The overall fault displacement was summarized by geologist Barclay Kamb and others as "nearly equal amounts of north–south compression, vertical uplift (north side up), and left lateral slip and hence may be described as a thrusting of a northern block to the southwest over a southern block, along a fault surface dipping about 45° north. And it was a reinforced concrete building with kind of an open first story. The Antelope Valley Freeway had damage from Newhall Pass to the northeast, primarily from settling and alignment issues, as well as splintering and cracking at the Santa Clara River and Solemint bridges. We sat down with the Director of Caltech’s Earthquake Engineering Research Laboratory and Professor Emeritus of Engineering Seismology, Dr. Thomas Heaton, to better understand what happened 50 years ago, what we learned from it, and how we can better alert the public. [30], California Strong Motion Instrumentation Program, Prior to the San Fernando earthquake, some structural engineers had already believed that the existing groundwork for seismic design required enhancement. So, for instance, if you have got a column and you’ve got a beam, and you've got steel running along those things to keep it from falling apart, if the steel just pulls out at the end of the beam, out from the column, you're going to lose the connection, you'll lose the building. [23], Both the Upper and Lower Van Norman dams were severely damaged as a result of the earthquake. Figure 2: Earthquakes on two blind thrust faults caused severe damage in the San Fernando Valley. The success in this area spurred the initiation of California's Strong Motion Instrumentation Program. Soil liquefaction played a role within confined areas of the slide, but it was not responsible for all the motion at the site, and tectonic slip of faults in the area was also excluded as a cause. Afterwards, they told people you have to put a hook in the rebar so that you positively connect the rebar from the column to the rebar from the beam. Along the hill fronts of the Tujunga segment some ambiguous formations were present because some scarps may have had influence from downhill motion, but for the most part they were tectonic in nature. It led to 64 deaths and more than $500 million in damage. They’re one story tall, no windows, just solid concrete walls. Schools were affected, as they had been during the 1933 Long Beach earthquake, but this time amended construction styles improved the outcome for the thousands of school buildings in the Los Angeles area. The fix had to do not so much with changing the concrete or the steel, but the way they connect all the steel together inside the concrete. Ground displacement damaged sidewalks and roads, with cracks in the more rigid asphalt and concrete often exceeding the width of the shift in the underlying soil. The San Fernando earthquake — like virtually all earthquakes — was caused by sudden displacement of rock masses along a fault. 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. If that fault ever duplicates its great 1811 quake (which caused the great river to flow backwards), look for the possible deaths of millions. Shaking from the M6.5 quake caused a hospital to collapse, killing dozens of people. The 6.6 magnitude earthquake killed more than 60 people on February 9, 1971. 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. 2). The duration of strong ground motion at that location was probably similar to the 12 seconds observed at the Pacoima Dam, and it is thought that another few seconds' shaking might have been enough to bring the building to collapse. Although the complete Sierra Madre Fault Zone had previously been mapped and classified by name into its constituent faults, the clusters of fault breaks provided a natural way to identify and refer to each section. Fifty years ago — Feb. 9, 1971 — several of the hospital’s many buildings there, along with other structures throughout the San Fernando Valley and other parts of Los Angeles county, collapsed or were severely damaged by a 6.6 magnitude earthquake. All they knew was that communications were out with that part of the world and it was a big problem for Los Angeles to respond to that. The group of one-story structures 300 feet west of the new facility, and some other buildings, were not damaged. In the vicinity of the Sylmar Fault segment, there was a low possibility of landslides due to a lack of elevation change, but in the foothills and mountainous area a large amount of landsliding occurred and more work was necessary to eliminate the possibility of misidentifying a feature. And by the time of the Northridge earthquake, we had made quite a bit of progress, but our budgets were pretty limited still and we weren't doing what we call real early warning... After the Northridge Earthquake, we got some important grants through FEMA and we were able to really beef up the seismic system, and when we beefed it up, we specifically planned that the hardware would be able to do what we call early warning, send the strong shaking in real time, and collect it so we could analyze