STRUCTURE OF THE SAN FERNANDO BASIN, CALIFORNIA, BASED ON ANALYSIS OF GRAVITY AND MAGNETIC DATA
Gravity and magnetic data clearly image other major basin-bounding structures. Magnetic data suggest a major magnetic terrane boundary at or near the Verdugo fault, the eastern margin of the basin. The Verdugo fault may dip to the southwest along its southern part and therefore have a normal fault geometry (or a stack of several thrust faults stepping away from the mountain front). The northern segment of the Verdugo fault produces gravity and magnetic anomalies clearly indicative of a northeast-dipping thrust fault geometry. Gravity data suggest that the western margin of the basin is linear and strikes about N45E. The northeast-trending gravity gradient follows part of the 1971 San Fernando aftershock distribution called the Chatsworth trend. The aftershocks of the 1994 Northridge earthquake also appear to follow this northeast-trending gravity gradient as it bends into alignment with the east-west-trending gravity gradients associated with the Ventura basin margins.