THE MAGNITUDE-6.7 NORTHRIDGE, CALIFORNIA, EARTHQUAKE OF 17-JANUARY-1994

The most costly American earthquake since 1906 struck Los Angeles on 1 7 January 1994. The magnitude 6.7 Northridge earthquake resulted from more than 3 meters of reverse slip on a 15-kilometer-long south-dippin g thrust fault that raised the Santa Susana mountains by as much as 70 centimeters. The fault appears to be truncated by the fault that brok e in the 1971 San Fernando earthquake at a depth of 8 kilometers. Of t hese two events, the Northridge earthquake caused many times more dama ge, primarily because its causative fault is directly under the city. Many types of structures were damaged, but the fracture of welds in st eel-frame buildings was the greatest surprise. The Northridge earthqua ke emphasizes the hazard posed to Los Angeles by concealed thrust faul ts and the potential for strong ground shaking in moderate earthquakes .