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Detailed geologic investigations that included mapping, geomorphic analysis, drilling, and logging of natural and trench wall exposures were performed to characterize the Holocene behavior of the southeastern onshore reach of the San Simeon fault near San Simeon, California. Our field investigations revealed that the San Simeon fault consists of two and possibly four or more major strands that define a southeast-tapering zone that is about 400 m wide at Oak Knoll Creek, narrowing to about 120 m at San Simeon Cove, 2.6 km to the southeast. Geologic and soils data from four sites within this fault reach show that the primary San Simeon fault traces are northwest-trending, vertical to near-vertical, right-slip faults that have subhorizontal striae and slickensides. The ratio of strike slip to dip slip on primary traces is > 10:1 at the Borrow Pit site and about 8:1 to 10:1 at Airport Creek. These faults have undergone multiple slip events during the Holocene. We estimate a slip rate for the fault zone of 0.9 to 3.4 mm/yr, with a best constrained value of 1.0 to 1.4 mm/yr. Although our studies are confined to one major strand within the fault zone, analysis of deformed marine terrace strandlines suggests this estimate may closely approximate the value for the fault zone as a whole. Two fault strands, one at Oak Knoll Creek and the other at Airport Creek, yield net slip estimates of 1 to 2 m per event. Based on estimates of both slip rate and net slip per event, recurrence frequencies for the San Simeon fault are estimated to fall within the range of 265 to 2,000 yr, with best constrained values between approximately 600 and 1,800 yr. Evidence at Airport Creek suggests that slip events have not occurred at uniform intervals.

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