Never before had such a strong acceleration been recorded in an earthquake. In some areas it was offset more than 5 feet. The 1971 San Fernando earthquake, also known as Sylmar earthquake, struck the San Fernando Valley near Sylmar at 6:00:55 a.m. PST on February 9, 1971, with a magnitude of 6.6. The colored dots represent locations of the respective aftershocks of each quake. 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. The Newhall Pass was rebuilt and finished in 1973 with the institution of new earthquake safety standards and additional steel rebar reinforcement.  |  Southern California Following the San Fernando Earthquake, new seismic safety building codes and legislation such as the Alquist-Priolo Act, which bans development near active fault lines in California, were put into place. (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. 1971 San Fernando earthquake map via USGS The M6.5 earthquake, also known as the Sylmar earthquake, killed 65 people and injured 2,000. My dad rushed us out and filmed some of the freeway damage. The quake lasted technically for 12 seconds – it felt like a lot more than that! The slide carried away much of the crest and upstream concrete facing of the 2,100-foot-long dam. Some of the most spectacular damage occurred at Olive View Hospital in Sylmar, California, where 49 people died despite its supposedly earthquake … Following these to earthquakes, geologists are now sure that many more of these hidden faults crisscross deep beneath the San Fernando Valley. Burbank, California - Wikipedia In the 1971 San Fernando earthquake, which took place along the western edge of the Sierra Madre Fault, surface ruptures were nearly 12 mi long, including one portion a few miles northwest of Glendale. Yet, according to geologists, this disaster was only seconds away from being a really bad disaster to a historic catastrophic disaster. 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. The San Fernando earthquake occurred in 1971 with a magnitude of 6.6. It is postulated that the initial event took place at depth on the Sierra Madre fault zone which runs along the base of the San Gabriel Mountains. In some areas of the epicentral region the ground had shaken so violently that seismic sensors recorded accelerations of more than 1.25 g, where g is the standard gravitational acceleration at the Earth's surface.  |  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 Newhall Pass infrastructure project which is located northwest of the San Fernando Valley in Weldon Canyon and less than eight miles from two other major freeway interchanges, prompted Councilman Donald Lorenzen to criticize conglomeration of freeways and connectors as “putting too many eggs in one basket.” The majority of damage to freeway structures during the “Sylmar Quake” ranged from minor cracking and slanting to the complete destruction of major sections of the interchange bridges. On Feb. 9, 1971, the deadly San Fernando Earthquake rattled Southern California, leaving more than 60 people dead and causing more than $500 million in property damage. The unreinforced concrete wings of the V.A Hospital, built in 1925, toppled leaving 47 dead and numerous victims trapped below the wreckage. LA Times staff writers: Kenneth Reich, 2/4/1996/ Los Angeles Daily News writer: Dana Bartholomew. 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 quake took place at 6 am under the town of Sylmar. ", Figure 2: Earthquakes on two blind thrust faults caused severe damage in the San Fernando Valley. But when seismologists checked the epicentral area they realized that for about 6 miles a fault along the foothills of the San Gabriels had broken through the surface during the quake. – and caused $553 million damage [in 1971 dollars, that would be about $3.28 billion in 2016 dollars]. Damage from the 1971 quake. 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. Once the shaking was over and rescuers started to assess the damage, the imminent fear of a new catastrophe arose: The Van Norman Dam just northwest of the town of San Fernando, where 3.6 billion gallons of drinking water were stored, was severely damaged. Although the Richter magnitude of the tremblor was 6.6, ranking it as moderate to large, but not great, it shook a wide, heavily populated area, leaving death and destruction in its wake.  |  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. The unanticipated thrust earthquake had a magnitude of 6.5 on the Ms scale, and a maximum Mercalli intensity of XI (Extreme). Categories:   The event was one in a series that affected the Los Angeles area in the late … 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. More chunks of earth collapsed with each new aftershock, reducing the height of the crown and bringing the water table dangerously close to the top of the dam (see Figure 1). A seismograph of the San Fernando earthquake in southern California in 1971 shows (top) ground acceleration, (center) velocity, and (bottom) displacement. It caused hospitals and schools to collapse, brought down sections of elevated freeways and cost 64 people their lives. 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. High Acceleration Wikipedia article The earthquake was the third major earthquake to occur in the state in 23 years (after the 1971 San Fernando Valley and 1989 San Francisco–Oakland earthquakes), the Northridge earthquake was the state's most destructive one since the San Francisco earthquake of 1906 and the one that cost the most expensive for reconstruction. The San Fernando earthquake caused approximately 65 deaths, up to 1,000 personal injuries, and resulted in over 500 million dollars in damages. 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. Rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km.  |  Around 80,000 residents were required to evacuate from the area for three days due to fears that the whole area would be flooded by the dam’s water reserve. Geologists had known for a long time that the San Gabriel Mountains above the San Fernando Valley were riddled with faults. In the end, the dam held and the evacuees were allowed to return to their homes. 1984 Mandatory Credit: Brue Cox/ The L.A. Times/ ME.Quake71.1.1Ð22Ðm2.7.$. The 1971 earthquake was a massive disaster resulting in collapsed freeways, destroyed homes, and way too many ruined lives. 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. 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. During the Northridge earthquake in January 1994, more than 50 people were killed and the quake caused damage worth $35 billion. 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.The unanticipated thrust earthquake had a moment magnitude of 6.5 or 6.7 (as determined by several independent institutions) and had a maximum Mercalli intensity of XI (Extreme). Bottom line: the 1971 Sylmar quake in Los Angeles produced the most destructive power of any earthquake in California since the Fort Tejon quake in 1857 (Richter 7.9). It is evident, however, that more faults in the San Fernando Valley area may be active today than are now recognized. 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. Seconds – it felt like a lot more than 5 feet later the Newhall Pass was rebuilt and finished 1973. Much of the focus of the region even more surprising was the location the... See Figure 2: Earthquakes on two blind thrust faults Mountains above the San Fernando Valley feet of the Hospital! 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