February 9, 1971 – Southern California

Posted by cdj On February - 10 - 2012

Forty-one years ago, on February 9, 1971 at 6:01 AM (PST) the destructive San Fernando (Sylmar) California earthquake (M=6.6) occurred, centered in an area of the San Gabriel Mountains near San Fernando. Strong ground shaking lasted about 60 seconds but resulted in property damage estimated at $505 million (1971$), over 2,000 personal injuries and 65 deaths. The USGS reported that surface faulting, which extended roughly east-west for about 15 kilometers, provided a maximum vertical offset measured on a single scarp of about 1 meter, the maximum lateral offset about 1 meter, and the maximum shortening (thrust component) about 0.9 meters. Shaking resulted in dramatic damage at the Olive View and Veterans Administration Hospitals and the collapse of new freeway overpasses. Many older buildings, often of unreinforced masonry construction, in the Alhambra, Beverly Hills, Burbank, and Glendale areas were damaged beyond repair. Water, gas, sewer, and electrical utilities of all kinds were damaged, both above and below ground. Severe ground fracturing and landslides caused extensive damage in areas where faulting was not observed, notably in the Upper Lake area of Van Norman Lakes. Two dams, the Lower Van Norman Dam and the Pacoima Dam, were damaged severely. The severity of the damage near a heavily populated region of the contiguous United States spurred California Governor Reagan’s administration to expand government responsibility in earthquake response and hazard mitigation with some urgency which created a new era in earthquake engineering in the U.S..

As a result, the Alquist-Priolo Earthquake Fault Zoning Act was signed into California law on December 22, 1972 to mitigate the hazard of surface faulting to structures for human occupancy. The devastation caused by the 1971 Sylmar earthquake propelled the California Legislature to pass the Alfred E. Alquist Hospital Seismic Safety Act that requires that acute care hospitals in California be designed and
constructed to withstand a major earthquake and remain operational immediately after an earthquake. Multilateral processes for declaring local, regional and federal disasters were reviewed. In 1975, passage of the Seismic Safety Act established the Seismic Safety Commission to advise the Governor, Legislature, and state and local governments on ways to reduce earthquake risk in California. After the earthquake the California Department of Transportation (CALTrans) instituted an ambitious program of highway bridge retrofits with public overview and evaluation (e.g.: “The Race to Seismic Safety” (Dec. 2003)).

Federally, following extensive scientific investigation lead by United States Geological Survey, the U.S. Congress established the National Earthquake Hazards Reduction Program (NEHRP) when it passed the Earthquake Hazards Reduction Act of 1977, Public Law (PL) 95–124. Congress’ stated purpose for NEHRP was “to reduce the risks of life and property from future earthquakes in the United States through the establishment and maintenance of an effective earthquake hazards reduction program.” NEHRP’s scope recognized that earthquake-related losses could be reduced through improved design and construction methods and practices, land use controls and redevelopment, prediction techniques and early-warning systems, coordinated emergency preparedness plans, and public education and involvement programs.

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