Document Type


Date of Original Version





The San Clemente fault, located in the California Continental Borderland, is an active, northwest trending, right‐lateral, wrench fault. Sea Beam data are used to map the major tectonic landforms associated with active submarine faulting in detail unavailable using conventional echo‐sounding or seismic reflection data. In the area between North San Clemente Basin and Fortymile Bank, the major late Cenozoic faults are delineated by alignments of numerous tectonic landforms, including scarps, linear trenches, benches, and sags. Character and spatial patterns of these landforms are consistent with dextral wrench faulting, although vertical offsets may be substantial locally. The main trace of the San Clemente fault cuts a straight path directly across the rugged topography of the region, evidence of a steeply dipping fault surface. Basins or sags located at each right step in the en echelon pattern of faults are manifestations of pull‐apart basin development in a right‐slip fault zone. Seismic reflection profiles show offset reflectors and a graben in late Quaternary turbidites of the Navy Fan, where the fault zone follows a more northerly trend. Modern tectonic activity along the San Clemente fault zone is demonstrated by numerous earthquakes with epicenters located along the fault's trend. The average strike of the San Clemente fault is parallel to the predicted Pacific‐North American relative plate motion vector at this location. Therefore we conclude that the San Clemente fault zone is a part of the broad Pacific‐North American transform plate boundary and that the southern California region may be considered as a broad shear zone.