Солтүстік Калифорниядағы жер сілкінісі және оның салдары

Major earthquake in northern California

Damage was heavy in Santa Cruz County and less so to the south in Monterey County, but effects extended well to the north into the San Francisco Bay Area, both on the San Francisco Peninsula and across the bay in Oakland. No surface faulting occurred, though many other ground failures and landslides were present, especially in the Summit area of the Santa Cruz Mountains. Liquefaction was also a significant issue, especially in the heavily damaged Marina District of San Francisco, but its effects were also seen in the East Bay, and near the shore of Monterey Bay, where a non destructive tsunami was also observed. Because it happened during a national live broadcast of the 1989 World Series, the annual championship series of Major League Baseball, taking place between Bay Area teams San Francisco Giants and the Oakland Athletics, it is sometimes referred to as the "World Series earthquake", with the championship games of the year being referred to as the "Earthquake Series". Rush hour traffic on the Bay Area freeways was lighter than normal because the game, being played at Candlestick Park in San Francisco, was about to begin, and this may have prevented a larger loss of life, as several of the Bay Area's major transportation structures suffered catastrophic failures. The collapse of a section of the double deck Nimitz Freeway in Oakland was the site of the largest number of casualties for the event, but the collapse of human made structures and other related accidents contributed to casualties occurring in San Francisco, Los Altos, and Santa Cruz.

The history of earthquake investigations in California has been largely focused on the San Andreas Fault system because of its strong influence in the state as the boundary between the Pacific Plate and the North American Plate; it is the most studied fault on Earth. Andrew Lawson, a geologist from the University of California, Berkeley, had named the fault after the San Andreas Lake (prior to the occurrence of the 1906 San Francisco earthquake) and later led an investigation into that event. The San Andreas Fault ruptured for a length of 290 mile (467 km) during the 1906 shock, both to the north of San Francisco and to the south in the Santa Cruz Mountains region. Several long term forecasts for a large shock along the San Andreas Fault in that area had been made public prior to 1989 (the event and its aftershocks occurred within a recognized seismic gap) but the earthquake that transpired was not what had been anticipated. The 1989 Loma Prieta event originated on an undiscovered oblique slip reverse fault that is located adjacent to the San Andreas Fault.

Since many forecasts had been presented for the region near Loma Prieta, seismologists were not taken by surprise by the October 1989 event. Between 1910 and 1989 there were 20 widely varying forecasts that were announced, with some that were highly specific, covering multiple aspects of an event, while others were less complete and vague. With a M6.5 event on the San Juan Bautista segment, or an M7 event on the San Francisco Peninsula segment, United States Geological Survey (USGS) seismologist Allan Lindh's 1983 forecasted rupture length of (starting near Pajaro Gap, and continuing to the northwest) for the San Juan Bautista segment nearly matched the actual rupture length of the 1989 event. An updated forecast was presented in 1988, at which time Lindh took the opportunity to assign a new name to the San Juan Bautista segment – the Loma Prieta segment. In early 1988, the Working Group for California Earthquake Probabilities (WGCEP) made several statements regarding their forecasts for the 225 mile (362 km) northern San Andreas Fault segment, the 56 mile (90 km) San Francisco Peninsula segment, and a portion of that segment which was referred to as the southern Santa Cruz Mountains segment. The thirty year probability for one or more M7 earthquakes in the study area was given as 50%, but because of a lack of information and low confidence, a 30% probability was assigned to the Southern Santa Cruz Mountains segment. Two moderate shocks, referred to as the Lake Elsman earthquakes by the USGS, occurred in the Santa Cruz Mountains region in June 1988 and again in August 1989. Following each event, the State office of Emergency Services issued (for the first time in Bay Area history) short term advisories for a possible large earthquake, which meant there was "a slightly increased likelihood of an M6.5 event on the Santa Cruz Mountains segment of the San Andreas fault". The advisories following the two Lake Elsman events were issued in part because of the statements made by WGCEP and because they were two of the three largest shocks to occur along the 1906 earthquake's rupture zone since 1914. The June 27, 1988, shock occurred with a maximum intensity of VI (Strong). Its effects included broken windows in Los Gatos, and other light damage in Holy City, where increased flow was observed at a water well. Farther away from the Santa Cruz Mountains, pieces of concrete fell from a parking structure at the Sunnyvale Town Center, a two level shopping mall in Santa Clara County. More moderate damage resulted from the August 8, 1989, shock (intensity VII, Very strong) when chimneys were toppled in Cupertino, Los Gatos, and Redwood Estates. Other damage included cracked walls and foundations and broken underground pipes. At the office of the Los Gatos City Manager, a window that was cracked had also been broken in the earlier shock. Also in Los Gatos, one man died when he fell or jumped through a window and impacted the ground five stories below.

