SCEC Award Number 15182 View PDF
Proposal Category Individual Proposal (Special Fault Study Area)
Proposal Title Slip Rate of the Banning Fault at Mission Creek
Name Organization
Sally McGill California State University, San Bernardino
Other Participants Lewis Owen (dating collaborator)
SCEC Priorities 1a, 4a, 4b SCEC Groups SoSAFE, Geology, WGCEP
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
To better understand the likely rupture paths and slip distribution in future earthquakes on the southern San Andreas fault, additional slip rate measurements are needed from the Mission-Mill Creek, Banning and Garnet Hill strands of the San Andreas fault in northern Coachella Valley. Work is in progress at a new slip rate site on the Banning fault, where an ancient channel wall of Mission Creek has been offset 148 ± 9 m by the Banning fault. During 2015, after a lengthy permitting process, permission was obtained to excavate dating pits, and three pits were excavated at the site in January 2016. Two 2-m deep pits were excavated on the old fan surface into which Mission Creek incised, and one 1.5-m deep pit was excavated into the alluvial deposits that post-date the incision, but that have been offset out of the path of the modern channel. Twelve samples for optically stimulated luminescence dating were collected by Dr. Lewis Owen (4 samples from each pit), as well as seven samples from each of the two deeper pits for Be-10 depth profiles. These are being processed at the Geochronology Laboratories at the University of Cincinnati under the direction of Lewis Owen. Twelve charcoal samples were also collected for radiocarbon dating. Processing of these samples has begun, and dates are expected before the end of 2016. The dates will constrain the age of incision of the offset channel wall, which can then be used to estimate the slip rate for this part of the Banning fault.
Intellectual Merit The early Holocene or latest Pleistocene slip rate that will be obtained for the Banning fault as a result of this work will increase our understanding of how the southern San Andreas fault system works, in terms of partitioning of slip between various faults and various strands of the San Andreas fault, and in terms of changes in slip rate over time.
Broader Impacts One undergraduate and one graduate student were hired to assist with the field work for this project. Sally McGill presented a public lecture on her research on the San Andreas fault to an audience of 200 at the Rancho Mirage public library (in a community near the field site where this study was conducted) on March 15, 2016. Post-doctoral researcher, Paula Marques Figueriedo at the University of Cincinnati is learning how to undertake OSL and Be-10 cosmogenic dating using the samples we collected for this study.
Exemplary Figure Figure 2: Lidar image (a) and geologic map (b) of the Banning fault slip rate site, showing west edge of Mission Creek offset 150 meters. (S. McGill).