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. 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. Later, scientists at UCLA estimated that flooding following the collapse of the dam could have killed between 70,000 and 120,000 people. Damage from the 1971 quake. The unreinforced concrete wings of the V.A Hospital, built in 1925, toppled leaving 47 dead and numerous victims trapped below the wreckage. 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 1971 San Fernando earthquake, also known as the “Sylmar Quake,” took place on the morning of February 9, 1971 around 6:01am. Even more surprising was the location of the focus of the quake, which later came to be known as the San Fernando earthquake. It is evident, however, that more faults in the San Fernando Valley area may be active today than are now recognized." – and caused $553 million damage [in 1971 dollars, that would be about $3.28 billion in 2016 dollars]. Blind Thrust My dad rushed us out and filmed some of the freeway damage.  |  The quake took place at 6 am under the town of Sylmar.  |  The two blue lines mark the faults which ruptured in the San Fernando earthquake 46 years ago today. This earthen dam had partially liquefied and the top 30 feet of the edifice had crumbled. 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  Rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km. However, twenty-one years later the Newhall Pass Interchange would collapse again in almost the exact same location during the 1994 Northridge earthquake. The 1971 San Fernando earthquake, also known as the “Sylmar Quake,” took place on the morning of February 9, 1971 around 6:01am. The quake lasted technically for 12 seconds – it felt like a lot more than that! Preparedness, Risks, and Hazards Objects under such forces would have been weightless for a few seconds, like astronauts in space. 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. 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 … Old footage of some of the destruction resulting from the 1971 San Fernando earthquake. High Acceleration 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. Photo: E. Leyendecker, USGS. The presence in California of major universities with strong and active earthquake research Geologists had known for a long time that the San Gabriel Mountains above the San Fernando Valley were riddled with faults. 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. LA Times staff writers: Kenneth Reich, 2/4/1996/ Los Angeles Daily News writer: Dana Bartholomew. 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). It caused hospitals and schools to collapse, brought down sections of elevated freeways and cost 64 people their lives. 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). 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. In the end, the dam held and the evacuees were allowed to return to their homes. The 1971 earthquake was a massive disaster resulting in collapsed freeways, destroyed homes, and way too many ruined lives. 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. 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. 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. 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. 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. Earthquake Faults and Faulting 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 … 1971 San Fernando earthquake map via USGS The M6.5 earthquake, also known as the Sylmar earthquake, killed 65 people and injured 2,000. The unanticipated thrust earthquake had a magnitude of 6.5 on the Ms scale, and a maximum Mercalli intensity of XI (Extreme). Dam failure 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. In some areas it was offset more than 5 feet. 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 San Fernando Fault, located 6 mi northwest of Burbank's downtown, caused the 6.6 magnitude 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 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. During the Northridge earthquake in January 1994, more than 50 people were killed and the quake caused damage worth $35 billion. The 1971 San Fernando Earthquake. Mandatory Credit: Al Markado/ The Los Angeles Times/ ME.Quake71.2.1Ð22Ðm2.7.$. More than once have dams failed or were overtopped due to the shaking of large earthquakes - with devastating consequences for the people living downstream. 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. 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. The dam, which crumbled during the earthquake and during the following aftershocks, held approximately 3.6 billion gallons of water. Such faults, which are unknown but can produce devastating quakes, are called blind thrust faults. The earthquake caused over $500 million in damages, around 64 deaths, and critical destruction to the infrastructure of the region. 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