it... Now we're at a point where we can tell you the shakiness is happening in California, and we can tell you the shaking is on its way, and that's the ShakeAlert project. Some canals in the area of the dams were damaged and not usable, and dikes experienced slumping but these did not present a hazard. Cracks formed in the rocks and a rock slide came within 15 feet (4.6 m) of the apparatus, and the foundation remained undamaged, but a small (half-degree) tilt of the unit was discovered that was apparently responsible for closing the horizontal pendulum contacts. They just take a fire hose on a Hillside and slurry the mud into someplace and let it settle, but it doesn't make a very stable slope. Two were due to power failure of life-support systems and one, that of an employee who was struck by part of the collapsing building as he or she tried to exit the building, was a direct result of the destruction. The area where the heaviest effects were present was limited by geographical features on the three remaining margins, with the Santa Susana Mountains on the west, the Santa Monica Mountains and the Los Angeles River to the south, and along the Verdugo Mountains to the east. [15], In repeated measurements of the different fault breaks, the results remained consistent, leading to the belief that most of the slip had occurred during the mainshock. The area where the heaviest effects were present was limited by geographical features on the three remaining margins, with the Santa Susana Mountains on the west, the Also often known as the San Fernando earthquake, the Feb. 8, 1971, magnitude-6.5 quake occurred on a Tuesday at about 6:01 a.m. Its origin was in the … Since both occurred in urban and industrial areas and resulted in significant economic impairment, each event drew critical observation from planning authorities, and has been thoroughly studied in the scientific communities. The event was one in a series that affected Los Angeles county in the late 20th century. Transportation around the Los Angeles area was severely afflicted with roadway failures and the partial collapse of several major freeway interchanges. [19], The instrument that was installed at the Pacoima Dam recorded a peak horizontal acceleration of 1.25 g, a value that was twice as large as anything ever seen from an earthquake. The frontal fault system at the base of the San Gabriel Mountains extends from the San Jacinto Fault Zone in the east to offshore Malibu in the west, and is defined primarily by moderate to shallow north-dipping faults, with a conservative vertical displacement estimated at 4,000–5,000 feet (1,200–1,500 m). The magnitude 6.6 earthquake left 65 dead; injured another 2,000 people and caused half a billion dollars in damage (about $3.2 billion today). Download it here. From left: Duane L. Georgeson, Jules Bergman examine damage in the aftermath of the Sylmar Earthquake / 1971 San Fernando earthquake, in the Walt Disney Television via Getty Images / … More than 400 portable classrooms and 53 wood frame pre-Field Act buildings were also in use. Workers clear debris and rubble from collapsed buildings at the Veteran's Hospital in the Los Angeles neighborhood of Sylmar, Calif., after a massive earthquake hit the area on Feb. 9, 1971. The domain of the ranges stretches from the Channel Islands offshore, to the Little San Bernardino Mountains, 300 miles (480 km) to the east. [8][9] The unanticipated thrust earthquake had a magnitude of 6.5 on the Ms scale and 6.6 on the Mw scale, and a maximum Mercalli intensity of XI (Extreme). The one-story Foothill Nursing Home sat very close to a section of the fault that broke the surface and was raised up three feet higher than the street. The complete structure, including the four external staircases, could be considered five separate buildings, because the stair towers were detached from the main building by about four inches. Considerable damage was seen in localized portions of the valley and also in the foothills of the San Gabriel Mountains above the fault block. The initial surveyors of the extensive faulting in the valley, foothills, and mountains reported only tectonic faulting, while excluding fissures and other features that arose from the effects of compaction and landsliding. [6] The origin of faulting was located five miles north of the San Fernando Valley. To learn more about protecting your house, go to StrengthenMyHouse.com. Electrical power and communications failed at the hospital at the time of the earthquake, but very few people occupied the lower floors and the stairways at the early hour. Highly shattered rock was also documented along the ridge tops, and rockfalls (which continued for several days) were the result of both the initial shock and the aftershocks. It's called hydraulic fill, a kind of mining they used to do. And people were kind of surprised to see how it collapsed. So in the '80s, I was with the U.S. Geological Survey, and I was trying to push our office in Caltech towards having better systems to react during the earthquake itself. The Field Act was put into effect just one month following