The Pacoima Dam Incident During the 1994 Northridge Earthquake

On January 17, 1994, the magnitude 6.7 Northridge earthquake struck the San Fernando Valley region of the City of Los Angeles. Pacoima Dam, a 365-foot-high concrete arch dam completed in February 1929 and located 11 miles southwest of the earthquake’s epicenter, experienced significant ground accelerations (over 1.7g near the top of the left abutment). The left abutment at the arch dam displaced 19 inches horizontally and 14 in. vertically during the event. The thrust block at the left abutment of the dam experienced a horizontal movement of 2.2 in. and a vertical displacement of 1.1 in. Some lift joints within the arch dam reportedly opened during the earthquake, and some of the 35 existing post-tensioned anchors at the left abutment (installed after the 1971 San Fernando earthquake) were damaged and required repairs.