Latest Pleistocene and Holocene Slip Rate for the San Bernardino Strand of the San Andreas Fault, Plunge Creek Southern California: Implications for Strain Partitioning within the Southern San Andreas Fault System for the last 32 ka

Sally F. McGill, Lewis A. Owen, Ray J. Weldon, & Katherine J. Kendrick

Published October 2, 2012, SCEC Contribution #1596

An alluvial succession on the northeast side of the San Bernardino strand of the San Andreas Fault includes distinctive aggradational and degradational features that can be matched with correlative features on the southwest side of the fault. Key among these are (a) a terrace riser on the northeast side of the fault that correlates with an offset channel wall on the southwest side of the fault and forms a basis for slip estimates for the period 32 ka to the present, and (b) a small alluvial fan on the southwest side of the fault that has been matched with its most likely source gullies on the northeast side of the fault and forms a basis for slip estimates for the last 10 ka. Slip estimates for these two separate intervals are nearly identical—12.7 (+5.5, -4.4) mm/yr for the older episode and 11.5 ± 2.3 mm/yr for the younger.

These rates are only half the previously published slip rate for the San Andreas Fault to the northwest in Cajon Pass, a rate that traditionally is extrapolated southeastward along the San Bernardino section of the fault. Results from Plunge Creek suggest that about half of the 25 mm/yr rate at Cajon Pass transfers southeastward to the San Jacinto Fault, as proposed by other workers on the basis of regional geologic relations. At the same time, the latest Pleistocene and Holocene slip rate at Plunge Creek is twice that of rates inferred for the San Bernardino section of the San Andreas Fault based on elastic block modeling of geodetic data.

Citation
McGill, S. F., Owen, L. A., Weldon, R. J., & Kendrick, K. J. (2012). Latest Pleistocene and Holocene Slip Rate for the San Bernardino Strand of the San Andreas Fault, Plunge Creek Southern California: Implications for Strain Partitioning within the Southern San Andreas Fault System for the last 32 ka. Geological Society of America Bulletin, 125(1-2), 48-72. doi: 10.1130/B30647.1.