SCEC Award Number 14202 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Collaborative Research: Completing the past 500 years of paleoearthquakes at the Elizabeth Lake paleoseismic site, Mojave section of the southern San Andreas fault
Investigator(s)
Name Organization
Sean Bemis University of Kentucky James Dolan University of Southern California Katherine Scharer United States Geological Survey Edward Rhodes University of California, Los Angeles
Other Participants 4 students - 2 UK and 2 USC
SCEC Priorities 2a, 4c, 4b SCEC Groups USR, SoSAFE, Geology
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 The extent of paleo-ruptures of the Mojave section of the San Andreas Fault has been hampered by a lack of paleoseismic sites on a 100-km-long stretch of the fault between the Frazier Mountain and Pallett Creek sites. This study continues to target the Elizabeth Lake paleoseismic site, where prior studies were completed in 1999, 2012, and 2013. In total, our paleoseismic investigations consist of 10 trenches that cross a 40-m by 350-m fault-parallel depression containing a ~2000 year depositional record. Investigations during 2014 focused on documentation of two new trenches as well as the expansion of three 2013 trenches to provide additional exposures across the key eastern portion of the site where the fault zone projects through an area of relatively continuous sediment accumulation from a north-flowing wash. These trenches reveal the thickest section of young stratigraphy found at the site and the widest fault zone. Faulting patterns here show that over the last ~800 years, a 3-m-wide pop-up caused fluvial sand and gravel deposits and organic-rich pond deposits to interfinger south of the fault while a thick organic-rich loam accumulated on the north side of the pop up. Faulting, fissures, and tilted blocks provide evidence for 4 to 5 paleo-earthquakes since ca. 1250 A.D. Radiocarbon dating established that the site has a significant component of detrital charcoal that can be 500 years older than other charcoal samples in the same layer, so additional samples, including ones for post-IR IRSL luminescence dating, are being processed to establish true layer ages.
Intellectual Merit The Elizabeth Lake paleoseismic site contains the best remaining potential to provide key constraints on the extent and frequency of prehistoric ruptures along the Mojave section of the southern San Andreas fault. Completing this record for the past 5+ paleoearthquakes is critical for providing the best possible along-fault earthquake chronology to test models of earthquake recurrence.
Broader Impacts By providing limits on the potential rupture extent of prehistoric earthquakes along the southern San Andreas fault, our research at the Elizabeth Lake paleoseismic site will provide important parameters for seismic hazard assessment by constraining the frequency at which large (~M8) earthquakes have ruptured this portion of the fault. Our work at the site has been highly collaborative, integrating 6 undergraduate and graduate student researchers from 4 different universities during 2014. These students were involved in all aspects of the paleoseismic research, providing training in surveying, photogrammetry, Quaternary geochronology, Quaternary stratigraphy, and soft-sediment structural geology. Our SCEC intern, Crystal Wespestad, participated in the full 3 weeks of fieldwork at the site as well as assisting with in post-fieldwork data processing and synthesis.
Exemplary Figure Trench EL4.2E