Holocene geologic slip rate for the Banning strand of the southern San Andreas Fault, southern California

Journal of Geophysical Research B: Solid Earth
By: , and 

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Abstract

Northwest directed slip from the southern San Andreas Fault is transferred to the Mission Creek, Banning, and Garnet Hill fault strands in the northwestern Coachella Valley. How slip is partitioned between these three faults is critical to southern California seismic hazard estimates but is poorly understood. In this paper, we report the first slip rate measured for the Banning fault strand. We constrain the depositional age of an alluvial fan offset 25 ± 5 m from its source by the Banning strand to between 5.1 ± 0.4 ka (95% confidence interval (CI)) and 6.4 + 3.7/−2.1 ka (95% CI) using U-series dating of pedogenic carbonate clast coatings and 10Be cosmogenic nuclide exposure dating of surface clasts. We calculate a Holocene geologic slip rate for the Banning strand of 3.9 + 2.3/−1.6 mm/yr (median, 95% CI) to 4.9 + 1.0/−0.9 mm/yr (median, 95% CI). This rate represents only 25–35% of the total slip accommodated by this section of the southern San Andreas Fault, suggesting a model in which slip is less concentrated on the Banning strand than previously thought. In rejecting the possibility that the Banning strand is the dominant structure, our results highlight an even greater need for slip rate and paleoseismic measurements along faults in the northwestern Coachella Valley in order to test the validity of current earthquake hazard models. In addition, our comparison of ages measured with U-series and 10Be exposure dating demonstrates the importance of using multiple geochronometers when estimating the depositional age of alluvial landforms.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Holocene geologic slip rate for the Banning strand of the southern San Andreas Fault, southern California
Series title Journal of Geophysical Research B: Solid Earth
DOI 10.1002/2015JB012004
Volume 120
Issue 8
Year Published 2015
Language English
Publisher American Geophysical Union
Publisher location Richmond, VA
Contributing office(s) Earthquake Science Center
Description 25 p.
First page 5639
Last page 5663
Online Only (Y/N) N
Additional Online Files (Y/N) N