Bouguer gravity anomalies and magnetic anomalies off the Coast of Southern California

Abstract

Marine and land gravity measurements in the area bounded to the east and west by the 117°00′ and 120°00′ meridians and to the north and south by the 34°30′ and 32°30′ parallels of latitude have been compiled and a map of Bouguer anomalies drawn. A spatial filtering technique was used to separate the anomalies into short-, intermediate-, and long-wavelength components. The features outlined by the short-wave-length components show a pronounced NW-SE strike, and, wherever geologic or seismic evidence is available, there is an excellent correlation between the anomalies and geologic structures aligned parallel to the Coast Ranges. A greater continuity or alignment of these features is noticeable in the filtered anomalies than in the unprocessed gravity data or in the bathymetry. The pattern shown by the intermediate wavelengths has a pronounced east-west strike, parallel to the Transverse Ranges but extending far outside the Transverse Range province. There is a very abrupt transition between the oceanic crust of the Pacific Ocean and the intermediate borderland crust. The dip of the Mohorovicic discontinuity appears to exceed 45° beneath the continental slope. A map of total magnetic field anomalies in the offshore area has also been drawn. Two features have been interpreted in terms of intrusive masses which may be sources for the extensive volcanic rocks in the vicinity of Santa Barbara and San Clemente islands.