Segmentation and Thrusting Along the Offshore Newport-Inglewood-Rose Canyon Zone of Deformation

Abstract

The offshore Newport-Inglewood-Rose Canyon (NI-RC) zone of deformation is a 106-km-long, linear zone of folds and faults that extend from Newport Beach to La Jolla. Using seismicity and high-resolution and digitally processed seismic reflection data, three distinct fault segments are defined. These segments control the position and trend of shelf break: (1) the Laguna Beach segment (Corona Del Mar to San Mateo Point), a right-stepping zone with activity decreasing southward to San Mateo Point, where the latest activity was middle Holocene. (2) The San Onofre segment (San Mateo Point to Oceanside), where a major, 2-km-wide, left-stepping break occurs near the center of this segment opposite San Onofre; it is associated with an apparent basement discontinuity, a major blind thrust ramp and bowing of the continental slope. Shoreward of the NI-RC zone a 20-km-long synclinal fold trends subparallel to the zone. (3) The La Jolla segment (Oceanside to La Jolla), north of Encinitas, overlapping, left-stepping fault splays are associated with folding and thrusting. Preliminary earthquake focal mechanism studies suggest that right-lateral faulting, with a minor reverse component, is dominant along the NI-RC Zone. Earthquake foci do not seem to be related to the thrust faults. Compressional deformation along the zone ismore » thought to be a direct result of relative North American/Pacific plate motion direction changes at 4 Ma. Deformation was concentrated near the left-stepping break in the San Onofre segment, perhaps producing a detached block or flake. Mapped structures suggest the NI-RC is dislocated by the blind' thrust ramp.« less