Onshore-offshore Cabrillo Fault, Palos Verdes, California: a Tectonic Fault Associated with the Palos Verdes Fault

John F. Schwiebert¹ and Robert D. Francis^2
110633 Tamarack Way, Stanton, CA 90680-2324
²Department of Geological Sciences, California State University, Long Beach

Our mapping shows that the Cabrillo fault (CF) is a steeply NE-dipping tectonic fault about 18 km in length on the Palos Verdes Peninsula and adjacent San Pedro Shelf. A previously proposed landslide origin for the fault is precluded by the fact that the fault continues offshore beyond the area proposed for the slide. The segment of the fault trace that is concave to the east, consistent with a landslide head scarp, is only about 4 km long. We have combined previous onshore mapping of the CF (based largely on geomorphic evidence), early 20^th century beach-cliff photography (correlated to GPS data using man-made reference points), intertidal outcrops, near-shore side scan sonar, offshore aerial photography, and offshore multibeam bathymetry (USGS) and seismic reflection data. These datasets provide a continuous map of this onshore-offshore fault trace, with a gap of only about 300 m at the shoreline, and with both terminations of the CF well delineated. The CF begins near the center of the Peninsula, about 1 km southeast of the oldest rock exposures (Mesozoic Catalina Schist) and strikes about S50E, sub-parallel to the Palos Verdes fault (PVF) to the east, and terminating or merging with the PVF adjacent to a short, 1.7 km releasing segment of the PVF about 11 km offshore. The CF runs more or less along the axis of the Palos Verdes anticlinorium, where it appears to truncate various Miocene and Pliocene units, as well as numerous fold axes. These and other features support a dominantly strike slip separation with a possible dip-slip component, which is similar to that documented for the PVF. This and the CF termination near the 1.7 km releasing PVF segment suggest that the two faults are closely related.

AAPG Search and Discovery Article #90076©2008 AAPG Pacific Section, Bakersfield, California