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, Zoe Morgan, & Jenifer Leidelmeijer

Published August 13, 2021, SCEC Contribution #11350, 2021 SCEC Annual Meeting Poster #088

The depositional history of the Salton Sea region provides a rich framework for understanding the timing of paleoearthquakes along the southern San Andreas fault and the lake level history of Lake Cahuilla (LC). Previous trenching investigations determined that the average recurrence interval of this 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 that LC perturbs the regional stress field and large earthquakes correlate to lake filling events. However, this relationship is difficult to distinguish due to limited temporal records (only the past 1 ka with a 7-8 m deep trench) and conflicting stratigraphic interpretations. In this study, we collected two continuous boreholes, 33.5 and 40 m deep, from the Coachella paleoseismic site along the southern San Andreas fault. The 33.5-m-deep core was collected at 9 m elevation near a ~12-m-high shoreline of LC within a small structural depression at the site. The second, 40-m-deep borehole, was collected 135 m southwest of the first borehole, outside of the deformation zone of the San Andreas fault. With these borehole samples, we interpret a long-term sedimentary history of the ancient Lake Cahuilla. We also examine the timing and frequency of major phases of sediment supply, aggradation, and hiatuses from layers in the cores. Our preliminary results show that borehole logs extend the long-term sedimentation history at this site to ≥ ~6 ka, and these two boreholes exhibit somewhat different sedimentary characteristics. Our work contributes to further understanding of paleoseismic studies of the southernmost San Andreas fault related to long-term lake filling history in southern California.

Key Words
paleoseimicity, San Andreas fault, borehole

Citation
Argueta, M. O., Saha, S., Moon, S., Brown, N. D., Rockwell, T. K., Scharer, K. M., Morgan, Z., & Leidelmeijer, J. (2021, 08). Constraining long-term sediment depositional history at ancient Lake Cahuilla, Coachella, California. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
San Andreas Fault System (SAFS)