That’s because a fault with the provocative name of the Santa Susana thrust exhibited a lot of movement that day, with the result being an earthquake … – and caused $553 million damage [in 1971 dollars, that would be about $3.28 billion in 2016 dollars]. Objects under such forces would have been weightless for a few seconds, like astronauts in space. However, when you live in earthquake country, you might want to give the question a second thought. Old footage of some of the destruction resulting from the 1971 San Fernando earthquake. But at 42 seconds after 6 a.m. on a Tuesday morning 25 years ago this week, Feb. 9, 1971, the Sylmar-San Fernando earthquake hit the Valley and … However, twenty-one years later the Newhall Pass Interchange would collapse again in almost the exact same location during the 1994 Northridge earthquake. Evidence is presented which suggest that the 1971 San Fernando earthquake may have been a double event that occurred on two separate, subparallel thrust faults. Mandatory Credit: Brue Cox/ The L.A. Times/ ME.Quake71.1.1Ð22Ðm2.7.$. More than 80,000 people living downstream had to leave their homes for four days, while engineers frantically shored up the dam and lowered the water level. Mandatory Credit: Al Markado/ The Los Angeles Times/ ME.Quake71.2.1Ð22Ðm2.7.$. Forty-six years ago today, the possibility of such a sudden dam burst was the hair-raising fear, in the chaos and devastation following the magnitude 6.7 earthquake that struck the San Fernando Valley north of Los Angeles. Yet, according to geologists, this disaster was only seconds away from being a really bad disaster to a historic catastrophic disaster. During the Northridge earthquake in January 1994, more than 50 people were killed and the quake caused damage worth $35 billion. Later known as the San Fernando Earthquake, the quake was responsible for $500 million dollars worth of damage and causes 65 deaths (most of the deaths occurred when the Veteran's Administration Hospital collapsed). The 1971 San Fernando Earthquake. The Ground Beneath our Feet: A Hundred Years of Earthquakes in Los Angeles. The San Fernando earthquake (also known as the Sylmar earthquake) was a magnitude 6.6 earthquake that struck on February 9th, 1971 at 6:00 AM PST. The San Fernando earthquake of February 9, 1971, was a geologic phenomenon not unlike many similar earthquakes that occur every year around the world. Today in Earthquake History, February 9, 2017  The two geologists Carl Wentworth and Robert Yerkes from the US Geological Survey in Pasadena later wrote that "the San Fernando fault was discovered to be active only when it ruptured the ground surface on February 9, 1971. The 6.6 magnitude earthquake with an epicenter located along a 12 mile fault zone below the San Gabriel Mountains lasted approximately 12 seconds and affected the entire San Fernando Valley. The Newhall Pass was rebuilt and finished in 1973 with the institution of new earthquake safety standards and additional steel rebar reinforcement. The 1971 San Fernando-Sylmar earthquake, which measured 6.7 on the Richter scale of ground motion, occurred on a buried fault that was later named the Sierra Madre fault. The 1971 San Fernando earthquake shook loose a massive slide in the upstream slope of the Lower San Fernando Dam that lowered the crest about 30 feet. Following these to earthquakes, geologists are now sure that many more of these hidden faults crisscross deep beneath the San Fernando Valley. The Olive View Medical Center was most adversely affected when a newly finished six story psychiatric ward collapsed, as well as the Veteran Administration Hospital in Sylmar. The unanticipated thrust earthquake had a magnitude of 6.5 on the Ms scale, and a maximum Mercalli intensity of XI (Extreme). The 6.6 magnitude earthquake with an epicenter located along a 12 mile fault zone below the San Gabriel Mountains lasted approximately 12 seconds and affected the entire San Fernando Valley. The 1971 San Fernando earthquake, also known as the “Sylmar Quake,” took place on the morning of February 9, 1971 around 6:01am. The slide carried away much of the crest and upstream concrete facing of the 2,100-foot-long dam. It caused hospitals and schools to collapse, brought down sections of elevated freeways and cost 64 people their lives. Categories:   TYPE OF FAULTING: thrust TIME: February 9, 1971 / 6:01 am PST LOCATION: 34° 24.67' N, 118° 24.04' W MAGNITUDE: M W 6.5 DEPTH: 8.4 km FAULT INVOLVED: San Fernando fault zone; minor offset reported on the eastern Santa Susana fault zone But even now, after further detailed studies, they are not sure whether they have identified all blind faults in the area or if the valley's inhabitants are in for more surprises. Earthquake hits the San Fernando Valley area of California. The 1971 earthquake was a massive disaster resulting in collapsed freeways, destroyed homes, and way too many ruined lives. As the dam might collapse further and then be breached by the enormous pressure of the water behind it, authorities decided to evacuate an area of 10 square miles along the San Diego Freeway. Rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km. Teleseismic P, SV, and SH waves recorded by the WWSS and Canadian networks from the 1971 San Fernando, California earthquake (M L = 6.6) are modeled in the time domain to determine detailed features of the source as a prelude to studying the near and local field strong-motion observations. It was the first strong quake to hit the area since the 1893 Pico Canyon quake, with an epicenter several miles west of Sylmar. The 1971 San Fernando earthquake (also known as the Sylmar earthquake) occurred in the early morning of February 9 in the foothills of the San Gabriel Mountains in southern California. Some of the most spectacular damage occurred at Olive View Hospital in Sylmar, California, where 49 people died despite its supposedly earthquake … It also occurred on a hitherto unknown fault, albeit a different one from the San Fernando fault (see Figure 2). A seismograph of the San Fernando earthquake in southern California in 1971 shows (top) ground acceleration, (center) velocity, and (bottom) displacement. Figure 1: After the partial collapse of the Van Norman Dam in the San Fernando earthquake, the water came dangerously close to overtopping the dam. Within the southern California region alone, the historic record suggests that an earthquake of about this magnitude occurs on the average of once every four years ( Fig. Blind Thrust (hra135), Cooperative Institute for Deep Earth Research (CIDER), Northern California Earthquake Data Center (NCEDC), :  Destruction in the Eastern Aegean Sea, :  An Explosion in Beirut heard all over the Middle East, :  Quake in Turkey highlights the hazard in the East Bay. A little known fact was that the Van Norman … Source: USGS, How right they were was demonstrated 23 years later, when almost the same areas of the San Fernando Valley were again struck by a damaging earthquake. The San Fernando earthquake occurred in 1971 with a magnitude of 6.6. The 1971 San Fernando earthquake with a 6.6 magnitude and large aftershocks caused over $500 million in damages and destruction to infrastructure; including the collapsed freeway overpasses on the Interstate freeways 5, 14, and 210, destruction of several hospitals in the North Los Angeles area, and damage to the Van Norman Dam in Granada Hills. Preparedness, Risks, and Hazards the 1971 san fernando earthquake An hour before sunrise, at 6:01 AM, PST, on February 9, 1971, the San Fernando region was struck by one of the most devastating earthquakes in California history. (The earthquake of 9-Feb-1971). Such faults, which are unknown but can produce devastating quakes, are called blind thrust faults. This earthen dam had partially liquefied and the top 30 feet of the edifice had crumbled. 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