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. A magnitude-6.6 earthquake was shaking his home nestled at the bottom of the dam. After checking on his wife and child, he drove to the top of the dam to examine the damage. “It was hard to believe what I saw,” he said.
The Lower Van Norman Dam, which sat above the San Fernando Valley in Los Angeles County, had nearly collapsed in the wake of the quake. “As wind-whipped waves chewed at the damaged lip of the 1,100-foot Van Norman Dam, police spread through a nine-square-mile area between the reservoir and the Ventura Freeway, warning residents to evacuate,” The Los Angeles Times reported on February 10, 1971. Approximately 80,000 people did evacuate as officials lowered the water levels in the dam.
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. It led to 64 deaths and more than $500 million in damage. It prompted Governor Ronald Reagan to declare Los Angeles County a disaster area and President Richard Nixon to send Vice President Spiro Agnew to inspect the area.
After the San Fernando earthquake, the State of California enacted the Alquist Priolo Act to limit construction along faults that likely caused earthquakes able to rupture the ground surface in the last 11,000 years.
On the federal level, Congress renewed its interest in earthquake safety, held hearings and introduced new bills to establish a national earthquake research program. Congress eventually passed the Earthquake Hazards Reduction Act of 1977, which led to the National Earthquake Hazards Reduction Program, or NEHRP, and was pivotal in helping establish what is now the USGS Earthquake Hazards Program.
Over the years, NEHRP agencies, including the Federal Emergency Management Agency (FEMA), the National Institute of Standards and Technology, the National Science Foundation and the U.S. Geological Survey, made research and policy recommendations that in part contributed to the City of Los Angeles enacting an ordinance in 2015 to retrofit weaker first-story wood-frame buildings and non-ductile, or brittle, concrete buildings, which are both more vulnerable to collapse during strong shaking. In 2013, San Francisco enacted the Mandatory Soft Story Retrofit Program, which was based in part on work sponsored by NEHRP and on the aftermath of the 1989 Loma Prieta earthquake.
“NEHRP was founded on the belief that while earthquakes are inevitable, there is much that we can do as a nation to improve public safety, reduce losses and impacts and increase our resilience to earthquakes and related hazards,“ Gavin Hayes, the USGS senior science advisor for Earthquake and Geologic Hazards, said.
An unforgettable earthquake
An earthquake large enough to spur legislative action and help form new federal programs garnered much media attention.
“A Major Disaster,” the New York Times printed on Feb 10, 1971. “Quake Cost in Death, Damages Staggering,” the Valley News and Valley Green Sheet declared on Feb 11.
The latter newspaper printed an article that captured the quake’s desolation in a paragraph. “The cities of San Fernando and Sylmar were left in shambles. Some destruction was reported throughout the Newhall and Saugus areas, 10 miles west of the quake’s epicenter. And the destruction spread, almost like the ring on a pond after the rock’s initial splash.”
North-Trending fracture pattern near the Sylmar Converter Station above the upon Van Norman Dam. The fracture was due to a landslide and the dam’s setting in extensive fill material. Photo taken from a view looking northeast on Feb 10, 1971.
(Credit: USGS. Public domain.)
The earthquake was the first disaster in the United States to happen after the Disaster Relief Act of 1970, which directed federal agencies to provide assistance to state and local governments. At the time of the earthquake, FEMA did not exist.
The epicenter of the quake was about 8.7 miles (14 km) north of San Fernando in a sparsely populated area of the San Gabriel Mountains. It was 5.6 miles (9 km) deep and generally felt over approximately 80,000 square miles (208,000 square km) of California, Nevada and Arizona.
More than 200 aftershocks with a magnitude of 3 or more occurred over the next month. The upper San Fernando Valley, including the northern section of the City of Los Angeles, sustained the most severe damage to buildings and utilities.
There were 64 causalities directly related to the earthquake, with 49 people killed at the San Fernando Veterans Administration Hospital. Two of its buildings were completely destroyed by the quake. Others died at Olive View Hospital, under collapsed freeway overpasses and at other locations. At Olive View, four 5-story wings pulled away from the main building and three of them toppled.
