Recently a "major fault zone," the "North Channel Slope fault" was mapped along the northern margin of the Santa Barbara basin by U.S. Geological Survey personnel. The fault consists of a steep topographic escarpment (the north channel slope) and two well-documented faults to the east and west. By connecting the Pitas Point fault, the escarpment, and the F-1 (or Point Conception) fault to the west, a major zone over 100 km (62 mi) in length was postulated. Unfortunately, the connection and the continuous zone are nonexistent.

We have reviewed over 100 deep penetration to high resolution seismic reflection profiles along the escarpment between the Point Conception fault and Coal Oil Point--a distance of 50 km (31 mi). No through-going fault zone is present. Several small, discontinuous faults are mapped, such as the faulting south of the Molino anticlinal fold. But continuous, unbroken, late Neogene and Quaternary reflectors separate such minor high-angle reverse faults. Our interpretation of the deep structure along the margin is in agreement with that of the industry; there is no through-going fault zone.

Rather than connecting with the "steep escarpment," the Pitas Point fault appears to die out south of the Hondo anticlinal structure and cannot be traced beneath the Conception submarine fan to the west. In this area, the fault is expressed as a series of steeply south-dipping, monoclinal flexures.

The F-1 or Point Conception fault dies out immediately west of Gaviota. From this point westward to Point Conception, it is a north-dipping (65°±), high-angle reverse system that is composed of three en echelon segments with total length of approximately 20 km (12.5 mi) but less than 25 km (15.5 mi). Holocene activity along the eastern and western fault segments is documented by the disruption of the Holocene shelf surface and the distribution of Holocene sediment veneer. The surface over the fault zone is bowed about 3 m (10 ft), and the estimated maximum rate of uplift is 0.3 mm/yr.

The South Santa Ynez fault extends offshore southwestward from Gaviota. The fault is cut by the Point Conception fault near the shelf break. Beyond the edge of the shelf, the South Santa Ynez fault is located south of the Point Conception fault, and represents a north-dipping, high(?)-angle reverse fault. The latest displacements appear to be mid-late(?) Quaternary. The western part of the fault, which underlies the Conception fan, is poorly defined.

A review of the earthquake activity (1932-1981) of the northwestern Santa Barbara Channel region shows several scattered epicenters with magnitude range of 3.0 to 4.5. The fault plane solution for the October 1, 1959 (M = 4.5), event indicates right-lateral strike-slip faulting along a north-south direction with northeast-southwest compressive stress. No major historical earthquakes (1800-1932) have occurred in this region, nor is there a trend of epicenters along the north channel slope.

In summary, the existence of a "North Channel Slope fault zone" is not supported by the available evidence.

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