CHARACTER AND TIMING OF SLIP ON NORTHWEST-STRIKING FAULTS IN THE NORTHERN SANTA LUCIA RANGE, CENTRAL CALIFORNIA COAST

In the Central California Coast Ranges, relative plate motion not accounted for by the San Andreas fault is thought to be accommodated, in part, by right-lateral slip along other major strike slip faults of the San Andreas transform system such as the San Gregorio-Hosgri Fault Zone (SGHFZ) and the Rinconada Fault (RF), and by plate normal and/or oblique contraction. Late Pleistocene slip rates along the mostly offshore SGHFZ double from 1-2 mm/yr at San Simeon south of Monterey Bay, to 3-4 mm/yr at Ano Nuevo north of Monterey Bay, suggesting either an underestimation of slip rate at San Simeon or a transfer of slip to the SGHFZ between the two study sites. A possibility is that additional right-lateral slip is transferred westward from the RF through a broad zone of dextral shearing, including NW striking faults in the Northern Santa Lucia Range (NSLR) where the RF terminates after carrying 1-2 mm/yr of slip.

In this study, evidence of late Pleistocene and possibly younger dextral shear through the NSLR includes fault plane lineations on three exposures of the NW striking Tularcitos fault, oriented 20-60°SE, showing right-lateral components of slip. Previously unmapped NW striking, sub-vertical fault exposures located approximately 2 and 15 km northwest of the north end of the RF, contain fault plane lineation orientations of 10°SE and 31°SE respectively, indicating large right-lateral components of slip. These fault exposures offset late Pleistocene and possibly younger deposits. The presence of a fault and timing of offset at these locations is supported by geomorphic features indicative of dextral faulting that were identified on high-resolution satellite imagery along projected fault strikes. Holocene activity of Monterey Bay faults along with new kinematic data on the Tularcitos and unmapped faults suggest that dextral shearing occurred through the NSLR in the late Pleistocene or later.