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The Loma Prieta earthquake occurred on October 17, 1989, in the greater San Francisco Bay Area in California at 5:04 p.m. local time and measured 6.9 on the Moment magnitude scale (surface-wave magnitude 7.1). It occurred during the 1989 World Series, which happened to match up the Bay Area's two Major League Baseball teams, the Oakland Athletics against the San Francisco Giants. The earthquake lasted for 15 seconds. Its epicenter was at geographical coordinates south-southwest of Loma Prieta Peak in the unincorporated area of Aptos. This location, in the Santa Cruz Mountains' Forest of Nisene Marks State Park, is about ten miles (16 km) northeast of the city of Santa Cruz, California. The focus point was at a depth of 16.79 km, or 10 miles. The Loma Prieta was a major earthquake, and caused severe damage as far as 50 miles away from its epicenter; most notably in San Francisco, Oakland, the San Francisco Peninsula, and in areas closer to the epicenter in the communities of Santa Cruz, the Monterey Bay, Watsonville, and Los Gatos. Most of the major property damage in the more distant areas resulted from liquefaction of soil used over the years to fill in the waterfront and then built upon.
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 15 miles) discontinuities in the Earth's gross structure. There were 57 deaths directly caused by the earthquake, and six more deaths were ruled to be indirectly caused by the temblor• Transportation effects The Loma Prieta earthquake irrevocably changed the San Francisco Bay Area's transportation landscape. Not only did the quake force seismic retrofitting of all San Francisco Bay Area bridges, it caused enough damage that some parts of the region's freeway system had to be demolished. In some cases, the freeways in question had never been completed, terminating in mid-air; in that regard, the quake provided the impetus to deal with regional transportation problems that had gone largely unsolved for decades. 1989 World Series The earthquake had been "predicted" in the morning edition of The San Jose Mercury News in a column by Kevin Cowherd (of The Baltimore Sun). He was discussing the fact that the Oakland Athletics and the San Francisco Giants were playing each other in the 1989 World Series at Candlestick Park that day. The quote from his column read: "... these are two teams from California and God only knows if they'll even get all the games in. An earthquake could rip through the Bay Area before they sing the national anthem for Game 3,"— which was precisely when the quake occurred. It is one of the few times that the onset of an earthquake of such magnitude had occurred during a live network television broadcast. The Series was being broadcast that year by U.S. television network ABC. At the moment the quake struck, sportscaster Al Michaels was narrating taped highlights of the previous Series game. Viewers saw the video signal begin to break up, and heard Michaels exclaim, "I'll tell you what -- we're having an earth--." At that moment the feed from Candlestick Park was lost. It was restored shortly thereafter and for a time Michaels (a native of the Bay Area), by virtue of his presence on the scene and the already existing video link, was ABC's main contact from San Francisco, feeding reports and commentary to anchorman Ted Koppel (in Washington D.C.) Michaels was later nominated for an Emmy Award for these news broadcasts. Fortunately, fewer than half of the 65,000+ fans had reached their seats, lessening the load on the structure of the stadium. There had also been a seismic strengthening project previously completed on the upper deck concrete windscreen. Fans reported that the stadium moved in an articulated manner as the earthquake wave passed through it, that the light standards swayed by many feet, and that the concrete upper deck windscreen moved in a wave-like manner over a distance of several feet. As soon as the shaking stopped, the assembled crowd, unaware of the tragic destruction just beginning to be revealed around the rest of the Bay Area, roared as loud as if a game-winning double had been hit. A few minutes later they yelled "Play Ball, Play Ball!" However, the game was called and the Series was postponed for 10 days. During this time, many Bay Area residents felt the Series should be canceled altogether out of respect for the lives lost and damage sustained, but the World Series was resumed. After the shaking subsided, many of the players for both the Athletics and Giants immediately searched for and gathered family and friends from the stands (while still in full uniform) before evacuating the facility altogether. KGO-TV, the local San Francisco television station of ABC (the national network broadcasting the game) was the first of the local Bay Area television network affiliates to cover the earthquake after the game was canceled (soon afterward, all of the major network stations broadcast continuously for several hours without interruption, providing live news reports and updates). Because of the importance of the World Series as a national sporting event, many members of local, regional and national broadcast media were in attendance and would later broadcast their observations of the aftermath of the earthquake to their viewers. Magnetic disturbances The Loma Prieta earthquake was preceded by significant disturbances in the background magnetic field strength nearby. Large increases in extremely low frequency field strength were observed about 7 kilometers from the epicenter, up to two weeks in advance of the actual event. The measurement instrument was a single-axis search-coil magnetometer that was being used for research on radio communications with submarines by Prof. Antony C. Fraser-Smith of Stanford University. Signal strengths 20 times higher than normal were observed on October 3rd, rising to 60 times normal about three hours before the earthquake. Geological data anomalies A prediction of the Loma Prieta earthquake, by retired geologist Jim Berkland of the U.S. Geological Survey, appeared in a newspaper article four days before the event. The article, entitled "Is 'World Series' Quake Coming?", was published in the Gilroy Dispatch on 13 October 1989. Berkland based his predictions on anomalies in tidal information, gravitational data, animal behavior, and other unproven sources. His theories and methods are controversial, and are considered unreliable by mainstream scientists. Seismology Transportation Images Notes | ||||||||
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