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The Northridge Earthquake of 1/17/94, Part II (20 Images)

Set 2: Communities other than Northridge

This presentation is based on a 35mm slide set with the same title published by the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Geophysical Data Center, Boulder, Colorado 80303, USA (Product No. 647-A11-019)

The Earthquake

At 4:31 A.M. (local time) on Monday, January 17, 1994, a magnitude 6.8 earthquake woke nearly everyone in southern California. The earthquake epicenter was beneath the San Fernando Valley, 20 miles (32 km) west-northwest of downtown Los Angeles, near the community of Northridge (34° 13' N, 118°32'W).

The main shock occurred on a shallowly-dipping, previously unknown thrust fault. The rupture started at a depth of about 12 miles (19 km) and, during the course of the main shock, traveled upward and northward, spreading both eastward and westward. The focal mechanism of the main shock from both first motions and teleseisms shows a N 60° W striking and 35° to 45° south dipping plane. Rock on the south side of the fault surged upward and over the rock on the north side. As a result of the quake, the Earth's crust south of the San Fernando Valley moved slightly closer to the Earth's crust north of the valley, and the mountains just north of the valley are slightly higher.

The Damage

Damage was most extensive in the San Fernando Valley, the Simi Valley, and in the northern part of the Los Angeles Basin. After the earthquake, a total of 24,000 dwellings were vacated. The death toll from the quake was 57. The total cost of the earthquake was estimated to be at least $10 billion. The Northridge earthquake is significant since it was the most expensive earthquake and one of the most expensive natural disasters in United States history, yet it occurred on a previously unknown fault.

Damage to building structures outside the epicentral area was severe, spotty in geographic distribution, and spread over a large area. Significant damage was reported as far as Fillmore in the west, Valencia in the north, and Anaheim in the southeast. The distribution of damaged buildings was affected by the type and density of the construction and the strength of the earthquake shaking. It was no surprise that unreinforced masonry and older concrete frame constructions suffered structural damage. However damage and collapses in newer structures - particularly parking garages, commercial buildings, and apartment complexes - were surprising and even alarming, considering the strict compliance with existing building codes.

In the northwestern San Fernando Valley, surface disruptions have been identified. A prominent zone of surface fissures also occurred across Balboa Boulevard in the Granada Hills area. Several pipelines appeared to have pulled apart in approximately the same general area. Generally, the accelerations for this earthquake were higher over a larger area than would have been expected from previous experience with similar-sized earthquakes.

Santa Monica, about 15 miles (24 km) from the epicenter and across the Santa Monica Mountains, was also heavily damaged. Most of the damage occurred in an east-west trending belt within the northern portion of the city, and extended westward into Pacific Palisades and eastward into west Los Angeles and Hollywood. Two hundred million dollars in damage occurred in Santa Monica. One hundred thirtyfour buildings were unsafe for occupancy and 396 others were damaged enough to limit access.

Infrastructure: After the quake occurred, 680,000 people in the Los Angeles area were without power, gas, or phone service. Power outages swept throughout the Los Angeles basin and were reported as far away as Alberta and British Columbia due to the load problems stemming from the quake. Although the phone system survived relatively intact, some long-distance services (into and out of parts of Los Angeles) were lost because of equipment damage and power failure. Water trunk lines were broken, and water surged down some streets; 40,000 people were without water. Gas from a ruptured gas line ignited, and the resulting fire destroyed several homes. Explosions from ruptured gas mains occurred in the midst of the flooding from the broken water mains.

Transportation: The earthquake closed several major highways and freeways. At the Fairfax, La Cienaga, and Venice Boulevard intersection with the Santa Monica Freeway, an overpass fell, closing the nation's busiest freeway. Spans collapsed in the interchange between the Golden State Freeway (I) and the Antelope Valley Freeway (SR-14), in the northern San Fernando Valley. Rock slides closed roads to Malibu Canyon and Topanga Canyon. The highway and freeway collapses nearly isolated some communities and caused commutes of as much as four hours. A Southern Pacific train was derailed near the earthquake epicenter spilling 8,000 gallons of sulfuric acid and 2,000 gallons of diesel fuel.

Hospitals: The most severe damage to health care facilities occurred in the Santa Monica area where a total of five facilities were declared unsafe. The Community Hospital in Granada Hills had to evacuate its top floors and treat people in the parking lot and in debris-strewn hallways. Three hundred people were evacuated from Veterans Administration Medical Center. At the damaged Sepulveda Veterans Administration Hospital, a stream of transit authority buses and private ambulances ferried 330 patients to other facilities. Three people died of quake-related heart attacks at Cedars Sinai Medical Center.