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what caused the 1971 san fernando earthquake
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. The main building was demolished at a cost of $127,000, and none of the various post-Field Act buildings were damaged at the site. The act restricts construction of buildings designed for human occupancy across potentially active faults. Gas lines were broken and separation of the buildings' porches was due to lateral displacement of up to six inches. The statistics of earthquakes are very much like, believe it or not, epidemics and pandemics. It had been established that these zones had a higher likelihood of experiencing strong ground acceleration, and the plan was made to furnish the selected VA hospitals with two instruments. [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 domain of the ranges stretches from the Channel Islands offshore, to the Little San Bernardino Mountains, 300 miles (480 km) to the east. Tuesday marks 50 years since the 1971 Sylmar-San Fernando earthquake unleashed its fury on Los Angeles just after 6 a.m. 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 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. 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. ... where it caused huge damage to the old Olive View Hospital. 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. When builders build houses, they put in all this additional bracing [in the floors] so that it's stiff enough that it doesn't flex much when you put a load in it. Even at that time, engineers were against the idea of constructing buildings to resist the high forces that were seen in the El Centro shock, but after a 1966 earthquake peaked at .5g, and a maximum of 1.25g was observed at the Pacoima Dam during the San Fernando event, debate began as to whether that low requirement was sufficient. 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 red line is the fault on which the Northridge quake occurred in 1994. The upper lake subsided 3 feet (0.91 m) and was displaced about 5 feet (1.5 m) as a result of the ground movement, and the dam's concrete lining cracked and slumped. 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. Uplift and other effects affected private homes and businesses. Analysis revealed that the earthquake triggered over 1,000 landslides. “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 building was not in use and remained standing. ... known as the San Fernando or Sylmar Earthquake. 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. This made the earthquake the most documented event, at the time, in terms of strong-motion seismology; by comparison, the 1964 Alaska earthquake did not provide any strong motion records. The San Gabriel Mountains are a 37.3 mi (60.0 km) long portion of the Transverse Ranges and are bordered on the north by the San Andreas Fault, on the south by the Cucamonga Fault, and on the southwest side by the Sierra Madre Fault. By the late 1980s, the program had instrumented more than 450 structures, bridges, dams, and power plants. The hospital buildings, the freeway overpasses, and the Sylmar Juvenile Hall were on coarse alluvium that overlay thousands of feet of loosely consolidated sedimentary material. 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. 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. [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. All these buildings had been previously inspected with regard to the requirements of the Act, and many were reinforced or rebuilt at that time, but earthquake engineering experts recommended further immediate refurbishment or demolition after a separate evaluation was done after the February 1971 earthquake, and within a year and a half the district followed through with the direction with regard to about 100 structures. The difference in rigidity at the second floor was proposed as a cause of the considerable damage to the lower levels. But I think it's got another couple of decades before the owners have to actually retrofit these things. [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. Fifty years ago today, February 9, 1971, occurred the deadly and devastating San Fernando Earthquake, aka the Sylmar Quake. 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. 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. 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 slides ranged from 49–984 feet (15–300 m) in length, and could be further categorized as rock falls, soil falls, debris slides, avalanches, and slumps. 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. Since the collapse of the dam lowered its overall height, the decision to reduce its capacity proved to be a valuable bit of insurance. He couldn’t. Even if you recorded them, you couldnât read them. The February 9, 1971 San Fernando earthquake was the first to cause significant damage within the LA region since the rapid growth of the 1940’s-60’s. 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. 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. 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. 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. 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. Old footage of some of the destruction resulting from the 1971 San Fernando earthquake. The concreteâs made out of concrete block, and then you put rebar down the center cells, and then they pour concrete to turn it into a solid concrete wall. Today, some older buildings and homes still are not strong enough to withstand earthquake damage. Learn More. 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 event was one in a series that affected Los Angeles county in the late 20th century. 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. [26], While the Newhall Pass interchange was still under construction at the time of the earthquake, the requisite components of the overpass were complete. [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. [18], In early 1971, the San Fernando Valley was the scene of a dense network of strong-motion seismometers, which provided a total of 241 seismograms. 