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1990 Luzon earthquake

The 1990 Luzon earthquake occurred on July 16 at 3:26 p.m. (PST) on the densely populated island of Luzon in the Philippines. The shock had a surface-wave magnitude of 7.8 and produced a 125 km-long ground rupture that stretched from Dingalan to Kayapa. The event was a result of strike-slip movements along the Philippine Fault and the Digdig Fault within the Philippine fault system. The earthquake's epicenter was near the town of Rizal, Nueva Ecija, northeast of Cabanatuan. An estimated 1,621 people were killed, most of the fatalities located in Central Luzon and the Cordillera region.

Geology
The Philippine archipelago represents a complex plate boundary between the Philippine Sea and Eurasian plates. To the east, oceanic lithosphere subducts westwards beneath the islands along the Philippine Trench. Off the west coast of Luzon, the Manila Trench accommodates eastward subduction. To its east is the East Luzon Trench, a convergent boundary that separates the Philippine Trench by a transform fault. The left-lateral strike-slip Philippine fault system runs through the islands. It is one of the longest strike-slip faults in the world. Understanding of its geology and earthquake history is limited. It extends north–south for from Mindanao to northern Luzon. On Luzon, the fault branches into multiple splay segments including the northerly trending Digdig Fault. The event was one of the largest continental strike-slip earthquakes of the century. It was associated with a long surface rupture on the Philippine Fault System. Rupture occurred bilaterally, extending from the hypocenter, but most of the rupture occurred northwest for . About north of the epicenter, the largest slip was estimated at . Slip gradually decreased away from the zone. The Digdig Fault displayed of left-lateral displacement. Aftershocks occurred along a length of the fault. They displayed a range of focal mechanism including strike-slip, normal and thrust faulting. ==Impact==
Impact
The earthquake caused damage within an area of about 20,000 square kilometers, stretching from the mountains of the Cordillera Administrative Region and through the Central Luzon region. The earthquake was strongly felt in Metropolitan Manila, destroying many buildings and leading to panic and stampedes and ultimately three deaths in the National Capital Region, one of the lowest fatalities recorded in the wake of the tremor. The ceiling of a movie theater in Pasay reportedly collapsed pinning a number of moviegoers. The Southern Tagalog (nowadays Region 4A (Calabarzon), Mimaropa, and Aurora of Central Luzon) and Bicol Regions also felt the quake, but with low casualty figures. Then-president Cory Aquino, who was having a meeting with Senate leaders at Malacañang Palace in Manila, recounted that she hid under a long conference table during the earthquake. She later ordered the suspension of classes and the mobilization of relief agencies. The quake destroyed electric, water and communication lines in the city. The main vehicular route to Baguio, Kennon Road, as well as other access routes to the mountain city, were shut down due to landslides and it took three days before enough landslide debris was cleared to allow access by road to the stricken city. Among the first rescuers to arrive at the devastated city were miners from Benguet Corporation, who focused on rescue efforts at the collapsed Hotel Nevada. Then Major Danilo A. Aquino of the Philippine Military Academy, was the ground commander under the supervision of General Arturo Enrile, mobilized cadet volunteers from day 1 of the rescue mission until the last day of the recovery mission. Miners hailed the Cadets as heroes for their act of bravery for staying in the buildings despite strong after shocks. A number of cadets were awarded the Bronze Cross for their heroic efforts. Teams sent by the Philippine government and by foreign governments and agencies likewise participated in the rescue and retrieval operations in Baguio. One of the more prominent buildings destroyed was the Hyatt Terraces Baguio Hotel, where at least eighty hotel employees and guests were killed, including at least four employees of the state-owned Philippine Amusement and Gaming Corporation which ran the casino. Three hotel employees, however, were pulled out alive after having been buried under the rubble for nearly two weeks, and after international rescue teams had abandoned the site convinced there were no more survivors. Luisa Mallorca and Arnel Calabia were extricated from the rubble 11 days after the quake, while hotel cook Pedrito Dy was recovered alive 14 days following the earthquake. All three survived in part by drinking their own urine Cabanatuan In Cabanatuan, Nueva Ecija, the tallest building in the city, a six-story concrete school building housing the Christian College of the Philippines, collapsed during the earthquake, which occurred during school hours. A 20-year-old high school student, Robin Garcia, was later credited with rescuing at least eight students and teachers by twice returning under the rubble to retrieve survivors. Garcia was killed by an aftershock hours after the quake while trying to rescue more survivors, and he received several posthumous tributes, including medals of honor from the Boy Scouts of the Philippines and President Corazon Aquino's Grieving Heart Award for his heroic effort that brought the world's attention to the quake due to quick media coverage in the city, since most of the buildings were damaged save for the CCP building which was collapsed totally. In other areas of Nueva Ecija, a school in Guimba collapsed killing three students. Dagupan In Dagupan, about 90 buildings in the city were damaged, and about 20 collapsed. Some structures sustained damage because liquefaction caused buildings to sink as much as . The earthquake caused a decrease in the elevation of the city and several areas were flooded. The city suffered 64 casualties of which 47 survived and 17 died. Most injuries were sustained during stampedes at a university building and a theater. La Union Five municipalities in La Union were affected: Agoo, Aringay, Caba, Santo Tomas, and Tubao with a combined population of 132,208. Many buildings, including the Agoo Municipal hall, the Museo de Iloko, the parish church of Aringay, collapsed or were severely damaged. 100,000 families were displaced when two coastal villages sank due to liquefaction. The province suffered many casualties leaving 32 people dead. ==Patterns of damage==
Patterns of damage
. Based on preliminary analysis, cases and controls were similar in age and sex distribution. Similar proportions of cases and controls were inside buildings (74% and 80%, respectively) and outside buildings (26% and 20%, respectively) during the earthquake. For persons who were inside a building, risk factors included building height, type of building material, and the floor level the person was on. Persons inside buildings with seven or more floors were 35 times more likely to be injured. Persons inside buildings constructed of concrete or mixed materials were three times more likely to sustain injuries than were those inside wooden buildings. Persons at middle levels of multistory buildings were twice as likely to be injured as those at the top or bottom levels. On July 19, three days after the earthquake, the priority of relief efforts shifted from treatment of injuries to public health concerns. For example, numerous broken pipes completely disrupted water systems, limiting the availability of potable water, and refugees who camped in open areas had no adequate toilet facilities. Early efforts at providing potable water by giving refugees chlorine granules were unsuccessful. Most potable water was distributed from fire engines, and Department of Health (DOH) sanitarians chlorinated the water before it was distributed. Surveys of refugee areas showed few latrines; these had to be dug by the DOH. ==Aftermath==
Aftermath
The University of Baguio, which got struck by this earthquake, was rehabilitated, while the land where Hyatt Terraces stood remains abandoned. ==In popular culture==
In popular culture
The earthquake is featured in the television documentary series by GRB Entertainment, aired on The Learning Channel and other television channels around the world, about natural disasters titled ''Earth's Fury (also known internationally as Anatomy of Disaster) in an episode entitled "Earthquake!", the 50th anniversary special of GMA News and Public Affairs titled Limang Dekada in 2010, the 50th anniversary special of ABS-CBN titled Sa Mata ng Balita in 2003, and the 1996 documentary produced by Langley Productions titled The Amazing Video Collection: Natural Disasters''. Scenes of the earthquake's destruction around Baguio, as well as reflections on Filipino people's capacity to endure and rebuild, also featured in a segment of 1994 collage film directed by National Artist Kidlat Tahimik titled Why is Yellow the Middle of the Rainbow?. ==See also==
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