Pitas Point fault
Quaternary Slip and Geometry of the Red Mountain and Pitas Point-North Channel Faults, California

Marc J. Kamerling and Christopher C. Sorlien,

Institute for Crustal Studies, University of California, Santa Barbara, CA 93016

A structure contour map of an approximately 1.8 Ma horizon was created for onshore Ventura basin using existing cross sections based on surface geology and well data. This map was extended offshore into the eastern Santa Barbara Channel using industry seismic reflection data, well data, and sea floor geology. The N-dipping Pitas Point fault and the North Channel fault are interleaved or stacked along the same E-W trend, while the south branch of the offshore Red Mountain fault is a separate parallel structure 6 km to the north. Fault plane reflections from these faults were observed on 3D and 2-D seismic lines and faults were also detected by repeated sections and abrupt dip changes in wells. Shallow thrusts, folds, and south dipping reverse faults occur in the hanging wall and the footwall of the Pitas Point- North Channel fault. The Red Mountain fault splays into two main branches near the Carpinteria coast. The northern branch decreases in displacement to the west and continues as far west as offshore Goleta where it may die into folding. The south branch decreases in displacement to the west and dies out in a syncline south of Santa Barbara. Shortening across the Pitas Point-North Channel fault and hanging wall structures increases westward from near Pitas Point to a maximum south of Santa Barbara. Thus as displacement on the Red Mountain fault is decreasing westward the displacement on the Pitas Point-N. Channel fault is increasing. Displacement on one fault is compensating for the other. The Pitas Point and Red Mountain faults may merge with depth, detaching the intervening upper crustal block. Abrupt changes in shortening and fault-fold style along the strike of the Pitas Point-North Channel fault occur across NE-SW cross faults. Vertical axis block rotation of the segmented detached blocks can transfer slip from one fault to the other. Shortening of the 1.8 Ma horizon due to fault slip and folding across the Pitas Point-North Channel trend locally exceeds 5 km south of Santa Barbara, and exceeds 1 km across the south Branch of the Red Mountain fault south of Carpinteria. Ongoing unfolding and restoration of the digital map will allow slip, block rotation, and shortening to be quantified, and the structural-kinematic interpretation to be validated.

Kamerling, M. J., and Sorlien, C. C, 1999, Quaternary slip and geometry of the Red Mountain and Pitas Point-North Channel faults, California, Supplement to EOS, (Trans. AGU), v. 80, P. F1003