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Trenching the causative faults of the 2019 Ridgecrest sequence

Ian Pierce, Alana M. Williams, Rich D. Koehler, & Ramon Arrowsmith

Published August 10, 2021, SCEC Contribution #11246, 2021 SCEC Annual Meeting Poster #060

The 2019 Ridgecrest earthquake sequence consisted of a M6.4 rupture along the Salt Wells Valley left-lateral strike-slip fault on July 4th, 2019, followed by a M7.1 rupture of the nearly perpendicular Paxton Ranch right-lateral strike-slip fault on July 5th, 2019. Here we chose three sites, two along the Paxton Ranch fault and one along the Salt Wells Valley fault to investigate the paleoseismic rupture history of each of these faults. We excavated five trenches among the three sites. Each trench exposed evidence of past earthquake ruptures, although the timing remains uncertain pending dating results. The clearest event chronology was exposed in the trench at the basin site along the southern part of the Paxton Ranch fault, and showed clear evidence for at least two prior latest Pleistocene/Holocene surface rupturing events, with vertical displacements similar to the 2019 event. Assuming that the ~120 cm dextral displacement from the most recent event at this site was similar for each of these three total events and an estimate age of the oldest deposits based on the age of pluvial Searles Lake (~12 ka), we estimate a local slip rate of 0.3 mm/yr for the southernmost part of the fault. Due to the lower depositional rates at the other sites, unraveling a specific event chronology in the other trenches has proven challenging, however, future dating results will provide broad time constraints on prior deformation.

Pierce, I., Williams, A. M., Koehler, R. D., & Arrowsmith, R. (2021, 08). Trenching the causative faults of the 2019 Ridgecrest sequence. Poster Presentation at 2021 SCEC Annual Meeting.

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Earthquake Geology