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

Borehole breakouts in 4 nearly vertical oil wells, and several other d eviated holes, in the San Fernando Valley and Santa Susana Mountains s uggest 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 aftershoc k zones of the January 1994 Northridge earthquake and the February 197 1 Sylmar earthquake. This direction of S-H is anomalous with respect t o the N to NNE directions of S-H Seen in other regional data, but is c onsistent with the structural complexity of this zone, including local changes in strike of major thrust fault zones and the presence of lat eral ramps in both the Santa Susana and San Fernando faults.