The Loma Prieta earthquake was named for Loma Prieta Peak in the Santa Cruz Mountains, which lies just to the east of the mainshock epicenter. The duration of the heaviest shaking in the Santa Cruz Mountains was about 15 seconds, but strong ground motion recordings revealed that the duration of shaking was not uniform throughout the affected area (because of different types and thicknesses of soil). At sites with rocky terrain, the duration was shorter and the shaking was much less intense, and at locations with unconsolidated soil (like the Marina District in San Francisco or the Cypress Street Viaduct in Oakland) the intensity of the shaking was more severe and lasted longer. The strong motion records also allowed for the causative fault to be determined – the rupture was related to the San Andreas Fault System. The contrasting characteristics of the 1906 and 1989 events were examined by seismologists Hiroo Kanamori and Kenji Satake. The significant amount of vertical displacement in 1989 was a key aspect to consider because a long term sequence of 1989 type events (with an 80–100 year recurrence interval) normally result in regions with high topographic relief, which is not seen in the Santa Cruz Mountains. Three scenarios were presented that might explain this disparity. The first is that the geometry of the San Andreas Fault goes through a transition every several thousand years. Secondly, slip type could vary from event to event. And lastly, the 1989 event did not occur on the San Andreas Fault.

While the effects of a four year drought limited the potential of landslides, the steep terrain near the epicenter was prone to movement, and up to 4,000 landslides may have occurred during the event. The majority of landslides occurred to the southwest of the epicenter, especially along road cuts in the Santa Cruz Mountains and in the Summit Road area, but also along the bluffs of the Pacific Coast, and as far north as the Marin Peninsula. Highway 17 was blocked for several weeks by a large slide and one person was killed by a rockfall along the coast. Other areas with certain soil conditions were susceptible to site amplification due to the effects of liquefaction, especially near the shore of San Francisco Bay (where its effects were severe in the Marina District) and to the west of the epicenter near rivers and other bodies of water. Minor lateral spreading was also seen along the shores of San Francisco Bay and to the south near Monterey Bay. Other ground effects included downslope movement, slumps, and ground cracks.

Fifty seven of the deaths were directly caused by the earthquake; six further fatalities were ruled to have been caused indirectly. In addition, there were 3,757 injuries as a result of the earthquake, 400 of which were serious. The highest number of deaths, 42, occurred in Oakland because of the collapse of the Cypress Street Viaduct on the Nimitz Freeway (Interstate 880), where the upper level of a double deck portion of the freeway collapsed, crushing the cars on the lower level, and causing crashes on the upper level. One 50 feet (15 m) section of the San Francisco–Oakland Bay Bridge also collapsed, leading to a single fatality, Anamafi Moala, a 23 year old woman. Three people were killed in the collapse of buildings along the Pacific Garden Mall in Santa Cruz, and five people were killed in the collapse of a brick wall on Bluxome Street in San Francisco. When the earthquake hit, the third game of the 1989 World Series baseball championship was about to begin. Because of the unusual circumstance that both of the World Series teams (the San Francisco Giants and Oakland Athletics) were based in the affected area, many people had left work early or were staying late to participate in after work group viewings and parties. As a consequence the normally crowded freeways contained unusually light traffic. If traffic had been normal for a Tuesday rush hour, injuries and deaths would certainly have been higher. The initial media reports failed to take into account the game's effect on traffic and initially estimated the death toll at 300, a number that was corrected to 63 in the days after the earthquake.

After the earthquake occurred, a group led by Antony C. Fraser Smith of Stanford University reported that the event was preceded by disturbances in background magnetic field noise as measured by a sensor placed in Corralitos, about 4.5 mile (7 km) from the epicenter. The Fraser Smith et al. report remains one of the most frequently cited claims of a specific earthquake precursor; more recent studies have cast doubt on the connection, attributing the Corralitos signals to either unrelated magnetic disturbance or, even more simply, to sensor system malfunction.