the destructive March 1933 Long Beach earthquake that damaged many public school buildings in Long Beach, Compton, and Whittier. The most frequently-encountered type of slide was the surficial (less than 3 feet (0.91 m) thick) debris slides and were most often encountered on terrain consisting of sedimentary rock. The accelerometer was mounted on a concrete platform on a granite ridge just above one of the arch dam's abutments. The fault that was responsible for the movement was not one that had been considered a threat, and this highlighted the urgency to identify other similar faults in the Los Angeles metropolitan area. The movement contributed to heavy damage at the Sylmar Juvenile Hall facility, Sylmar Converter Station, and the Metropolitan Water District Treatment Plant, but its effects on the interchange was not completely understood as of a 1971 report from the California Institute of Technology. Estimates are that 10,000 people would have perished in that disaster ... And rather fortuitously, the Department of Water and Power, which owned that reservoir, had decided months earlier to decrease the capacity of the dam by 40 feet. They tried maybe half a dozen times until finally Eric Garcetti and Lucy Jones kind of put together the politics to actually get through a retrofit for these brittle concrete buildings. Today, some older buildings and homes still are not strong enough to withstand earthquake damage. The hospital was staffed by 98 employees and had 606 patients at the time of the earthquake; all three deaths that occurred at the Olive View complex were in this building. But I think it's got another couple of decades before the owners have to actually retrofit these things. The area of surface breaks on the ground at the site was 900 ft (270 m) (at its widest) and stretched 4,000 ft (1,200 m) down a 1% grade slope towards the southwest. But the lessons learned from the great 1971 San Fernando earthquake remained strictly a local education. They're short. The culprit in this case was a zone of fractures that has become known as the San Fernando fault, which likes along the northern boundary of the San Fernando Valley (Fig. Get the best experience and stay connected to your community with our Spectrum News app. 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. He couldn’t. [15][16], All segments shared the common elements of thrust faulting with a component of left-lateral slip, a general east–west strike and a northward dip, but they were not unified with regard to their connection to the associated underlying bedrock. As categorized during the intensive studies immediately following the earthquake, they were labeled the Mission Wells segment, Sylmar segment, Tujunga segment, Foothills area, and the Veterans fault. The total surface rupture was roughly 19 km (12 miles) long. You just know they’ll happen. The Olive View Medical Center and Veterans Hospital both experienced very heavy damage, and buildings collapsed at both sites, causing the majority of deaths that occurred. This stipulation ultimately found its way into the Uniform Building Code as an appendix several years later. Our new Spectrum News app is the most convenient way to get the stories that matter to you. Another result of the event involved the hundreds of various types of landslides that were documented in the San Gabriel Mountains. Fortunately, there was six feet. FAULT INVOLVED: San Fernando fault zone; minor offset reported on the eastern Santa Susana fault zone Also known as the Sylmar Earthquake, this earthquake occurred on the San Fernando fault zone, a zone of thrust faulting which broke the surface in the Sylmar-San Fernando Area. By the late 1980s, the program had instrumented more than 450 structures, bridges, dams, and power plants. 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. The extraordinarily high acceleration was just one part of the picture, considering that duration and frequency of shaking also play a role in how much damage can occur. Casualties in these highly affected areas might have increased had the shock occurred later in the day. Few of the slides that were logged from the air were also observed from the ground. [22], The Veterans Administration Hospital entered into service as a tuberculosis hospital in 1926 and became a general hospital in the 1960s. One of the hardest-hit buildings was the just-completed San Fernando Veterans Administration Hospital, whose unreinforced concrete wings collapsed, killing at … Part of the reason there were so many stations to capture the event was a 1965 ordinance that required newly constructed buildings in Beverly Hills and Los Angeles over six stories in height to be outfitted with three of the instruments. The building was not in use and remained standing. The statistics of earthquakes are very much like, believe it or not, epidemics and pandemics. As much as 5 ft (1.5 m) of lateral motion was observed on either end of the slide, and trenches that were excavated during the examination at the site revealed that some of the cracks were up to 15 ft (4.6 m) deep. “The San Fernando earthquake led