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
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within error the late Pleistocene rates of 12-22 mm/yr at Biskra Palms to the east and is toward the lower end of the unpublished slip rate by Blisniuk et al.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.