The earthquake caused severe damage in some very specific locations in the Bay Area, most notably on unstable soil in San Francisco and Oakland. Oakland City Hall was evacuated after the earthquake until a US$80 million (equivalent to US$80.0 in 1989 is equivalent to about <calculated amount> in recent years million today) seismic retrofit and hazard abatement work was completed in 1995. Many other communities sustained severe damage throughout the region located in Alameda, San Mateo, Santa Clara, San Benito, Santa Cruz and Monterey counties. Major property damage in San Francisco's Marina District 60 mile (97 km) from the epicenter resulted from liquefaction of soil used to create waterfront land. Other effects included sand volcanoes, landslides and ground ruptures. Some 12,000 homes and 2,600 businesses were damaged. In Santa Cruz, close to the epicenter, 40 buildings collapsed, killing six people. At the Santa Cruz Beach Boardwalk, the Plunge Building was significantly damaged. Liquefaction also caused damage in the Watsonville area. For example, sand volcanoes formed in a field near Pajaro as well as in a strawberry field. In the Old Town historical district of the city of Salinas, unreinforced masonry buildings were partially destroyed. Following the quake, an estimated 1.4 million people experienced power losses that were mainly due to damaged electrical substations. Many San Francisco radio and television stations were temporarily knocked off the air. KGO TV, the local ABC station in San Francisco, was off the air for about 15 minutes, while KRON TV (at the time the region's NBC affiliate) was off the air for about half an hour, KCBS AM (CBS News Radio) switched immediately to backup power and managed to stay on air despite a subsequent generator failure. KNBR AM (the designated station for the Bay Area's Emergency Broadcast System at the time) failed to communicate a catastrophe with the activation and instructions of the Emergency Broadcast System to the public after the quake because the engineering department at KNBR experienced major technical malfunctions and difficulties. The malfunctions during the aftermath of the earthquake caused confusion as to whether an earthquake would cause the Emergency Broadcast System to activate. KNBR began using an emergency generator, hooking up the signal from a command center right after their nearby studio was severely shaken during the quake, when most of the KNBR staff were at Candlestick for the World Series. The Mayor of San Francisco, Art Agnos, later came on the air and provided an update on the earthquake. (All four network affiliated TV stations (KRON, KGO, KTVU and CBS affiliate KPIX) would recover enough to broadcast continuous breaking news coverage of the aftermath of the quake for the next several hours, some of it picked up and broadcast nationally over their respective networks, as well as on CNN, in a manner anticipating later major catastrophes such as the 1994 Los Angeles earthquake and the 9/11 terror attacks). Power was restored to most of San Francisco by midnight, and all but 12,000 customers had their power restored within two days.

Four people died in San Francisco's Marina District, four buildings were destroyed by fire, and seven buildings collapsed. Another 63 damaged structures were judged too dangerous to live in. Among the four deaths, one family lost their infant son who choked on dust while trapped for an hour inside their collapsed apartment. After the Exposition, apartment buildings were erected on the landfill. In the 1989 earthquake, the water saturated unconsolidated mud, sand, and rubble suffered liquefaction, and the earthquake's vertical shock waves rippled the ground more severely. At the intersection of Beach and Divisadero Streets in San Francisco, a natural gas main rupture caused a major structure fire. The San Francisco Fire Department selected civilians to help run fire hoses from a distance because the nearby hydrant system failed. Since the bay was only two blocks from the burning buildings, The apartment structures that collapsed were older buildings that included ground floor garages, which engineers refer to as a soft story building.

