The slides in the San Fernando Dams during the earthquake of February 9, 1971

The February 9, 1971 earthquake in San Fernando Valley, California, caused slides in the embankments of two old adjacent hydraulic fill dams. At the 140-ft high Lower dam, the entire upstream face slid into the reservoir leaving only 5 ft of freeboard. At the 65-ft high Upper dam, the entire embankment from the waterline to the downstream toe moved downstream 6 ft, leaving a scarp just below the reservoir level on the upstream face. It is concluded that the slide in the Lower dam resulted from the development of an extensive zone of liquefaction near the base of the embankment. Some liquefaction is also believed to have occurred in the Upper dam; however, since a significant body of the sand in the upstream and downstream shells of this dam retained considerable strength, complete failure could not occur and the movements were limited in extent. Conclusions are presented concerning the applicability of analytical procedures for predicting the failure and movements that occurred.