Dates of the Two Most Recent Surface Ruptures on the Southernmost San Andreas Fault Recalculated by Precise Dating of Lake Cahuilla Dry Periods

Thomas K. Rockwell, Aron J. Meltzner, & Erik C. Haaker

Published July 17, 2018, SCEC Contribution #7970

The past two southernmost San Andreas fault (SAF) ruptures occurred when ancient Lake Cahuilla was full, or nearly so, based on extensive liquefaction at sites near the shoreline. The timing of the past two southern SAF ruptures have been re-evaluated with new radiocarbon data on in situ stumps that grew between the past three Lake Cahuilla highstands. 14C dates on inner and outer rings combined with historical observations show that the dry period prior to the last lake occurred between about CE 1650 and 1706, leaving a very narrow window of less than 20 years to fill and begin desiccating the most recent lake. The timing of the most recent event advances to CE 1726+7, whereas the timing of the penultimate event is slightly older at ca CE 1605. These new dates, when combined with previous age estimates of earlier southern SAF events, suggest more regular recurrence of surface-rupturing events, with an average interval of about 200 years, but leaves the open interval at about 300 years.

Key Words
San Andreas paleoseismology, Lake Cahuilla

Citation
Rockwell, T. K., Meltzner, A. J., & Haaker, E. C. (2018). Dates of the Two Most Recent Surface Ruptures on the Southernmost San Andreas Fault Recalculated by Precise Dating of Lake Cahuilla Dry Periods. Bulletin of the Seismological Society of America, 108(5A), 2634-2649. doi: 10.1785/0120170392.