Loma Prieta earthquake
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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 7.1 on the Richter magnitude scale (6.9 on the Moment magnitude scale). It is popularly nicknamed the World Series Quake because it occurred during the World Series, which happened to match up the Bay Area's two Major League Baseball teams. The earthquake lasted for 15 seconds. Its epicenter was at geographical coordinates near Loma Prieta Peak in the Santa Cruz Mountains, about ten miles (16 km) northeast of the city of Santa Cruz, California, in the Forest of Nisene Marks State Park. The focus point was at a depth of 16.79 km, or 10 miles.
This was a major earthquake which caused severe damage as far as 70 miles (110 km) away; 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 at least 63 deaths (some say 66) and 3,757 injuries as a result of this earthquake. The highest concentration of fatalities, 42, occurred in the collapse of the Cypress Street Viaduct 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.
After the 1906 earthquake much of the rubble was bulldozed into San Francisco Bay. This reclaimed land was built upon and was extremely unstable. In the Loma Prieta 'quake many buildings on this reclaimed land were destroyed.
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 Street Viaduct 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 p.m.). 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. Not taking this into account, initial media reports pegged the death toll at 300, a number that was corrected in the days after the earthquake. [link]
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.
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.
The quake also caused an estimated $6 billion in property damage, the costliest natural disaster in U.S. history at the time. It was the largest earthquake to occur on the San Andreas Fault since the great 1906 San Francisco earthquake. Private donations poured in to aid relief efforts and on October 26, President Bush signed a $3.45 billion earthquake relief package for California.
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.- San Francisco-Oakland Bay Bridge, Interstate 80: The Bay Bridge was repaired and reopened to traffic in just one month's time. However, the earthquake made it clear that the Bay Bridge, like many of California's toll bridges, required major repair or replacement, for long-term viability and safety. Construction on a replacement for the eastern span would not begin, however, until January 29, 2002. As of 2005, news accounts estimate that the project will not be completed by 2011 due to the California budget crisis. (For discussion, see also San Francisco-Oakland Bay Bridge).
- Cypress Street Viaduct/Nimitz Freeway, Interstate 880: The double-decked Cypress Street Viaduct, Interstate 880 was demolished soon after the earthquake, and was not rebuilt until July 1997. The rebuilt highway was a single- rather than double-decker structure, and was re-routed around the outskirts of West Oakland, rather than bisecting it, as the Cypress Street Viaduct did. The former route of the Cypress Street Viaduct was reopened as the Mandela Parkway.
- Embarcadero Freeway, Interstate 480: The earthquake forced the closure and demolition of San Francisco's largely unloved Embarcadero Freeway (Interstate 480); this demolition opened up San Francisco's Embarcadero waterfront to new development. The concrete freeway, which ran right along San Francisco's waterfront and had never been completed, was replaced with a ground-level boulevard.
- Southern Freeway, Interstate 280: Seismic damage also forced the long-term closure of Interstate 280 in San Francisco (north of US-101), another concrete freeway which had never been completed to its originally planned route. The highway remained closed for seven years, with its repair facing numerous delays.
- Central Freeway, U.S. Route 101: San Francisco's Central Freeway (part of US 101 and a key link to the Bay Bridge skyway) was another concrete double-deck structure which faced demolition due to safety concerns. Originally terminating at Franklin Street near San Francisco's Civic Center, the section past Fell Street was demolished first, then later the section between Mission and Fell Streets. The section from Mission Street to Market Street was rebuilt (completed September 2005) as a single-deck elevated freeway, touching down at Market Street and feeding into Octavia Boulevard, a ground-level urban parkway carrying traffic to and from the major San Francisco traffic arterials that the old elevated freeway used to connect to directly, including Fell and Oak Streets (which serve the city's western neighborhoods) and Franklin and Gough Streets (which serve northern neighborhoods and the Golden Gate Bridge).
- Highway 17, California State Route 17: The mountain highway was closed for about 1 month due to landslide. The highway is very close to the epicenter and it crosses the San Andreas Fault.
- Highway 1: In Watsonville, the Struve Slough bridge collapsed on itself with concrete/steel support columns punching through the bridge deck like toothpicks. The highway was closed for several months until it could be demolished and rebuilt.
- Bay Area Rapid Transit: The BART rail system, which hauled commuters between the East Bay and San Francisco via the Transbay Tube, was virtually undamaged and only closed for post-earthquake inspection. As one of the few ways into San Francisco in the days following the earthquake, ridership increased by 90,000 in the week after the earthquake (from 218,000 to 308,000).
- Transbay Ferries: Ferry service between San Francisco and Oakland, which had ended decades before, was revived during the month-long closure of the Bay Bridge as an alternative to the overcrowded BART. Alameda was a third terminal. The passenger-only service proved popular and still continues as of 2006, with a more recent extension to Vallejo on San Pablo Bay.
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 been shown on live television. KGO-TV was the first to cover the earthquake after the game was canceledFortunately, less 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.
ABC sportscaster Al Michaels was nominated for an Emmy award for his news broadcasts about the earthquake.
Scientific precursors
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 October 13 1989.Berkland bases his predictions on anomalies in tidal information, gravitational data, animal behavior, and other unproven sources. Cal Orey, The Man Who Predicts Earthquakes: Jim Berkland, Maverick Geologist--How His Quake Warnings Can Save Lives, (Sentient Publications), ISBN 1591810361. His theories and methods are controversial, and are considered unreliable by mainstream scientists.
External links
Seismology
- [USGS: Loma Prietos]
- *[Simulation of Mercalli Scale ground motion presented as a 75 second animation] (Low-Res Quicktime)
- *[Simulation of Mercalli Scale ground motion presented as a 75 second animation] (High-Res Quicktime)
- [USGS list of additional Loma Prieta sites]
- [Selected USGS photographs from the Loma Prieta earthquake]
- [Progress Toward a safer future since the 1989 Loma Prieta Earthquake]
- [Additional information on the Loma Prieta Earthquake]
- [Prof. Antony C. Fraser-Smith, low-frequency electromagnetic precursors to earthquakes]
Transportation
- [15 Seconds That Changed San Francisco], San Francisco Chronicle, October 17, 2004. Overview with photographs; analysis of changes between 1989 and 2004.
Notes
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