Rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km. 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.  |  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 lasted technically for 12 seconds – it felt like a lot more than that! The earthquake caused over $500 million in damages, around 64 deaths, and critical destruction to the infrastructure of the region. A seismograph of the San Fernando earthquake in southern California in 1971 shows (top) ground acceleration, (center) velocity, and (bottom) displacement.  |  Today in Earthquake History, February 9, 2017  The 1971 San Fernando Earthquake. The San Fernando Fault, located 6 mi northwest of Burbank's downtown, caused the 6.6 magnitude 1971 San Fernando earthquake. The Olive View Medical Center was most adversely affected when a newly finished six story psychiatric ward collapsed, as well as the Veteran Administration Hospital in Sylmar. Geologists had known for a long time that the San Gabriel Mountains above the San Fernando Valley were riddled with faults. Mandatory Credit: Al Markado/ The Los Angeles Times/ ME.Quake71.2.1Ð22Ðm2.7.$. (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. Mandatory Credit: Brue Cox/ The L.A. Times/ ME.Quake71.1.1Ð22Ðm2.7.$. But it was generally accepted that none of these demarcation lines between two separate geologic units were active, meaning that they had not produced any earthquakes recently. 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. 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. LA Times staff writers: Kenneth Reich, 2/4/1996/ Los Angeles Daily News writer: Dana Bartholomew. 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. 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. 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. 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 San Fernando earthquake caused approximately 65 deaths, up to 1,000 personal injuries, and resulted in over 500 million dollars in damages. 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. In some areas it was offset more than 5 feet. Later, scientists at UCLA estimated that flooding following the collapse of the dam could have killed between 70,000 and 120,000 people.  |  The unreinforced concrete wings of the V.A Hospital, built in 1925, toppled leaving 47 dead and numerous victims trapped below the wreckage. 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. 1971 San Fernando earthquake map via USGS The M6.5 earthquake, also known as the Sylmar earthquake, killed 65 people and injured 2,000. 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. The San Fernando earthquake occurred in 1971 with a magnitude of 6.6. The southern California soil shook violently the morning of February 9, 1971. The San Fernando earthquake, 1971: Assessed at Richter magnitude 6.6, it …  |  Although the Richter magnitude of the tremblor was 6.6, … Following these to earthquakes, geologists are now sure that many more of these hidden faults crisscross deep beneath the San Fernando Valley. 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. Wikipedia article 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). Southern California The San Fernando Earthquake ofFebruary 9, 1971, offered a unique opportunity to assess many ofthe important scientific, engineering, and human concerns associated with earthquakes in a modern urban environment. The 1971 San Fernando earthquake, also known as the “Sylmar Quake,” took place on the morning of February 9, 1971 around 6:01am.  |  The 1971 San Fernando earthquake, also known as the “Sylmar Quake,” took place on the morning of February 9, 1971 around 6:01am. 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. Mandatory Credit: Al Markado/ The Los Angeles Times, Los Angeles Times Contributor: Larry Sharkey (retired), The Ground Beneath our Feet: A Hundred Years of Earthquakes in Los Angeles. It also occurred on a hitherto unknown fault, albeit a different one from the San Fernando fault (see Figure 2). Feb. 9, 1971, remains a big part of their lives, they said. Photo: E. Leyendecker, USGS. Old footage of some of the destruction resulting from the 1971 San Fernando earthquake. It is evident, however, that more faults in the San Fernando Valley area may be active today than are now recognized." The Ground Beneath our Feet: A Hundred Years of Earthquakes in Los Angeles. The question of whether it is wise to live below a dam behind which millions of acre feet of water are stored is usually rather low on people's lists of daily worries. 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. 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. 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). Damage from the 1971 quake. 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). 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). A little known fact was that the Van Norman … 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. 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. 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. 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. 1984 The slide carried away much of the crest and upstream concrete facing of the 2,100-foot-long dam. Objects under such forces would have been weightless for a few seconds, like astronauts in space. This earthen dam had partially liquefied and the top 30 feet of the edifice had crumbled. Earthquake hits the San Fernando Valley area of California. 