Abstract: Constraints on the Rate of N-S Convergence in the Venture Area of the Western Transverse Ranges Based on Strike-Slip Fault Rates in Southern and Baja California West of the San Jacinto Fault
T. K. Rockwell
The rate of north-south convergence in the Ventura area of the western Transverse Ranges can be no higher than the combined rate of northwest-striking dextral faults west of the San Jacinto and San Andreas faults in southern and Baja California. The principal contributors include the Elsinore-Whittier fault zone and the Newport-Inglewood-Rose Canyon, Coronado Bank-Palos Verdes, San Diego Trough-San Pedro basin, and San Clemente fault zones of the inner continental borderland. Recent studies along the Elsinore fault zone demonstrate a Holocene dextral slip rate of 4 to 5 mm/yr, over half of which is accommodated by brittle slip along the Whittier fault in the Los Angeles basin. The inner continental borderland faults collectively distribute about 5 mm/yr of dextral slip based on the la e Quaternary rate determined for the Agua Blanca fault in northern Baja California, which directly transfers slip to the San Diego Trough and Coronado Bank faults. Over half of this deformation is apparently accommodated by the Palos Verdes fault in the Los Angeles basin. The seismically active San Miguel fault zone in northern Baja California is now known to contribute less than 0.5 mm/yr of dextral slip. Only the slip rate on the San Clemente fault is unconstrained in that at least part of its activity transfers from offshore faults south of the Agua Blanca fault zone in Baja California. Slip from this fault, however, probably does not contribute to convergence in the Ventura region due to its westerly position and strike.
The above data suggest that the rate of shortening in the Ventura region should not exceed about 10 mm/yr, in close agreement to recent geodetic measurements. Reevaluation of folding of late Quaternary terraces along the Ventura River generally support this rate and indicate that most of the active convergence is accommodated by structures underlying the Ventura Avenue anticline. In the central Ventura basin, about 75% of the surface shortening is accommodated by the San Cayetano and Oak Ridge faults, with the balance accommodated by structures to the south of the basin, including the Santa Monica fault zone.
AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994