2005 Fukuoka earthquake
Encyclopedia
The Fukuoka earthquake struck Fukuoka Prefecture
, Japan at 10:53 am JST
on March 20, 2005, and lasted for approximately 1 minute. The Japan Meteorological Agency
(JMA) measured it as peaking at a magnitude of 7.0 (6.6) and named it and its subsequent aftershocks the . The quake occurred along a previously unknown fault in the Genkai Sea, North of Fukuoka
city, and the residents of Genkai island were forced to evacuate as houses collapsed and landslides occurred in places. Investigations subsequent to the earthquake determined that the new fault was most likely an extension of the known Kego fault that runs through the centre of the city.
Fukuoka is not as seismically active as many other parts of Japan, and was known prior to the earthquake as one of Japan's safest locations in terms of natural disasters; the previous earthquake, a magnitude 5, had occurred over a hundred years ago and it had been centuries since the city had experienced a serious earthquake.
The earthquake occurred along a yet-undiscovered extension of the Kego fault in the Sea of Genkai, with Genkai-jima (Genkai island), a part of Nishi-ku
, being most severely damaged by this earthquake and almost all island residents being forced to evacuate. One person was killed, 70 people were severely injured and 1017 received attention for minor injuries. Aftershock
s continued intermittently throughout the following weeks as construction crews worked to rebuild damaged buildings throughout the city. Traditional Japanese houses, particularly in the areas of Daimyō
and Imaizumi, were the most heavily damaged and many were marked for demolition. Insurance payments for damages were estimated at approximately 15.8 billion yen.
Fukuoka's most famous major fault, the Kego fault, runs northwest to southeast, roughly parallel to Nishitetsu
's Ōmuta train line
, and was thought to be 22 km long, terminating at Hakata Bay. It is estimated to be able to produce earthquakes as strong as magnitude 7 at the epicenter approximately once every 15,000 years. When a center is located at a depth of 10 km, it would cause an earthquake of a lower-6 magnitude (similar to the March 20, 2005 earthquake) in downtown Fukuoka. The probability
of an earthquake along the known length of the Kego fault occurring within 30 years was estimated at 0.4% prior to the March 20, 2005 earthquake, but this probability has been revised upwards since. According to a National Institute of Advanced Industrial Science and Technology presentation April 12, 2005http://www.asahi.com/special/050320/TKY200504120267.html, supposing the last Kego earthquake had occurred 13,000 years ago, the probability of major activity within 30 years had been revised to 7%, or it were 7,000 years ago, the probability had been revised to 4%. Suppose that an earthquake had occurred along the Kego fault within the last 2000 years, the risk would be unchanged.
In order to more accurately estimate the risk of ongoing or increased seismic activity, teams from Tokyo University
, Kōchi University
, Hiroshima University
and Ōita University
surveyed Hakata Bay to determine how far the Kego fault extends. Preliminary results, announced May 1, 2005 indicated that the fault extends nearly as far as Nokonoshima, 2.5 km out in to the bay, though no sign of recent activity along the fault was uncovered. The teams also discovered a new fault in the Higashi-ku portion of Hakata Bay. Later findings indicated that the faultline responsible for both the March 20 and April 20 quakes was likely an extension of the Kego fault, making its total length approximately 40 km.
Fukuoka Prefecture
is a prefecture of Japan located on Kyūshū Island. The capital is the city of Fukuoka.- History :Fukuoka Prefecture includes the former provinces of Chikugo, Chikuzen, and Buzen....
, Japan at 10:53 am JST
Japan Standard Time
Japan Standard Time or JST is the standard timezone of Japan, and is 9 hours ahead of UTC. For example, when it is midnight in UTC, it is 09:00 in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times. Japan Standard Time is the same as...
on March 20, 2005, and lasted for approximately 1 minute. The Japan Meteorological Agency
Japan Meteorological Agency
The or JMA, is the Japanese government's weather service. Charged with gathering and reporting weather data and forecasts in Japan, it is a semi-autonomous part of the Ministry of Land, Infrastructure and Transport...
(JMA) measured it as peaking at a magnitude of 7.0 (6.6) and named it and its subsequent aftershocks the . The quake occurred along a previously unknown fault in the Genkai Sea, North of Fukuoka
Fukuoka, Fukuoka
is the capital city of Fukuoka Prefecture and is situated on the northern shore of the island of Kyushu in Japan.Voted number 14 in a 2010 poll of the World's Most Livable Cities, Fukuoka is praised for its green spaces in a metropolitan setting. It is the most populous city in Kyushu, followed by...
city, and the residents of Genkai island were forced to evacuate as houses collapsed and landslides occurred in places. Investigations subsequent to the earthquake determined that the new fault was most likely an extension of the known Kego fault that runs through the centre of the city.
Fukuoka is not as seismically active as many other parts of Japan, and was known prior to the earthquake as one of Japan's safest locations in terms of natural disasters; the previous earthquake, a magnitude 5, had occurred over a hundred years ago and it had been centuries since the city had experienced a serious earthquake.
