The quake might not have been the Big One, but it still managed to wake California up to a danger that was largely unrecognized. The modern era of earthquake awareness and preparedness is deeply rooted in Sylmar. Before then, earthquakes were either removed in time — in San Francisco, in Long Beach — or physically distant — in Anchorage. The 6. You have this modern glistening city and all of a sudden hospitals are being knocked down.
At the Veterans Administration Hospital in Sylmar, two buildings dating to the s collapsed and several others were severely damaged, causing 49 of the 64 deaths attributed to the disaster. Less costly in lives, yet more startling to engineers and scientists, was the partial collapse of the 4-month-old Olive View Medical Center. Elevator towers tumbled, and the second floor of the bed psychiatric unit collapsed onto the first.
Three died there. No less shocking was the collapse of the soaring, nearly completed overpass from the new Antelope Valley Freeway Highway 14 to the Golden State Freeway Interstate 5 in Newhall Pass and portions of the Foothill Freeway I interchange, where two men in a pickup were killed. Another revelation was the damage to single-family homes, at the time thought to be resilient enough to ride out moderate quakes.
They proved helpless when the fault rupture reached the surface, a phenomenon that had not previously occurred in an urban earthquake. Full Coverage: 50 years after the Sylmar earthquake. The Times recalls how the quake that rumbled through L. For the seismic community, the near debacle of the Lower Van Norman Dam, causing no loss of life but forcing the evacuation of 80, people, was the most frightening lesson.
Luck may have played a part. The water level had been lowered 10 feet in after an evaluation had raised doubt about its stability. It galvanized both the state and the federal government. The near catastrophe led the California Division of Safety of Dams , an agency created after the failure of the St. Francis Dam , to tighten its standards to include liquefaction, resulting in dams across the state being retrofitted.
Within two years, the California Legislature responded with laws championed by state Sen. Alfred E. Alquist that required earthquake zones to be mapped and set new design standards for hospitals. The mapping law was later enhanced to include landslide and liquefaction zones. Until then, despite pressure from the seismic community, the U. Geological Survey had no program focused on risk reduction, Hough said. Fifty years ago, a 6. Hundreds of new sensors have been added to advance seismic knowledge, inform building codes and help in emergency response.
There were more than 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. 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 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, 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 feet m wide.
Seven years before Southern California was rocked by the San Fernando earthquake, the most powerful recorded earthquake in U. The magnitude 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 program works with partners to monitor and report earthquakes, assess earthquake impacts and hazards and perform research into the causes and effects of earthquakes. Gas lines exploded. Power lines fell, telephone service cut. Chimneys toppled. Windows shattered. Dams threatened to burst. And thousands of homes, businesses, hospitals and government agencies were turned upside down. Of the 64 deaths — the estimates vary — nine were attributed to heart attacks.
Despite the ruin, nearly 1, patients and staff were safely evacuated. At least a dozen bridges fell onto freeway lanes, including the overpass at Interstate 5 and the Freeway, killing two. A recently completed Newhall Pass interchange at I-5 and Highway 14 collapsed the same overpass that also failed 23 years later during the 6.
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