to more policy changes than probably any other earthquake that we’ve had,” says Dr. Lucy Jones, a Southern California-based seismologist and author . The two facilities, located near Grapevine and Weldon canyons that channel water and debris off the Sierra Madre Mountains, are lined by steep ridges and have formed alluvial fans at their mouths. The five-story, reinforced-concrete Medical Treatment and Care Building was one of three new additions to the complex (all three of which sustained damage), was assembled with earthquake-resistant construction techniques, and was completed in December 1970. Vibration caused two of the bridge's 191-foot sections to fall from a maximum height of 140 ft (43 m), along with one of the supporting pillars. Several instances of failure or collapse at the site took place and two men were killed while driving in a pickup truck as a result. You can look at some statistics, and the statistics are something we call a Pareto distribution, which means that the biggest events, biggest earthquakes, biggest pandemics are the ones that really matter, and they don't happen very often. The Transverse Ranges form the perimeter of a series of basins that begins with the Santa Barbara Channel on the west end. Fifty years in the past this week, the lethal Sylmar earthquake rattled Southern California, leaving dozens of individuals lifeless and inflicting greater than $500 million in property harm. Next week marks 50 years since the 1971 San Fernando earthquake. At 2 mi (3.2 km), Hubbard Street Elementary School was the closest school to Pacoima dam, and was also less than a mile from the Veterans Hospital complex. Ground displacement at the site was ruled out as a major cause of the failure, and in addition to the fallen sections and a crane that was struck during the collapse, other portions of the overpass were also damaged. Additional breaks occurred farther to the east that were in a more scattered fashion, while the western portion of the most affected area had less pronounced scarps, especially the detached Mission Wells segment. The Van Norman Reservoir is up in the northern part of the San Fernando Valley, and it's where the Los Angeles Aqueduct comes in, and it was designed to be storage of water in case the aqueduct was broken by the San Andreas fault, believe it or not. “It was hard to believe what I saw,” he The 1979 Imperial Valley and 1987 Whittier Narrows earthquakes were presented as gainful events that were recorded during that period, because both produced valuable data that increased knowledge of how moderate events affect buildings. The damage at the lower dam consisted of a landslide that dislocated a section of the embankment. Fifty years ago this week, the deadly Sylmar earthquake rattled Southern California, leaving dozens of people dead and causing more than $500 million in property damage. Shear cracking occurred at the column closest to the western abutment, and the ground at the same column's base exhibited evidence of rotation. So they made the dam that way and in the ‘71 earthquake when it shook hard the mud like material re-liquefied and then the front of the dam just kind of slumped into the reservoir. Fifty years ago today, February 9, 1971, occurred the deadly and devastating San Fernando Earthquake, aka the Sylmar Quake. A magnitude-6.6 earthquake was shaking his home nestled at the bottom of the dam. (AP Photo). The earthen lip of the dam fell into the reservoir and brought with it the concrete lining, while what remained of the dam was just 5 feet (1.5 m) above the water level. Known as the San Fernando earthquake or the Sylmar earthquake, it caused 58 deaths and more than $500 million in damage. 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. [10], Paleomagnetic evidence has shown that the western Transverse Ranges were formed as the Pacific Plate moved northward relative to the North American Plate. An inspection of the lower dam in 1964 paved the way towards an arrangement between the State of California and the Los Angeles Department of Water and Power that would maintain the reservoir's water level that was reduced 10 feet lower than was typical. Since it is presumed that surface rupture will likely take place where past surface displacement has occurred, the state geologist was given the responsibility for evaluating and mapping faults that had evidence of Holocene rupture, and creating regulatory zones around them called Earthquake Fault Zones. Unlike the situation at the Antelope Valley Interchange, permanent ground movement (defined as several inches of left-lateral displacement with possibly an element of thrusting) was observed in the area. The buildings at both facilities were constructed with mixed styles, but engineers were unable to thoroughly study the buildings' responses because they were not outfitted with instruments for recording strong ground motion, and this prompted the Veterans Administration to later install seismometers at its high-risk sites. But fixing your walls is nothing compared to losing the house. All the walls are tied together with steel, and then you