Two fallen structurally separated stair towers and the collapsed basement at Olive View Hospital after the San Fernando earthquake in February 1971. View is north.
(Credit: USGS. Public domain.)
Photo of San Fernando Veterans Administration Hospital in Sylmar from the publication, “Engineering Aspects of the 1971 San Fernando Earthquake,” published by the U.S. Department of Commerce’s National Bureau of Standards in December 1971. The hospital’s roof collapsed and the shaking caused damage to the vertical pillars at the corners of the building.
In front of the San Fernando Valley Juvenile Hall facilities, railroad tracks were twisted, broken and displaced as much as 4 feet (1.2 m) from the intense shaking.
Photo showing railroad track damage following the San Fernando Earthquake on February 9, 1971.
(Credit: USGS. Public domain.)
Major freeways and traffic arteries in the northern San Fernando Valley were closed following the earthquake because of pavement fissures and collapsed bridges blocking lanes.
The California Department of Transportation adopted seismic design practices using lessons learned from the San Fernando earthquake. The agency created a Post-Earthquake Investigation Team that examines damage to bridges after all earthquakes and makes recommendations. CalTrans creates and implements seismic design criteria for infrastructure across the state.
Oblique aerial view of collapsed highway overpasses and bridges at the interchange of the Foothill and Golden State Freeways after the San Fernando earthquake in February 1971. The principal highway link between northern and southern California was temporarily cut and traffic had to be re-routed for several months.
(Credit: R. E. Wallace, USGS. Public domain.)
“I remember biking on the [not yet open] 210 freeway and seeing damaged bridges including near Foothill Boulevard, which had mushroomed columns,” Glenn Biasi, a scientist at the USGS, said.
Biasi’s home in Sunland, about 11 miles (18 km) from the epicenter, was damaged in the earthquake. He also recalled seeing people during the recovery phase salvaging used lumber from destroyed homes in San Fernando.
Margaret Vinci, manager of the Office of Earthquake Programs at the California Institute of Technology, was living in Arcadia, about 30 miles (48 km) from Sylmar, at the time of the earthquake and although her home had no damage, her relatives in the San Fernando Valley really struggled with repairs. “It took them months to recover,” Vinci said. She recalled her aunt’s home in Reseda was so damaged that her aunt had to live with Vinci immediately after the quake. “Her front yard was a plot of mud for weeks because of broken pipes,” Vinci said.
It was the cacophony of toppling and shaking appliances, dressers and other household items that Doug Given, a geophysicist with the USGS, remembers from the earthquake. Given, still in bed at home when the quake struck Glendale, pulled the covers over his head to drown out the noise. After the 12-second temblor, Given biked to downtown Glendale and recalled seeing broken glass and tumbled bricks.
Eyewitnesses are valuable during an earthquake and can help scientists understand the intensity of the shaking for areas near and far from the quake’s epicenter. Although people nowadays can easily submit “felt reports” to USGS through the Did You Feel It portal, which launched in 1999, in 1971, people would have sent in postcard surveys like the one below detailing their experience.
Survey sent in as part of postcard to report feeling the Northridge earthquake of 1994. These types of surveys predate the now online Did You Feel It portal.
Even though the San Fernando quake was 50 years ago, 28 years before the invention of the Did You Feel it portal, more than 1,000 people have submitted retroactive electronic reports so far.
These felt reports help support critical USGS products like ShakeMap, which provides near-real-time maps of ground motion and shaking intensity following significant earthquakes, and the Prompt Assessment of Global Earthquakes for Response (PAGER) system, which provides fatality and economic loss impact estimates for significant earthquakes worldwide.
Measuring the quake
In addition to eyewitness accounts, scientists look to seismographs to determine the size, or magnitude, of an earthquake and the subsequent intensity of ground shaking. The instruments measure the shaking’s amplitude, frequency and duration at various locations and distances from the earthquake, which gives scientists and decision makers an idea of ground and building motions, as well as potential damage, across an affected region.
There were more than 250 strong-motion seismographs around Southern California at the time of the San Fernando earthquake. Most of them were privately owned but maintained by the then-Seismological Field Survey unit of the National Oceanic and Atmospheric Administration’s National Ocean Survey as part of a cooperative network.
