconstructing long-term subsidence and paleoseismic history of the ancient Lake Cahuilla along the southern San Andreas fault in Coachella, California
Poster Image:
Poster Presentation
2020 SCEC Annual Meeting, Poster #022, SCEC Contribution #10290 VIEW PDF
stages of lake fill. Due to a high sedimentation rate (~5 mm/year) in the Salton Trough near Coachella, the existing trench records only date back to ~1 ka. These stratigraphic and temporal limitations, coupled with conflicting interpretation of lake stratigraphies, make it challenging to evaluate whether the lack of surface rupture since the MRE on the SSAF is due to the extended dry period in the lake. Extending the paleoseismic record back to the Mid-Holocene or older provides chronologic data to test the relationship between lake filling history and earthquake cycles. We therefore extracted a 33.5-m-deep core from the Coachella site south of Avenue 44, Indio, using a CME-85 continuous coring rig. The core was drilled at a narrow (~30 m wide) structural depression near the shoreline of ancient Lake Cahuilla and therefore is poised to capture both the changes in lake filling and rupture/subsidence triggered by the movement along the SSAF. Detailed logs of this continuous core record the deep subsurface stratigraphic units and are used to guide sampling locations for geochronological dating. This core had ~85% recovery and consists of alternate lacustrine and subaerial units. We plan to measure 12 luminescence ages from the subaerial units to date lake regression events. This project aims to provide a crucial insight into the long-term: (i) lake filling/desiccation chronology, (ii) a subsidence history of the ancient Lake Cahuilla, and (iii) sedimentologic context for paleoearthquake and slip rate studies in the Coachella Valley.
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