SCEC Award Number 16057 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Holocene geologic slip rate for the Mission Creek Fault at the Three Palms Site in the Indio Hills
Investigator(s)
Name Organization
Whitney Behr University of Texas at Austin
Other Participants
SCEC Priorities 1a, 4a, 4b SCEC Groups Geodesy, Geology, SoSAFE
Report Due Date 03/15/2017 Date Report Submitted 05/22/2017
Project Abstract
 We have identified a new slip rate site at the southern end of the Mission Creek Fault between Pushawalla Canyon and Biskra Palms Oasis. At the Three Palms Site, three alluvial fans sourced from adjacent catchments have been displaced by the Mission Creek Fault. The central fan is best preserved and records a right lateral displacement of ~57 ± 3 meters. Uranium-series dating of pedogenic carbonate rinds constrain the minimum depositional age of this fan. A single sample from which 3 fractions were dated gave a model-independent isochron age of 3.3 +/- 0.6 ka, and the 5 oldest fractions gave a weighted mean age of 3.49 +/- 0.92 ka (95%CI). For comparison to the U-series, we also dated 14 samples using cosmogenic 10Be. The 10Be dataset yielded scattered ages ranging from 5.2-24.3 ka, and a mean age substantially older than the U-series of 13.6+12.0/-8.6 ka. Three 10Be ages cluster around 5.2 ka, and we interpret these to represent the maximum depositional age of the fan, with the rest of the 10Be ages recording variable amounts of inheritance. Combining the offset of 57 +/-3 and interpreted depositional age of 3.3-5.2 ka yields an estimated Holocene geologic slip rate of 10-22 mm/yr. This slip rate overlaps within error the late Pleistocene rates of 12-22 mm/yr at Biskra Palms to the east and is toward the lower end of the unpublished slip rate by Blisniuk et al. of 20-27 mm/yr measured west at Pushawalla Canyon.
Intellectual Merit Geologic slip rate data represent a primary input into earthquake hazard models for southern California. They also provide fundamental information about the constancy of seismic strain release, earthquake clustering, and fault loading mechanisms. Determining a Holocene slip rate for this section of the fault is critical for clarifying the total amount of southern San Andreas Fault slip transferred on to the Mission Creek Fault, and in turn for determining the proportion of southern San Andreas Fault slip that has been transferred to the Banning fault within the Indio Hills over Holocene timescales. In addition to obtaining slip rate data, we are testing the effectiveness of different cosmogenic sampling strategies and Quaternary geochronology techniques, which will be important to SCEC-related slip rate studies elsewhere.
Broader Impacts This research has thus far supported two students: a female undergraduate (Fryer) and a Hispanic M.S. student (Munoz). Fryer has conducted this work as her senior honors thesis at UT and had the opportunity to present at both SCEC and AGU and Munoz presented at SCEC in 2016 and will present at AGU this December. This work has also supported a female early career researcher (Behr). This research was also featured as part of a graduate-level Neotectonics course taught by PI Behr—the students in this course came to the Three Palms field area and learned about Quaternary mapping.
Exemplary Figure Figure 2 in full technical report.