SCEC Award Number 15135 View PDF
Proposal Category Collaborative Proposal (Special Fault Study Area)
Proposal Title Collaborative Research: High-precision cosmogenic burial and exposure dating (10Be, 26Al, 36Cl) on late Pleistocene fan surfaces to constrain long-term San Andreas fault slip rates
Investigator(s)
Name Organization
Richard Heermance California State University, Northridge Nathaniel Lifton Purdue University
Other Participants 1 CSU Northridge undergraduate, 1 Purdue University Graduate Student
SCEC Priorities 1a, 4a, 4b SCEC Groups SoSAFE, Geology, Seismology
Report Due Date 03/15/2016 Date Report Submitted 03/16/2016
Project Abstract
 The goal of this project is to determine the age of uplifted and deformed Quaternary surfaces between the Banning and Garnet Hill strands of the San Andreas Fault in the northern Coachella Valley, CA. Ages will be determined through cosmogenic nuclide (26Al/10Be) isochron burial dating of clasts within buried paleosols. Mapping of the of the Whitewater Hill area reveals at least 2 buried paleosols defining a long-term, mid-Pleistocene record of alluvial fan development. These paleosols can be used as piercing points to develop long-term (>100,000 year) slip rates along this section of the San Andreas fault system. Field work was completed from June 15 – July 15. We sampled both buried paleosols for cosmogenic nuclide isochron burial dating, for a total of 18 samples. Be and Al have both been extracted at PRIME Lab and are awaiting analysis by Accelerator Mass Spectrometry (AMS). We expect results within approximately the next month (April, 2016). The suite of AMS results from each paleosol will be ana-lyzed in terms of burial age using isochron techniques, which will then be used to infer uplift rates along the adjacent fault strands. We plan to present final results at the SCEC 2016 annual meeting, and write-up these results for publication in Fall, 2016.
Intellectual Merit This project applies a recent technique for dating mid-late Quaternary (1,000,000 – 100,000 y.b.p.) surfaces in southern California. These surfaces are omnipresent along the southern San Andreas Fault, but our inability to accurately date them has hindered interpretation of long-term slip rates along the San Andreas and other faults. Isochron burial dating with in situ cosmogenic 10Be and 26Al has been used for the last several years, but recent advances in AMS at PRIME Lab enable dramatic improvement in detection limits, potentially pushing the lower age limits of the method to well below 100 ka. Our new, 26Al/10Be burial ages from buried paleosols will provide invaluable geochronology from uplifted markers along the fault, and provide new, long-term slip rates that can be used for geophysical models and improve our understanding of the rupture history of these fault zones.
Broader Impacts This project has involved 1 MS student and 4 undergraduates from California State University Northridge. Travel support from this project allowed CSUN MS student Brittany Huerta to stay in the Coachella Valley for one month. Brittany is the first in her family to graduate college or go to graduate school, and she has thrived on the opportunity to focus on field work supported from this project. Moreover, this project has created a new collaboration between CSU Northridge, Purdue University, and the USGS that will continue for many years.
Exemplary Figure Figure 1. Digital elevation model of Whitewater Hill, showing the locations of two buried paleosols and the locations of the sample sites. Figure modified from Brittany Huerta.