In Santa Cruz, the Pacific Garden Mall was severely damaged, with falling debris killing three people, half of the six earthquake deaths in Santa Cruz and Monterey Counties. Some 31 buildings were damaged enough to warrant demolition, seven of which had been listed in the Santa Cruz Historic Building Survey. The four oldest were built in 1894, the five oldest withstood the 1906 San Francisco earthquake. The civilians who were helpful initially, were soon viewed by police and fire officials as a hindrance to operations, with frantic coworkers and friends of a coffee house employee thought to be trapped under the rubble continuing their efforts in the dark. Police arrested those who refused to stop searching. This became a political issue in the following days. The body of a young woman coffee worker was found under a collapsed wall late the next day. During the first few days following the quake, electric power to most Santa Cruz County subscribers was out, and some areas had no water. Limited phone service remained online, providing a crucial link to rescue workers. In other Santa Cruz and Monterey county locations such as Boulder Creek and Moss Landing, a number of structures were damaged, with some knocked off of their foundations. Damage to the Salinas River rail bridge and subsequent repairs led to reduced traffic on the Monterey Branch Line, which contributed to the discontinuance of freight rail services in western Monterey County.

The San Francisco–Oakland Bay Bridge suffered severe damage, as a section of the upper deck on the eastern cantilever side fell onto the deck below. The quake caused the Oakland side of the bridge to shift to the east, and caused the bolts of one section to shear off, sending the section of roadbed crashing down like a trapdoor. Traffic on both decks came to a halt, blocked by the section of the roadbed. Police began unsnarling the traffic jam, telling drivers to turn their cars around and drive back the way they had come. Eastbound drivers stuck on the lower deck between the collapse and Yerba Buena Island were routed up to the upper deck and westward back to San Francisco. A miscommunication made by emergency workers at Yerba Buena Island routed some drivers the wrong way; they were directed to the upper deck where they drove eastward toward the collapse site. Caltrans removed and replaced the collapsed section, and re opened the bridge on November 18. Built in the late 1950s and opened to traffic in 1957 (as SR 17), the Cypress Street Viaduct, a stretch of Interstate 880, was a double deck freeway section made of nonductile reinforced concrete that was constructed above and astride Cypress Street in Oakland. Roughly half of the land the Cypress Viaduct was built on filled marshland and half on somewhat more stable alluvium. Because of new highway structure design guidelines – the requirement of ductile construction elements – instituted following the 1971 San Fernando earthquake, a limited degree of earthquake reinforcement was retrofitted to the Cypress Viaduct in 1977. The added elements were longitudinal restraints at transverse expansion joints in the box girder spans, but no studies were made of possible failure modes specific to the Cypress Viaduct. Caltrans has since received widespread backlash for not thoroughly studying the structure. Employees from Pacific Pipe drove heavy lift equipment to the scene and started using it to raise sections of fallen freeway enough to allow further rescue. Local workers continued their volunteer operation nonstop until October 21, 1989, when they were forced to pause as U. S. President George H. W. Bush and California Governor George Deukmejian viewed the damage. That same day, survivor Buck Helm was freed from the wreckage, having spent 90 hours trapped in his car. Dubbed "Lucky Buck" by the local radio, Helm lived for another 29 days on life support, but then died of respiratory failure at the age of 58. Although the freeway reopened in stages between 1997 and 1999, it was not fully rebuilt until 2001 so that it would comply with safety and reinforcement standards. In the meantime, traffic was detoured through nearby Interstate 980, causing increased congestion.

Aftershocks Mag Date (UTC) Year 4.3 Oct 18 at 00:38 1989 5.2 Oct 18 at 00:41 1989 4.0 Oct 18 at 02:26 1989 4.1 Oct 18 at 03:30 1989 4.2 Oct 18 at 04:50 1989 4.2 Oct 18 at 05:18 1989 4.3 Oct 18 at 10:22 1989 4.3 Oct 19 at 9:53 1989 4.2 Oct 21 at 10:22 1989 4.7 Oct 21 at 22:14 1989 4.3 Nov 2 at 05:50 1989 4.3 Apr 18 at 13:37 1990 4.5 Apr 18 at 13:41 1990 5.4 Apr 18 at 13:53 1990 4.2 Apr 18 at 14:52 1990 4.2 Apr 18 at 15:28 1990 4.5 Mar 24 at 03:42 1991