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. It caused hospitals and schools to collapse, brought down sections of elevated freeways and cost 64 people their lives. The dam, which crumbled during the earthquake and during the following aftershocks, held approximately 3.6 billion gallons of water. 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 … 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. However, twenty-one years later the Newhall Pass Interchange would collapse again in almost the exact same location during the 1994 Northridge earthquake. Dam failure Even more surprising was the location of the focus of the quake, which later came to be known as the San Fernando earthquake. Categories:   The presence in California of major universities with strong and active earthquake research 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. LA Times staff writer: Kenneth Reich, 2/4/1996/ Los Angeles Daily News writer: Dana Bartholomew, 2/8/2016/ NBC Los Angeles writer: Jonathan Lloyd, 2/8/2019. 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. Such faults, which are unknown but can produce devastating quakes, are called blind thrust faults. During the Northridge earthquake in January 1994, more than 50 people were killed and the quake caused damage worth $35 billion. 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. 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 … The colored dots represent locations of the respective aftershocks of each quake. 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. Most dams are constructed well and they are built for eternity. My dad rushed us out and filmed some of the freeway damage. The San Fernando earthquake of February 9, 1971, was a geologic phenomenon not unlike many similar earthquakes that occur every year around the world. 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 … 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. Blind Thrust When seismologists checked their records they were utterly surprised. The event was one in a series that affected the Los Angeles area in the late … It is evident, however, that more faults in the San Fernando Valley area may be active today than are now recognized. Some of the most spectacular damage occurred at Olive View Hospital in Sylmar, California, where 49 people died despite its supposedly earthquake … 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 The Newhall Pass was rebuilt and finished in 1973 with the institution of new earthquake safety standards and additional steel rebar reinforcement. 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. It was the first strong quake to hit the area since the 1893 Pico Canyon quake, with an epicenter several miles west of Sylmar. More than once have dams failed or were overtopped due to the shaking of large earthquakes - with devastating consequences for the people living downstream. ", Figure 2: Earthquakes on two blind thrust faults caused severe damage in the San Fernando Valley. The 1971 earthquake was a massive disaster resulting in collapsed freeways, destroyed homes, and way too many ruined… But the threat of disaster didn't end when the shaking stopped. Earthquake Faults and Faulting On February 9th, 1971, at approximately 6:00am, the foothills of the San Gabriel Mountains were struck by a 6.7 earthquake. 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 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 unanticipated thrust earthquake had a magnitude of 6.5 on the Ms scale, and a maximum Mercalli intensity of XI (Extreme). The 1971 San Fernando earthquake (also known as the Sylmar earthquake) happened in the early morning of February 9 in the San Gabriel Mountains.It was at the northern edge of the San Fernando Valley in southern California.The quake measured 6.6 on the Richter scale.The damage was severe near the San Fernando Valley. The two blue lines mark the faults which ruptured in the San Fernando earthquake 46 years ago today. Earthquake Information Chronological Earthquake Index San Fernando Earthquake. 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. San Fernando earthquake Sylmar 6.6 Richter scale 1971 damage collapse building parking structure emergency temblor shake crack Major damage was concentrated at the Newhall Pass Interchange, which was under construction at the time of the 1971 San Fernando earthquake in Southern California. High Acceleration Yet, according to geologists, this disaster was only seconds away from being a really bad disaster to a historic catastrophic disaster. The 1971 earthquake was a massive disaster resulting in collapsed freeways, destroyed homes, and way too many ruined lives. (The earthquake of 9-Feb-1971). Never before had such a strong acceleration been recorded in an earthquake. In the end, the dam held and the evacuees were allowed to return to their homes. 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. Preparedness, Risks, and Hazards – and caused $553 million damage [in 1971 dollars, that would be about $3.28 billion in 2016 dollars]. The quake took place at 6 am under the town of Sylmar. United States Earthquakes, 1971 By Jerry L. Coffman and Carl A. von Hake Open-File report 84-971 Prepared in cooperation with National Oceanic and Atmospheric Administration, This report has not been reviewed for conformity with U.S. Geological Survey editorial standards.  |  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. 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