SCEC Award Number 12097 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Long term slip-rate of the Banning strand of the southern San Andreas Fault at Devers Hill
Investigator(s)
Name Organization
Whitney Behr University of Texas at Austin Warren Sharp Berkeley Geochronology Center Dylan Rood University of California, Santa Barbara
Other Participants Tom Rockwell (UCSD), 1 MS student from the University of Texas Austin
SCEC Priorities 2a, 4a, 4c SCEC Groups SoSAFE, Geology, WGCEP
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 Very little is known about the relative rates of slip southeast of San Gorgonio Pass along the Banning strand of the San Andreas Fault, because the geologic slip rate in this region is entirely unconstrained. The goal of this project is to address the present knowledge gap of fault slip rates southeast of the San Gorgonio Pass region by examining several offset alluvial fans and a channel margin along the Banning strand of the southern San Andreas fault near Devers Hill, located approximately 2 kilometers southeast of San Gorgonio Pass (Figure 1). We are working to establish a slip rate at this site by using the B4 LiDAR data to quantitatively measure the fault offset, and by combining cosmogenic dating with U-series dating on pedogenic carbonate to establish the depositional age of the offset features. This work is thus far a collaborative effort between several academic institutions (UT Austin, BGC, UCSB, and CSUSD) and the USGS, and is being undertaken primarily by the PIs and a Ph.D. student based at UT Austin.
Intellectual Merit An issue of particular importance in predicting seismic hazard in southern California is the potential for large earthquakes generated on the Coachella Valley strand of the San Andreas fault (CVS-SAF) to propagate through the San Gorgonio Pass structural complexity, triggering slip on the San Bernardino strand of the SAF and possibly propagating into the Greater Los Angeles region. A valuable method of testing the accuracy of this rupture model involves comparing the rates of slip on different faults within and on either side of San Gorgonio Pass (SGP). However, very little is known about the relative rates of slip southeast of San Gorgonio Pass along the Banning strand of the CVS-SAF, because the geologic slip rate in this region is entirely unconstrained. The goal of this project is to address the present knowledge gap of fault slip rates southeast of the San Gorgonio Pass region by examining several offset alluvial fans and a channel margin along the Banning strand of the southern San Andreas fault near Devers Hill, located approximately 2 kilometers southeast of San Gorgonio Pass. This research is currently work-in-progress, but once completed, we will have a much better understanding of how much slip is transferred along the San Andreas into San Gorgonio Pass northwestwards, vs. how much slip is siphoned off onto faults within the Eastern California Shear Zone prior to reaching San Gorgonio Pass.
Broader Impacts This project is currently supporting two junior researchers (Behr & Rood) and two students (1 undergraduate and 1 Ph.D. student). Behr recently involved a UT undergraduate (Aaron Salin) in this project. Aaron is part of the Jackson School’s Undergraduate Honors Research Program, and will complete a senior thesis focused on cosmogenic dating at the Devers Hill site. Behr & Gold both attended the SCEC Annual Meeting in 2011. Gold participated in the pre-meeting SoSAFE fieldshop focused on field interpretation of geomorphic features, and gave a presentation on the applications of LiDAR to measuring fault offsets in the SoSAFE session at the SCEC meeting. Co-PI’s Sharp and Rood also attended the 2012 SCEC meeting and participated in SoSAFE activities and workshops during 2012.
Exemplary Figure Figure 1. Annotated B4 LiDAR images of the Devers Hill site. [A] Quaternary geologic map of the Devers Hill site showing the primary offset alluvial fan remnants Qoa1, Qoa2, and Qoa3. [B] and [C] show close-up views of the Qoa1 fan margins both north and south of the fault where it covers the Qoa2 deposit. [D] Our preferred reconstruction of the Qoa1 and Qoa2 fan surfaces, which indicates an offset of ~1.6 km. The reconstruction restores several geomorphic features of similar topographic expression that we are investigating as part of this project.