Immediately after the earthquake, Bay Area airports were closed so officials could conduct a visual inspection and damage assessment procedures. San Jose International Airport, Oakland International Airport and San Francisco International Airport all opened the next morning. Large cracks in Oakland's runway and taxiway reduced the usable length to two thirds normal, and damage to the dike required quick remediation to avoid flooding the runway with water from the bay. Oakland Airport repair costs were assessed at $30 million (equivalent to $30.0 in 1988 is equivalent to about <calculated amount> in recent years million today). San Francisco Municipal Railway (Muni) lost all power to electric transit systems when the quake hit, but otherwise suffered little damage and no injuries to operators or riders. Cable cars and electric trains and buses were stalled in place – half of Muni's transport capability was lost for 12 hours. Muni relied on diesel buses to continue abbreviated service until electric power was restored later that night, and electric units could be inspected and readied for service on the morning of October 18. The earthquake changed the Bay Area's automobile transportation landscape. Not only did the quake force seismic retrofitting of all Bay Area bridges, it caused enough damage that some parts of the region's freeway system had to be demolished. Damage to the region's transportation system was estimated at $1.8 billion (equivalent to $1.8 in 1989 is equivalent to about <calculated amount> in recent years billion today). San Francisco–Oakland Bay Bridge, Interstate 80: The Bay Bridge was repaired and reopened to traffic in a month. 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 began on January 29, 2002. The project was completed on September 2, 2013. Cypress Street Viaduct/Nimitz Freeway, Interstate 880: The 1.78 mile (3 km) double decked Cypress Street Viaduct, Interstate 880 was demolished soon after the earthquake and was not replaced until July 1997 (To the Bay Bridge only, the ramps to and from Interstate 80 east were not completed until 2001 despite opening in 1999). The replacement freeway section is a single deck rather than double deck structure and was re routed around the outskirts of West Oakland, rather than bisecting it as the Cypress Street Viaduct had done. The former route of the Cypress Street Viaduct was reopened as the ground level Mandela Parkway. Embarcadero Freeway, State Route 480: Earthquake damage forced the closure and demolition of San Francisco's incomplete and controversial Embarcadero Freeway (State Route 480). This removal opened up San Francisco's Embarcadero area to new development. The elevated structure, which ran along San Francisco's waterfront, was demolished in 1991 and later replaced with a ground level boulevard. 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 uncompleted northernmost stub of I 280 was demolished during August–October 1995 while one connecting ramp between northbound I 280 and southbound US 101 was opened in December 1995. The full I 280 project was completed in late 1997. In addition, another segment of Interstate 280 in Los Altos near State Route 85 also suffered seismic damage and was subsequently repaired. Central Freeway, U. S. Highway 101: San Francisco's Central Freeway (part of US 101 and a key link to the Bay Bridge flyover) was another concrete double deck structure that faced demolition because of safety concerns. Originally terminating at Franklin Street and Golden Gate Avenue 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). State Route 17: Over half of the 26 mile (42 km) highway was closed for about one to two months because of landslides that occurred between Granite Creek Road in Scotts Valley and State Route 9 in Los Gatos (only Buses and carpoolers with three or more people could cross it). After reopening, retaining walls and barbed fences were added in damaged areas to prevent any further landslides/rockslides. The route crosses the San Andreas Fault in the Santa Cruz Mountains, near the earthquake's epicenter. Cabrillo Highway, State Route 1: In Watsonville, the Struve Slough Bridge collapsed, with concrete/steel support columns penetrating up through the bridge deck. The highway was closed for several months until it could be demolished and rebuilt (commuters took SR 152 and SR 129 as bypass routes). Another section of Highway 1 through Monterey suffered damage and had to be rebuilt as well. Additionally, the bridge carrying Highway 1 over the Salinas River near Highway 156 and Fort Ord was damaged and subsequently 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. With the Bay Bridge closed because of its damage, the Transbay Tube became the quickest way into San Francisco via Oakland for a month, and ridership increased in the three work weeks following the earthquake, going from 218,000 riders per average weekday to more than 330,000 post quake, a 50% increase. Amtrak: Historic 16th Street Station in downtown Oakland suffered significant damage and was rendered structurally unsound. Amtrak would shift its Oakland operations to a new station in Emeryville. 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. A ferry terminal was put together in Alameda, and the U. S. Army Corps of Engineers dredged a suitable ferry dock at the Berkeley Marina. Additionally, the demolition of the quake damaged Embarcadero Freeway led to the Ferry Building Terminal renovation, increasing the efficiency of ferry service to the peninsula. The passenger only service proved popular and continues to expand its service. The need for a robust ferry system in the event that the region's roads and tunnels become impassable in an emergency led to the creation of the San Francisco Bay Ferry system.