Seismological Overview of the 1994 Northridge Earthquake Sequence in California

Egill Hauksson

Published 1995, SCEC Contribution #180

The Northridge earthquake occurred on January 17,1994 at 4:30 am. Pacific Standard Time in the San Fernando Valley. The hypocenter was about 32 km west-northwest of Los Angeles at a relatively deep focal depth of 19 km. The moment magnitude for the Northridge earthquake is Mw 6. 7. The 1994 Northridge earthquake occurred on a south-southwest dipping thrust ramp beneath the San Fernando Valley and thus reemphasized the seismic hazard of concealed faults in the greater Los Angeles region. The occurrence of the Northridge earthquake also shows that this high rate of seismicity along the northern edge of the Los Angeles basin is continuing. The mainshock was followed by an energetic aftershock sequence. Eight aftershocks of M 5.0 and 48 aftershocks of 4 M<5 occurred between January 17 and September 30,1994. The aftershocks extend over most of the western San Fernando Valley and Santa Susana Mountains. The 1971 San Fernando and the 1994 Northridge earthquakes ruptured partially abutting fault surfaces on opposite sides of a ridge. Both earthquakes accommodated north-south contractional deformation of the Transverse Ranges.

Hauksson, E. (1995). Seismological Overview of the 1994 Northridge Earthquake Sequence in California. In Hauksson, E., & (Eds.), California Division of Mines and Geology, Special Volume, (, pp. 17-38) , :