North Channel Slope Fault, Santa Barbara Basin, California: A Reevaluation: ABSTRACT

Abstract

Recently a zone, the North Channel Slope fault was mapped along the northern margin of the Santa Barbara basin by U.S. Geological Survey personnel. The consists of a topographic escarpment (the north channel slope) and two well-documented faults to the east and west. By connecting the Pitas Point fault, the and the F-1 (or Point Conception) to the west, a major over 100 km (62 mi) in length was postulated. Unfortunately, the connection and the continuous are nonexistent. We have reviewed over 100 deep penetration to high resolution seismic reflection profiles along the escarpment between the Point Conception and Coal Oil Point--a distance of 50 km (31 mi). No through-going 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 zone. Rather than connecting with the steep escarpment, the Pitas Point 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 is expressed as a series of steeply south-dipping, monoclinal flexures. The F-1 or Point Conception 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 segments is documented by the disruption of the Holocene shelf surface and the distribution of Holocene sediment veneer. The surface over the is bowed about 3 m (10 ft), and the estimated maximum rate of uplift is 0.3 mm/yr. The South Santa Ynez extends offshore southwestward from Gaviota. The is cut by the Point Conception near the shelf break. Beyond the edge of the shelf, the South Santa Ynez 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 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 zone is not supported by the available evidence. End_of_Article - Last_Page 461------------