Loma Prieta earthquake

The Loma Prieta earthquake occurred on October 17, 1989 in the greater San Francisco Bay Area in California at 5:04 pm local time and measured 7.1 on the Richter magnitude scale (6.9 on the Moment magnitude scale). The earthquake lasted for fifteen seconds. Its epicenter was at 37.04° N latitude, 121.88° W longitude near Loma Prieta Peak in the Santa Cruz Mountains, about ten miles (16 km) northeast of the town of Santa Cruz, California, in the Forest of Nisene Marks State Park.

Science, Effects and Response

The magnitude and distance of the earthquake from the severe damage to the north were surprising to geotechnologists. Subsequent analysis indicates that the damage was likely due to reflected seismic waves - the reflection from well-known deep (about fifteen miles) discontinuities in the earth's gross structure.

Related Topics:
Seismic - Waves

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There were at least 66 deaths and 3,757 injuries as a result of this earthquake. The highest concentration of fatalities, 42, occurred in the collapse of the Cypress structure on the Nimitz Freeway (Interstate 880), where a double-decker portion of the freeway collapsed, crushing the cars on the lower deck. One 50-foot (15 m) section of the San Francisco-Oakland Bay Bridge also collapsed, causing two cars to fall to the deck below, leading to the single fatality on the bridge. The bridge was closed for repairs for a month and one day, reopening on November 18. While the bridge was closed, ridership on Bay Area Rapid Transit and ferry services soared.

Related Topics:
Interstate 880 - San Francisco-Oakland Bay Bridge - November 18 - Bay Area Rapid Transit

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Because this quake occurred during the evening rush hour, there could have been a large number of cars on the freeways at the time, which on the Cypress structure could have endangered many hundreds of commuters. Very fortunately, and in an unusual convergence of events, the two local major league baseball teams (the Oakland Athletics and the San Francisco Giants) were about to start their third game of the World Series (the game was scheduled to start shortly after 5:30 pm). Many people had left work early or were participating in early after-work group viewings and parties. As a consequence, the usually crowded highways were experiencing exceptionally light traffic at the time.

Related Topics:
Rush hour - Baseball - Oakland Athletics - San Francisco Giants - World Series

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Extensive damage also occurred in San Francisco's Marina District, where many expensive homes built on filled ground collapsed. Fires raged in some sections of the city as water mains broke. San Francisco's fireboat (the Phoenix) was used to pump salt water from San Francisco Bay through hoses dragged through streets by citizen volunteers. Power was cut to most of San Francisco and was not fully restored for several days.

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Deaths in Santa Cruz occurred when brick storefronts and sidewalls in the historic downtown (what was then called the Pacific Garden Mall) tumbled down on people exiting the buildings.

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The quake also caused an estimated $6 billion in property damage, the most costly natural disaster in U.S. history at the time. It was the largest earthquake to occur on the San Andreas Fault since the great San Francisco earthquake in April 1906. Private donations poured in to aid relief efforts and on October 26, President Bush signed a $3.45 billion earthquake relief package for California.

Related Topics:
San Andreas Fault - San Francisco earthquake in April 1906 - October 26 - President Bush

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