The earthquake occurred along a yet-undiscovered extension of the Kego fault in the Sea of Genkai, with Genkai-jima (Genkai island), a part of Nishi-ku
Nishi-ku, Fukuoka
is one of the seven wards of Fukuoka City, Japan. Meaning literally "west ward," it is bordered to the east by Sawara-ku, and to the west by Maebaru and Shima. As of 2003, it has a population of 173,813 people and an area of 83.81 km2...
, being most severely damaged by this earthquake and almost all island residents being forced to evacuate. One person was killed, 70 people were severely injured and 1017 received attention for minor injuries. Aftershock
Aftershock
An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock...
s continued intermittently throughout the following weeks as construction crews worked to rebuild damaged buildings throughout the city. Traditional Japanese houses, particularly in the areas of Daimyō
Daimyo
is a generic term referring to the powerful territorial lords in pre-modern Japan who ruled most of the country from their vast, hereditary land holdings...
and Imaizumi, were the most heavily damaged and many were marked for demolition. Insurance payments for damages were estimated at approximately 15.8 billion yen.
Fukuoka's most famous major fault, the Kego fault, runs northwest to southeast, roughly parallel to Nishitetsu
Nishi-Nippon Railroad
The , also called or NNR, is one of Japan's "Big 16" private railroad companies. With headquarters in Fukuoka, it operates local and highway buses, supermarkets, real-estate and travel agencies, as well as railways in Fukuoka Prefecture. In addition, from 1950 to 1972, the company owned the Lions...
's Ōmuta train line
Tenjin Omuta Line
The is a heavy rail line in Fukuoka Prefecture in Kyūshū, Japan, being the main line of a Japanese private railway company Nishi-Nippon Railroad . The line is from Nishitetsu Fukuoka Station in Chūō-ku, Fukuoka, stretching south to Ōmuta Station in Ōmuta...
, and was thought to be 22 km long, terminating at Hakata Bay. It is estimated to be able to produce earthquakes as strong as magnitude 7 at the epicenter approximately once every 15,000 years. When a center is located at a depth of 10 km, it would cause an earthquake of a lower-6 magnitude (similar to the March 20, 2005 earthquake) in downtown Fukuoka. The probability
Probability
Probability is ordinarily used to describe an attitude of mind towards some proposition of whose truth we arenot certain. The proposition of interest is usually of the form "Will a specific event occur?" The attitude of mind is of the form "How certain are we that the event will occur?" The...
of an earthquake along the known length of the Kego fault occurring within 30 years was estimated at 0.4% prior to the March 20, 2005 earthquake, but this probability has been revised upwards since. According to a National Institute of Advanced Industrial Science and Technology presentation April 12, 2005http://www.asahi.com/special/050320/TKY200504120267.html, supposing the last Kego earthquake had occurred 13,000 years ago, the probability of major activity within 30 years had been revised to 7%, or it were 7,000 years ago, the probability had been revised to 4%. Suppose that an earthquake had occurred along the Kego fault within the last 2000 years, the risk would be unchanged.
M5.8 aftershock on April 20
A new after-quake hit at 6:11 a.m. April 20 on Japan's southern main island of Kyūshū, the Central Meteorological Agency reported. Although considerable time had passed since the first quake, the aftershock was not unexpected. The quake, which swayed buildings and shattered some outer walls, was measured to have magnitude of 5.8. 2 and 56 people were severely and slightly injured and treated at a hospital in Fukuoka due to the quake and there were temporary closures of major highways, railway services and Fukuoka's airport. Following reports that the city has only prepared for earthquakes up to a magnitude of 6.5, the aftershock renewed fears that the quakeshttp://www.sevo.kyushu-u.ac.jp/HYPO/ might cause the Kego faultline to become active again beneath Fukuoka, leading to an earthquake as big as, or bigger than, the March 20 quake.In order to more accurately estimate the risk of ongoing or increased seismic activity, teams from Tokyo University
University of Tokyo
, abbreviated as , is a major research university located in Tokyo, Japan. The University has 10 faculties with a total of around 30,000 students, 2,100 of whom are foreign. Its five campuses are in Hongō, Komaba, Kashiwa, Shirokane and Nakano. It is considered to be the most prestigious university...
, Kōchi University
Kochi University
is a national university in Kōchi, Kōchi, Japan. The predecessor of the school was founded in 1922, and it was chartered as a university in 1949.-External links:*...
, Hiroshima University
Hiroshima University
, located in the Japanese cities of Higashihiroshima and Hiroshima, was established 1949 by the merger of a number of national educational institutions.-History:Under the National School Establishment Law, Hiroshima University was established on May 31, 1949...
and Ōita University
Oita University
is a national university in Ōita, Ōita, Japan. The precursor of the school was founded in 1921 and was chartered as a university in 1949....
surveyed Hakata Bay to determine how far the Kego fault extends. Preliminary results, announced May 1, 2005 indicated that the fault extends nearly as far as Nokonoshima, 2.5 km out in to the bay, though no sign of recent activity along the fault was uncovered. The teams also discovered a new fault in the Higashi-ku portion of Hakata Bay. Later findings indicated that the faultline responsible for both the March 20 and April 20 quakes was likely an extension of the Kego fault, making its total length approximately 40 km.