These seismographs provided a wealth of data to better characterize the ground motion and help scientists understand how structures responded to the ground motion. The data points helped answer fundamental questions in earthquake engineering, such as how does local geology affect ground motion? What ground motion characteristics are most damaging to buildings, bridges, dams and other engineered structures?
The San Fernando earthquake was the first to record more than 1-g of acceleration in a horizontal direction, which happened on a seismograph at the abutment of Pacoima Dam. Before that point, the maximum thought reasonable was much lower. Since then, many higher recordings have been made, but in the history of strong motion seismology, San Fernando was a turning point.
Southern California has a tumultuous tectonic past dating back tens of millions of years. Its crustal movements are an ongoing part of a pattern of deformation ultimately responsible for the San Fernando earthquake as well as California’s reputation as a shaky state.
Although most people think of the San Andreas Fault system when they think of a California quake, the San Fernando earthquake actually occurred on a less well-known fault system called the Sierra Madre Fault Zone, which runs along the base of the San Gabriel Mountains. The 1971 earthquake ruptured a subsection named the San Fernando Fault Zone, which extends from the western San Fernando Valley to Big Tujunga Wash, about 12 and a half miles (20 km) across.
The San Fernando Fault is a thrust fault, which means a section of land above the fault moved up and over a region below it. The earthquake was a single episode of ongoing crustal deformation, which, in a local sense, has pushed the San Gabriel Mountains up and south towards the broader Los Angeles Basin. In a broader sense, this motion is consistent with the plate boundary along the San Andreas Fault, where the plate to the west is moving northward relative to the plate on the eastern side at two inches (52 mm) per year.
During the quake, the mountains lurched as much as 5 feet to the south in a matter of seconds, damaging roadways, pipelines and other structures embedded in the ground, and leaving a discontinuous tear where the fault ruptured the ground surface across the mountain front.
Severe ground fractures and land sliding caused extensive damage in areas away from the fault itself, which is a common phenomenon for earthquakes of this magnitude. Landslides on very gentle slopes, known as lateral spreads and related to a process called liquefaction, happened in swaths of the northwestern San Fernando Valley. Though less visually dramatic, these caused significant damage to pipes and other infrastructure.
In steeper terrain, more than 1,000 landslides and rockfalls were identified and mapped from aerial images. They were concentrated in the foothills and mountainous areas of the San Gabriel Mountains. One of largest slides occurred on the east side of Schwartz Canyon and was approximately 600 feet (180 m) wide.
A path to earthquake legislation
Seven years before Southern California was rocked by the San Fernando earthquake, the most powerful recorded earthquake in U.S. history hit the state of Alaska. The magnitude-9.2 quake hit Prince William Sound on March 27, 1964, at 5:36 p.m. local time and ruptured for about 4.5 minutes. The quake triggered a major tsunami that caused death and destruction from the Kodiak Islands to northern California.
Although the mighty Alaska quake took place in a sparsely populated area, it demonstrated the potential for devastation in other parts of the country and started the conversation toward a coordinated federal program focused on earthquake risk mitigation and response.
The San Fernando earthquake revitalized those talks and helped push forward what eventually became NEHRP in 1977. The bill created an Office of Earthquake Hazard Reduction that eventually became the USGS Earthquake Hazards Program. The program works with partners to monitor and report earthquakes, assess earthquake impacts and hazards and perform research into the causes and effects of earthquakes.
Since NEHRP’s inception in 1977, it has been reviewed and reauthorized by Congress many times. The four agencies that currently lead the effort, including FEMA , the National Institute of Standards and Technology, the National Science Foundation and the USGS, are each tasked with specific roles.
Most recently, NEHRP was reauthorized and signed into law in December 2018. This most recent bill expands its purview to bolster communities’ ability to prepare for, recover from and adapt to earthquakes and publish maps of active faults and other seismically induced hazards. It also continues to support and develop the Advanced National Seismic System, including the ShakeAlert earthquake early earning system, which is now operational throughout California, Oregon and Washington.