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 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. Accentuated damage near alluvium had been documented during the investigation of the effects of the 1969 Santa Rosa earthquakes. [21], Federal, county, and private hospitals suffered varying degrees of damage, with four major facilities in the San Fernando Valley suffering structural damage, and two of those collapsing. The areas that were affected by the strongest shaking were the outlying communities north of Los Angeles that are bounded by the northern edge of the San Fernando Valley at the base of the San Gabriel Mountains. Fred Iversen holds a historic clock recovered from a hospital that collapsed during the 1971 Sylmar earthquake. So when the earthquake happened, the Caltech seismological laboratory was basically blind... People didn't realize that those hospitals had fallen down or what was going on with the reservoir. 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. 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 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. [27], The large number of public school buildings in the Los Angeles area displayed mixed responses to the shaking, and those that were built after the enforcement of the Field Act clearly showed the results of the reformed construction styles. A magnitude-6.6 earthquake was shaking his home nestled at the bottom of the dam. 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. 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. And people were kind of surprised to see how it collapsed. 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. With a moment magnitude of 6.7, the Northridge earthquake was the strongest earthquake to strike the Los Angeles area since the 1971 San Fernando earthquake, which also had a magnitude of 6.7. The Los Angeles Department of Water and Power, as well as the County of Los Angeles, investigated and verified that local soil conditions contributed to the ground displacement and resulting destruction. Bryant, his 13-year-old daughter, Gianna, and six other passengers were flying from Orange County to a youth basketball tournament at his Mamba Sports Academy in Ventura County on Jan. 26, 2020, when the helicopter encountered thick fog in the San Fernando Valley north of Los Angeles. 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. [10], Paleomagnetic evidence has shown that the western Transverse Ranges were formed as the Pacific Plate moved northward relative to the North American Plate. [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). But fixing your walls is nothing compared to losing the house. Author irememberjfk_l6fq3c Posted on July 10, 2019 Categories The News. So, for instance, if you have got a column and youâve 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. But the lessons learned from the great 1971 San Fernando earthquake remained strictly a local education. 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. 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. 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. The greatest number of slides were centered to the southwest of the mainshock epicenter and close to the areas where surface faulting took place. The San Fernando earthquake, or Sylmar quake as it’s also called, killed 64 people, injured thousands more, and caused more than $500 million worth of damage. Damage to the building, including ceiling tiles, telephone equipment, and elevator doors, was excessive at the basement and the first floor, with little damage further up. 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 list of items needing improvements included building codes, dams and bridges being made more earthquake resistant, hospitals that are designed to remain operational, and the restriction of development near known fault zones. Loss of life that was directly attributable to the earthquake amounted to 58 (a number of heart attack and other health-related deaths were not included in this figure). 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. Few of the slides that were logged from the air were also observed from the ground. Shaking from the M6.5 quake caused a hospital to collapse, killing dozens of people. ShakeAlertLA to Be Replaced by Statewide Earthquake Early-Warning App, Residents of the Coachella Valley React to Salton Sea Swarm of Earthquakes, California Consumer Do Not Sell My Personal Information, On February 9, 1971, a 6.6-magnitude earthquake struck the San Fernando Valley, The Sylmar quake, as it's known, is one of the strongest earthquakes ever recorded in SoCal history, The quake killed 65 people, injured 2,000 more, and caused north of $500 million in property damage. The unincorporated districts of Newhall, Saugus, and Solemint Junction had moderate damage, even to newer buildings. One of the hardest-hit buildings was the just-completed San Fernando Veterans Administration Hospital, whose unreinforced concrete wings collapsed, killing at … Considerable damage was seen in localized portions of the valley and also in the foothills of the San Gabriel Mountains above the fault block. And it turns out that about 40 feet of the top of the dam slid in, and there was a six-foot leeway left to hold back the water. One unit would be installed within the structure and the second would be set up as a free-field unit located a short distance away from the facility. [22], Most of the buildings at the Los Angeles County–owned, 880-bed hospital complex had been built before the adoption of new construction techniques that had been put in place after the 1933 Long Beach earthquake. 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. So when an earthquake comes along, it's going to give you a big enough load that you have to fix all your walls. Theyâre one story tall, no windows, just solid concrete walls. Some canals in the area of the dams were damaged and not usable, and dikes experienced slumping but these did not present a hazard. 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. Except for the concrete gymnasium, all of the buildings at Sylmar High School (3.75 mi (6.04 km) from Pacoima Dam) were post-Field Act, one-story, wood construction. And when they built that reservoir, they sluiced dirt into the end of the valley. The estimate for repairs at the site was $485,000. 