Loma Prieta earthquake

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The Loma Prieta earthquake occurred on Tuesday 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 37.04° N 121.88° W 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.

Contents 1 Science, effects and response 2 Elaboration of Significant Events 3 Transportation effects 4 1989 World Series 5 Scientific precursors 5.1 Magnetic disturbances 5.2 Geological data anomalies 6 External links 6.1 Seismology 6.2 Transportation 6.3 Images 7 Notes

[edit] 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^[1]. In addition, there were 3,757 injuries as a result of the earthquake. The highest concentration of fatalities, 40, 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, along with traffic levels on nearby bridges such as the Richmond-San Rafael and the Golden Gate.

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 earthquake 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. [1]

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 George H.W. Bush signed a $3.45 billion earthquake relief package for California.

[edit] Elaboration of Significant Events

The San Francisco-Oakland Bay Bridge suffered relatively minor damage, as a 50-foot (15 meter) section of the upper deck on the eastern side crashed onto the deck below. The quake caused the oakland side of the bridge to shift eighteen centimeters to the east, and caused the bolts of one section to shear off, sending the small part of the roadbed crashing down like a trapdoor. When that part of the bridge collapsed, a few motorists fell into the hole, but landed safely on the lower deck, preventing them from falling into the bay. Allegedly, a miscommunication made by the police directed some of the drivers on the bridge in the wrong direction; instead of driving away from the collapse site, they were directed toward the collapse site. Anamafi Moala Kalushia, driving her brother on the bridge, approached the collapse site too quickly to stop, and drove the car off the ledge and smashed onto the fallen roadbed. Her brother was pulled to safety and eventually recovered from his serious injuries. Anamafi, unfortunately, died shortly after plunging off the upper deck. She was the only fatality on the bridge. On November 18, almost exactly one month after the earthquake, the fallen section was removed and replaced, and the bridge was re-opened

.

In San Francisco's Marina District, several apartment buildings and other multi-story homes were damaged heavily. Because the land the Marina neighborhood sat on was filled land, the earthquake's shockwaves rippled the ground with more severity. As the mixture of sand, dirt, rubble, and other materials used to make up the artificial ground mixed with the water underneath, multi-story buildings literally sank into the ground. Four-to-five story apartment buildings collapsed "like houses of cards" as the first stories gave way and sent the upper floors crashing down. In some instances, only the top floor was left intact, having spilled into the road, crushing parked cars, trees, and light poles.

At the intersection of San Francisco's Beach and Divisadero Streets, there was a major structure fire, due to a gas main rupture. Bystanders were selected by the fire deparment to help run fire hoses to the scene, which had to be connected at a distance because the hydrant system failed. Water from the bay was shot at the burning buildings by fire boats, similar to those used to put out fires caused by the 1906 earthquake.

In collapsed buildings that did not catch fire, rescue teams searched the fallen buildings thoroughly, pulling out various survivors from underneath splintered wood and other debris. Most of the apartment structures that collapsed were corner units, with garage doors lined up on the exposed corners. Not originally part of the buildings, the garage doors that were installed quite some time after the buildings' initial construction weakened the first-story walls, causing the stiff, wood-frame buildings to buckle, crack, and crash into the streets. There were about five deaths that occurred from Marina District apartment fires and collapses. One family lost their baby boy in the earthquake who was trapped underneath the upper stories of their apartment that fell on the lower ones.

In Santa Cruz, the Pacific Garden Mall was irrepairably damaged, killing three people. Brick facades poured into the streets, buildings self-destructed themselves by butting up against one another, and the historic streets of Santa Cruz were filled with debris, rescue workers, and concerned evacuees.

By far, the worst disaster of the earthquake was the collapse of the Cypress Viaduct in west Oakland, right across the bay from San Francisco. In a strange twist of events, traffic was significantly light as most Bay Area fans had either flocked to game three of the 1989 World Series or to their homes to watch the game on television. As a result, rush-hour traffic was surprisingly minimal.

Built in the late 1950s, the Cypress Viaduct (a small stretch of the I-880 Nimitiz Freeway) was a double-decker freeway system that was relatively innovative when it was first constructed.

Because little attention had been paid to strengthening it in case of a major earthquake, the freeway was changed very little from when it was built. Like the Marina District, the land the Cypress Viaduct was built on was simply filled marshland. When the earthquake hit, the shaking was amplified in those areas, causing more damage than would have normally occurred if the land was bedrock. With the combination of outdated earthquake standards and unstable ground, the freeway buckled and twisted to the limits before the support columns failed and sent the upper deck crashing to the bottom deck. In an instant, over forty people were crushed in their cars, with nowhere to go when the earthquake hit. Appearing as though a "bomb had been exploded on the structure," the gigantic freeway was in ruins, with chunks of concrete in the streets below, steel rebar twisting out, cars on the upper deck thrown around, and thick smoke coming out from in between the pancaked roadbeds. Nearby residents came to the rescue, bravely climbing onto the wreckage and pulling trapped people out of their mangled cars. There was about a four-foot space between the upper and lower decks.

According to engineers, the structure's weak support columns were not designed to withstand a large amount of movement. As a result, the columns exploded outward, thrusting the upper deck onto the one below. Cars on the lower deck were crushed "like beer cans," some of them being flattened to their axels. Cars on the upper deck were tossed around violently, some of them flipped sideways and some of them dangling near the edge of the highway. Cranes were used to retrieve the cars from the upper deck. Paramedics pulled the crushed victims out of their mutilated cars. In total, 40 people died in this incident. The street-level Mandela Parkway stands where the deadly freeway once stood.

[edit] 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).
• 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.
• California State Route 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.

[edit] 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 Tim McCarver was narrating taped highlights of the previous Series game. Viewers saw the video signal begin to break up, and heard McCarver's colleague, Al 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 (who had worked as a broadcaster for the San Francisco Giants earlier in his career), 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.

See also: Major League Baseball on ABC

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.

[edit] Scientific precursors

[edit] 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 3, rising to 60 times normal about three hours before the earthquake.

[edit] 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. ^[2] His theories and methods are controversial, and are considered unreliable by mainstream scientists.

[edit] External links

[edit] Seismology

• USGS: Loma Prieta
  • 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

[edit] Transportation

• 15 Seconds That Changed San Francisco, San Francisco Chronicle, October 17, 2004. Overview with photographs; analysis of changes between 1989 and 2004.

[edit] Images

• KPIX-TV San Francisco live coverage of 1989 Loma Prieta Earthquake

[edit] Notes