tie it all together on the roof. Although instruments had recorded a force of .33g during the 1940 El Centro earthquake, building codes only required structures to withstand a lateral force of .1g as late as the 1960s. As a result of what was considered a fortunate accident, the machine kept recording for six minutes (until it ran out of paper) and provided scientists with additional data on 30 of the initial aftershocks. Earthquake bracing used in the building's second through fifth floors consisted of shear walls, but a rarely used slip joint technique used with the concrete walls at the first floor kept them from being part of that system. [25], Substantial disruption to about 10 miles of freeways in the northern San Fernando Valley took place, with most of the damage occurring at the Foothill Freeway / Golden State Freeway interchange, and along a five-mile stretch of Interstate 210. In addition to the collapse of the stairways, the elevators were out of commission. The act restricts construction of buildings designed for human occupancy across potentially active faults. The two blue lines mark the faults which ruptured in the San Fernando earthquake 46 years ago today. The damaged buildings variously were wood-frame and masonry structures. As of 1973, a few of the highest risk (26 were completed in zone 3 alone) sites that had been completed were in Seattle, Memphis, Charleston, and Boston. [28], At Los Angeles High School (20 mi (32 km) from Pacoima Dam) where the exterior walls of the main pre-Field Act building (constructed 1917) were unreinforced brick masonry, long portions of the parapet and the associated brick veneer broke off and some fragments fell through the roof to a lower floor, while other material landed on an exit stairway and into a courtyard area. Even if you recorded them, you couldn’t read them. But the Sylmar quake steered the Southern California region into implementing new and safer building codes to enhance public safety, advanced earthquake technology, and, according to Caltech, led to a coalition of the United States Geological Survey (USGS) and the university in expanding seismic monitoring through the region. So they lowered the water level 40 feet because they were thinking perhaps it was not very good in an earthquake, and if that decision hadn’t been made, it would have been a completely different event. [24], Differential ground motion and strong shaking (MMI VIII (Severe)) were responsible for serious damage to the Sylmar Juvenile Hall facility and the Sylmar Converter Station (both located close to the Upper Van Norman lake). Other sites throughout the Los Angeles area had been instrumented as a result of local ordinances, and an extraordinary amount of strong motion data was recorded, more so than any other event up until that time. [14], Prominent surface faulting trending N72°W was observed along the San Fernando Fault Zone from a point south of Sylmar, stretching nearly continuously for 6 miles (9.7 km) east to the Little Tujunga Canyon. [11], The San Fernando earthquake occurred on February 9, 1971, at 6:00:41 am Pacific Standard Time (14:00:41 UTC) with a strong ground motion duration of about 12 seconds as recorded by seismometers,[12] although the whole event was reported to have lasted about 60 seconds. The California Strong Motion Instrumentation Program was initiated in 1971 with the goal of maximizing the volume of data by furnishing and maintaining instruments at selected lifeline structures, buildings, and ground response stations. [24], The upper dam was constructed in 1921 with the hydraulic fill process, three years after the larger lower dam, which was fabricated using the same style. The success of the Imperial Valley event was especially pronounced because of a recently constructed and fully instrumented government building that was shaken to the point of failure. [22], The Medical Treatment and Care Building included a basement that was exposed (above grade) on the east and south sides, mixed (above and below grade) on the west side, and below grade on the north side of the building, the variation being due to the shallow slope at the site. So the things that matter the most are very rare, and you have no idea when the next one's going to be. The wood frame buildings (classrooms, a multipurpose building, and some bungalows) were built after the Field Act, and damage and cleanup costs there totaled $42,000. As had happened following other earthquakes in California, legislation related to building codes was once again revised, with laws that specifically addressed the construction of homes or businesses near known active fault zones. You never know when the next one's going to come in. The event affected a number of health-care facilities in Sylmar, San Fernando, and other densely populated areas north of central Los Angeles. Moving eastward, there is the Ventura Basin, the San Fernando Valley, and the San Gabriel Basin, with active reverse faults (San Cayetano, Red Mountain, Santa Susana, and Sierra Madre) all lining the north boundary.
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