COMPRESSION DIRECTIONS NORTH OF THE SAN FERNANDO VALLEY DETERMINED FROM BOREHOLE BREAKOUTS

摘要

Borehole breakouts in 4 nearly vertical oil wells, and several other deviated holes, in the San Fernando Valley and Santa Susana Mountains suggest a maximum horizontal compressive stress direction (S-H) of N49 degrees W. These wells provide information about the stress field from 1974 to 1983 in the uppermost crust (< 3 km depth) near the aftershock zones of the January 1994 Northridge earthquake and the February 1971 Sylmar earthquake. This direction of S-H is anomalous with respect to the N to NNE directions of S-H Seen in other regional data, but is consistent with the structural complexity of this zone, including local changes in strike of major thrust fault zones and the presence of lateral ramps in both the Santa Susana and San Fernando faults. [References: 20]