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

Peter O. Gold, Whitney M. Behr, Dylan H. Rood, Warren D. Sharp, Thomas K. Rockwell, Katherine J. Kendrick, & Aaron Salin

Published August 18, 2015, SCEC Contribution #2083

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% C.I.) and 6.4 +3.7/-2.1 ka (95% C.I.) using U-Th 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% C.I.) to 4.9 +1.0/-0.9 mm/yr (median, 95% C.I.). This rate represents only 20-30% of the total slip accommodated by this section of the southern San Andreas Fault, suggesting a model in which slip may be more evenly partitioned between the Mission Creek, Banning and Garnet Hill strands 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.

Key Words
Banning fault strand, southern San Andreas Fault, slip rate, earthquake hazard, U series pedogenic carbonate

Citation
Gold, P. O., Behr, W. M., Rood, D. H., Sharp, W. D., Rockwell, T. K., Kendrick, K. J., & Salin, A. (2015). Holocene geologic slip rate for the Banning strand of the southern San Andreas Fault, southern California. Journal of Geophysical Research: Solid Earth, 120(8), 5639-5663. doi: 10.1002/2015JB012004. http://onlinelibrary.wiley.com/doi/10.1002/2015JB012004/full

Related Projects & Working Groups
Southern San Andreas Fault Evaluation, Working Group on California Earthquake Probabilities