SCEC Award Number 21100 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Constraining a long-term paleolake and paleoseismic history using deep boreholes at the ancient Lake Cahuilla, Coachella, California
Name Organization
Seulgi Moon University of California, Los Angeles Sourav Saha University of California, Los Angeles Thomas Rockwell San Diego State University Katherine Scharer United States Geological Survey
Other Participants Nathan D. Brown, University of Texas at Arlington,
Marina Argueta, Graduate student at UCLA
SCEC Priorities 5b, 5c, 5d SCEC Groups Geology, SAFS
Report Due Date 03/15/2022 Date Report Submitted 06/21/2022
Project Abstract
To estimate the cumulative vertical displacement recorded at Coachella structural depression(CSD), we previously collected a ~33.5-m (CSD) core and now extracted another ~35-m-deep borehole just outside the CSD near Mesquite sand dune (MSD), away from SSAF in June 2021. We referred to this core as the MSD core. The detailed stratigraphic log of the borehole suggests approximately 31 lake highstands (water-lain clay/silt rich units), interrupted by sandy units of the fluvial, deltaic, and recessional bar origin. Using 13 luminescence and 13 C-14 samples from the sandy and clayey units from the CSD core, respectively, and five new luminescence ages from the MSD core, we are constraining the lake desiccation and highstand cycle of the ancient Lake Cahuilla. The corrected luminescence ages show promise. However, luminescence ages for the MSD core require additional dating, rigorous fading, and dose rate experiments to account for the apparent stratigraphic age inversion. Further, to quantify the variations in the MSD stratigraphy and estimate the water content, we plan to perform an extensive grain size and shape analysis across the borehole at SDSU's Quaternary Geology Lab. We also plan to date organic matters from the MSD core for C-14 dating at UC Irvine. Our preliminary age model for the ancient Lake Cahuilla offers the longest lake history (~10.5 ka) to date, including a wealth of structural information associated with the movement on the southern San Andreas Fault.
Intellectual Merit The project offers the longest lake filling and desiccation cycles of the ancient Lake Cahuilla in the Salton Trough. These results are crucial to test whether SSAF is susceptible to lake loading and associated porewater pressure or is just a mere coincidence. In addition, the project has the intellectual merit of offering long-term sedimentologic context for paleoearthquake and slip rate studies in the Coachella Valley. In combination with geotechnical data (e.g., CPT), borehole data also has the potential to estimate the cumulative vertical displacement at the Coachella site. The new luminescence chronology and analytical improvements are valuable for providing a means to date deep borehole sediments, especially in contexts where no organic material for 14C exists, or the 14C ages are enormously affected by inheritance or reservoir effect.
Broader Impacts This project has provided ample opportunities for research and training at UCLA, SDSU, & CSUF. The project helps develop a series of other projects for the postdoctoral fellow at the University of Kentucky. A graduate and two undergraduate students are also being trained under this project. This project is part of a Ph.D. thesis at UCLA and two undergraduate research projects at SDSU and CSUF. Besides, the project contributes directly to addressing three primary goals of SCEC5: Science Objectives of "P5.b.", "P5.c.", and "P5.d."
Exemplary Figure Figure 3