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Constraining Long-Term Sediment Depositional History at Ancient Lake Cahuilla, Coachella, California

Marina O. Argueta, Sourav Saha, Seulgi Moon, Nathan D. Brown, Thomas K. Rockwell, Katherine M. Scharer, J Leidelmeijer, & Z Morgan

Published 2021, SCEC Contribution #13403

The depositional history of the Salton Sea region provides a rich frameworkfor understanding the timing of paleoearthquakes along the southern SanAndreas fault and the lake level history of Lake Cahuilla (LC). Previoustrenching investigations determined that the average recurrence interval ofthis portion of the San Andreas fault is ~200 years. The most recent ground-rupturing earthquake within this area happened about 300 years ago,coinciding with the last highstand of LC. Some studies have proposed thatLC perturbs the regional stress fi eld and large earthquakes correlate to lakefi lling events. However, this relationship is diffi cult to distinguish due to limitedtemporal records (only the past 1 ka with a 7-8 m deep trench) andconfl icting stratigraphic interpretations. In this study, we collected twocontinuous boreholes, 33.5 and 40 m deep, from the Coachella paleoseismicsite along the southern San Andreas fault. The 33.5-m-deep core wascollected at 9 m elevation near a ~12-m-high shoreline of LC within a smallstructural depression at the site. The second, 40-m-deep borehole, wascollected 135 m southwest of the fi rst borehole, outside of the deformationzone of the San Andreas fault. With these borehole samples, we interpret along-term sedimentary history of the ancient Lake Cahuilla. We also examinethe timing and frequency of major phases of sediment supply, aggradation,and hiatuses from layers in the cores. Our preliminary results show thatborehole logs extend the long-term sedimentation history at this site to ≥ ~6ka, and these two boreholes exhibit somewhat different sedimentarycharacteristics. Our work contributes to further understanding ofpaleoseismic studies of the southernmost San Andreas fault related to long-term lake fi lling history in southern California.

Argueta, M. O., Saha, S., Moon, S., Brown, N. D., Rockwell, T. K., Scharer, K. M., Leidelmeijer, J., & Morgan, Z. (2021). Constraining Long-Term Sediment Depositional History at Ancient Lake Cahuilla, Coachella, California. Poster Presentation at AGU Fall Meeting.