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. And it was a reinforced concrete building with kind of an open first story. It led to 64 deaths and more than $500 million in damage. It led to 64 deaths and more than $500 million in damage. Because the first floor almost collapsed, the building was leaning to the north by almost two feet, and three of the four concrete stair towers fell away from the main building. Known as the San Fernando earthquake or the Sylmar earthquake, it caused 58 deaths and more than $500 million in damage. The total surface rupture was roughly 19 km (12 miles) long. Though the reinforced concrete block structure was afflicted by the shock and uplift, the relatively good performance was in stark contrast to that of the Olive View and Veterans Hospital complexes. 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 damage at the lower dam consisted of a landslide that dislocated a section of the embankment. State and local agencies (as well as the property owner) were then responsible for enforcing or complying with the building restrictions. [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. Get the best experience and stay connected to your community with our Spectrum News app. 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. 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. EL SEGUNDO, Calif. â At 6 a.m. on February 9, 1971, a 6.6-magnitude earthquake struck the San Fernando Valley. (AP Photo). [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. Fortunately, there was six feet. [13], Several key attributes of the event were shared with the 1994 Northridge earthquake, considering both were brought about by thrust faults in the mountains north of Los Angeles, and each resulting earthquake being similar in magnitude, though no surface rupture occurred in 1994. Several landslides occurred between Balboa Boulevard and California State Route 14, but the most significant damage occurred at the two major interchanges. 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 After checking on his wife and child, he drove to the top of the dam to examine the damage. While lateral, transverse, and vertical motions were all observed, the largest individual component of movement was 5 ft 3 in (1.60 m) of left lateral slip near the middle of the Sylmar segment. Casualties in these highly affected areas might have increased had the shock occurred later in the day. [28], Following many of California's major earthquakes, lawmakers have acted quickly to develop legislation related to seismic safety. [29][30], Introduced as Senate Bill 520 and signed into law in December 1972, this legislation was originally known as the Alquist-Priolo Geologic Hazard Zones Act, and had the goal of reducing damage and losses due to surface fault ruptures or fault creep. 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. [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. Shear cracking occurred at the column closest to the western abutment, and the ground at the same column's base exhibited evidence of rotation. 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. After the M6.4 1933 Long Beach earthquake the Field Act was passed the following month, and after the 1989 Loma Prieta earthquake, the Seismic Hazards Mapping Act and Senate Bill 1953 (hospital safety requirements) were established. Forty-nine of the 64 deaths came from the San Fernando Veterans Administration Hospital, according to … 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. [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. [31][32], The San Gabriel Mountains with the Veterans Hospital complex in center (above) and selected cities with reported felt intensity in the United States (below), Ground level and overhead view of the scarp at the Foothill Nursing Home, Los Angeles Department of Water and Power, List of Los Angeles Unified School District schools, "Preliminary strong-motion results from the San Fernando earthquake of February 9, 1971", "50 years ago, the Sylmar earthquake shook L.A., and nothing's been the same since", "Tectonic setting of the San Gabriel mountains", "Seismically triggered landslides in the area above the San Fernando Valley", "The study of earthquake questions related to Veterans Administration hospital facilities", "Damage to constructed works, associated with soil movements and foundation failures", "Ground displacement at San Fernando Valley Juvenile Hall and the Sylmar Converter Station", "Highway damage in the San Fernando earthquake", "Earthquake damage to freeway structures", "History of the Alquist-Priolo Earthquake Fault Zoning Act, California, USA", "San Fernando 1971: M 6.6 – 10km SSW of Agua Dulce, CA", "Seismological studies of the San Fernando earthquake and their tectonic implications", "Strong motion data from the San Fernando, California, earthquake of February 9, 1971", "Pattern of faulting and nature of fault movement in the San Fernando earthquake", "Building damage in the San Fernando Valley", Historic Earthquakes – San Fernando, California, California Geological Survey – About CSMIP, Veterans Memorial Community Regional Park, Los Angeles County Department of Parks and Recreation, https://en.wikipedia.org/w/index.php?title=1971_San_Fernando_earthquake&oldid=1006200696, February 1971 events in the United States, Geology of Los Angeles County, California, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License, This page was last edited on 11 February 2021, at 16:18. Transportation around the Los Angeles area was severely afflicted with roadway failures and the partial collapse of several major freeway interchanges. There was a brand new hospital, the Olive View Hospital, that had just been completed, and they were just staffing it up, and it collapsed in the earthquake. 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 hadnât been made, it would have been a completely different event. 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. On February 9, 1971, a magnitude 6.6 earthquake shook the San Fernando Valley -- the first in the L.A. area in nearly 38 years -- caused major damage in the community of Sylmar. 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. On Interstate 5, the most significant damage was between the Newhall Pass interchange on the north end and the I-5 / I-405 interchange in the south, where subsidence at the bridge approaches and cracking and buckling of the roadway made it unusable. 2). The Transverse Ranges form the perimeter of a series of basins that begins with the Santa Barbara Channel on the west end. 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. 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.
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