![]() Geological Survey, made research and policy recommendations that in part contributed to the City of Los Angeles enacting an ordinance in 2015 to retrofit weaker first-story wood-frame buildings and non-ductile, or brittle, concrete buildings, which are both more vulnerable to collapse during strong shaking. Over the years, NEHRP agencies, including the Federal Emergency Management Agency (FEMA), the National Institute of Standards and Technology, the National Science Foundation and the U.S. Congress eventually passed the Earthquake Hazards Reduction Act of 1977, which led to the National Earthquake Hazards Reduction Program, or NEHRP, and was pivotal in helping establish what is now the USGS Earthquake Hazards Program. On the federal level, Congress renewed its interest in earthquake safety, held hearings and introduced new bills to establish a national earthquake research program. It prompted Governor Ronald Reagan to declare Los Angeles County a disaster area and President Richard Nixon to send Vice President Spiro Agnew to inspect the area.Īfter the San Fernando earthquake, the State of California enacted the Alquist Priolo Act to limit construction along faults that likely caused earthquakes able to rupture the ground surface in the last 11,000 years. It led to 64 deaths and more than $500 million in damage. The 1971 San Fernando, or Sylmar, earthquake was the worst to hit an urban area of California since the 1933 magnitude-6.4 Long Beach quake. ![]() Approximately 80,000 people did evacuate as officials lowered the water levels in the dam. ![]() ![]() “As wind-whipped waves chewed at the damaged lip of the 1,100-foot Van Norman Dam, police spread through a nine-square-mile area between the reservoir and the Ventura Freeway, warning residents to evacuate,” The Los Angeles Times reported on February 10, 1971. The Lower Van Norman Dam, which sat above the San Fernando Valley in Los Angeles County, had nearly collapsed in the wake of the quake. “It was hard to believe what I saw,” he said. After checking on his wife and child, he drove to the top of the dam to examine the damage. A magnitude-6.6 earthquake was shaking his home nestled at the bottom of the dam. And then people waited.At 6 o’clock in the morning on February 9, 1971, the reservoir keeper of the Lower Van Norman Dam in Southern California tried to get out of bed. A dense network of instruments was installed in the hopes of trapping the earthquake, to detect precursory signs that might occur in seismic patterns, in ground movements, in electric or magnetic fields, in radon-gas emission, or in the chemistry or level of water wells. In 1985 a panel of 12 scientists, formally known as the National Earthquake Prediction Evaluation Council, endorsed a Parkfield prediction, saying that there was a 95 percent chance that a magnitude-6 earthquake would occur along the Parkfield section of the San Andreas Fault by 1993. All this gave credence to the idea that the next Parkfield earthquake might be predicted. Furthermore, an irrigation pipe that crossed the rupture zone separated nine hours before the 1966 event. The main shocks in 1934 and again in 1966 were preceded 17 minutes by a strong foreshock that was felt over a wide area. Moreover, there seemed to be definite precursory signs before the last two events. Each event has been nearly identical in size-corresponding to a magnitude-6 earthquake-and each successive event has occurred, on average, 22 years after the previous one. This 150-mile segment of the San Andreas Fault is distinctly different from the other parts of the fault: Here the fault is slowly and continuously sliding. So all of the San Andreas Fault has broken during a major earthquake in the last few hundred years except for a short middle segment that runs from San Juan Bautista to Cholame and includes the ranching community of Parkfield. The northern half of the southern segment-from Cholame to Cajon Pass-ruptured in 1857 the southern half of the southern segment-from San Gorgonio Pass to Bombay Beach-did so in about 1690. The southern segment begins around Cholame, just north of Carrizo Plain, and runs south, eventually forming the southern boundary of the Mojave Desert, continues through Cajon Pass and San Gorgonio Pass, can be picked up 20 miles east of Palm Springs in Coachella Valley, and ends at Bombay Beach on the east side of the Salton Sea. The northern segment runs from Cape Mendocino to San Juan Bautista-the part of the fault that ruptured in 1906. The San Andreas Fault can be divided into three main segments.
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