SCEC Award Number 14125 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title How and when do faults get hot? Surface chemistry and geochronological investigations of seismic slip
Investigator(s)
Name Organization
James Evans Utah State University Alexis Ault University of Arizona
Other Participants 1 graduate student; 1 SCEC intern; Dr. Peter Reiners of U Arizona lab
SCEC Priorities 3b, 3c, 4a SCEC Groups FARM, SDOT, EFP
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 We have developed a new fault surface paleothermometer that exploits the temperature-sensitive oxidation state changes in transition metals that are a result of shear heating during seismic slip (Evans et al., 2014). We use transition metal surface chemistry to document iron and Mn oxidation state changes and determine the peak temperatures attained during slip on faults coated by Fe-oxides. We (Ault et al., 2014; submitted) have also developed methods to directly date the slip on faults using U-Th/He geochronology. With these methods, we are dating several faults of the San Andreas fault, exhumed in the Mecca Hills, and determining the likely peak temperatures of faults of the West Salton Detachment Fault, faults of the Elsinore fault, and the San Andreas fault. Currently we have examined with optical and scanning electron microscopy the texture of the faults, and isolated 10 samples for U-Th/He dating. We are waiting for time at the University of Utah X-Ray Photoelectric Spectrographic lab, and the Stanford Linear Accelerator lab XANES lab to determine peak temperatures.
Intellectual Merit This work focuses on two key topics of key interest for fault zone analyses: What are the peak temperatures of fault slip, and when did faults slip? Our work addresses both of these topics directly; peak temperatures are a key data set to determine the dynamic friction processes and coefficients for faults. Dating faults by dating the fault surfaces directly is also an important topic; rather than rely on just the cross cutting relationships, we hope to develop a means to determine when individual faults slipped.
Broader Impacts This worked supports Amy Moser, an MSc student at USU; and partially support Kelly Bradbury, Phd Researcher at USU. This work is also used in our general geology presentations to community groups and was highlighted in a USU -wide lecture in April, 2015. . Moser, Bradbury, Evans, and field assistant Simona Clausnitzer answered a range of questions and gave impromptu talks ranging from 5 to 20 minutes in length on topics such as the tectonic, rock, and seismic cycles; the San Andreas fault and seismic hazards; southern California geology; rock mechanics; seismology; and the nature of the SCEC program. We estimate having substantive discussions with ~ 50 people in January and February.
Exemplary Figure Figure 1. Field photos and preliminary analyses of iron-oxide coated slip surfaces of the Mecca Hills, Southern California. (A) Field photo of iron-oxide slip surface in Precambrian/Mesozoic metamorphic basement rock. (B) Scanning electron microscope (SEM) image of a similar iron-oxide slip surface from the Mecca Hills showing slickenline lineations. (C) Same SEM image showing qualitative elemental chemistry of the slip surface using energy-dispersive X-ray spectroscopy (EDS). Elemental iron was the second most abundant after oxygen.