Abstract: Seismicity and Tectonics of the Western Transverse Ranges: Ventura Basin Region to the San Fernando Valley

T. A. Jones, G. W. Simila

The microseismicity and associated fault plane solutions for the western Transverse Ranges is reviewed for 1983-1993. In Ventura

County, the San Cayetano fault, located north of the Santa Clara River basin, exhibits north-dipping reverse faulting. The Oakridge fault, located to the south in the Santa Clara River basin exhibits south-dipping reverse faulting. Recent hydrogeologic evidence in the Saticoy area of the Santa Paula water basin suggests that the Oakridge fault and an as yet unnamed associated fault may be acting as a groundwater barrier. Farther south, in the Ventura Basin, the Simi-Camarillo-Springville fault system also exhibits reverse fault motion. The April 1985 (M=4.0) event in the southern Ventura Basin indicated reverse motion at deep crustal depths as reported by Bryant and Jones (1989). Moving eastward to the north San Fernando Valley region, the Holser fault exhibits strike-slip motion. In ddition, the Santa Susana fault has north-dipping reverse motion, while microseismicity associated with the Northridge Hills fault shows a combination of steeply north-dipping and strike-slip faulting. Generally, focal mechanisms in the western Transverse Ranges reflect a north-south compressive stress, which may produce possible crustal detachment structures.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994