April 2011 Fukushima earthquake
Encyclopedia
The was a potent magnitude 6.6 Mw
intraplate
aftershock
that occurred at 17:16 JST
(08:16 UTC
) on Monday, 11 April 2011. With a shallow focal depth
of 10 km (6 mi), it was centered inland about 36 km (22 mi) west of Iwaki, Japan
, resulting in widespread moderate to localized strong shaking. The quake was one of many aftershocks to follow the 11 March Tōhoku earthquake, and the strongest to have its epicentre located inland.
The earthquake occurred as a result of normal faulting to the west of Iwaki, and triggered numerous landslides across adjacent mountainous areas. Few fires reportedly broke out, and some 220,000 households suffered power outages. Although localized tsunami alerts were issued, no significant waves were reported. There were no immediate reports of major structural damage, but the quake killed three and injured 10 others.
6.6 (Mw) earthquake occurred inland on 11 April 2011 at 08:16 UTC at a depth of 10 km (6 mi), about 36 km (22 mi) west of Iwaki, Fukushima
, or 161 km (100 mi) north-northeast of Tokyo
. To the east, the oceanic Pacific Plate
is being subducted
beneath the continental Okhotsk Plate
, leading to the formation of inland fault lines near the resultant tectonic boundary
. The quake resulted from normal faulting with some strike-slip component in the Hamadōri region
along the active Idosawa Fault
, which runs a length of nearly 20 km (12 mi). Surveys held near the fault revealed a surface rupture of approximately 6.4 km (4 mi), with a vertical displacement
of between 0.8 to 1.5 m (2.6 to 4.9 ft) and right-lateral slip of about 30 cm (12 in) reported at the lowering west side. Early estimates placed the intensity of the tremor at a magnitude of 7.1, but this was later revised to magnitude 6.6 (Mw) by the USGS. In addition, the Japan Meteorological Agency
placed its intensity at a preliminary magnitude of 7.0.
Although it was centered near a different fault zone, the earthquake was reported to be an aftershock of the 11 March Tōhoku earthquake
, which occurred offshore about 235 km (145 mi) to its northeast. The magnitude 9.0 earthquake triggered widespread seismic activity, and its aftershock sequence includes well-over 58 earthquakes of magnitude 6.0 or greater. Of the aftershocks, three registered higher than magnitude 7.0, with only one of them
directly affecting land. The Fukushima Hamadōri earthquake, however, was the strongest registered aftershock to have its epicentre located inland.
Due to the very shallow focal depth of the quake, heavy shaking was reported in many adjacent areas; the strongest ground motion was registered in Ishikawa town
at VIII (severe) on the Mercalli intensity scale
. Strong shaking (MM VI) was also reported in Iwaki, Sukawaga
, Kuroiso
, Ōtawara
, and Kitaibaraki
, with light tremors (MM IV) felt in areas up to several hundred kilometres from the epicentre, including Tokyo and Yokohama
.
The quake was succeeded by a number of smaller tremors; that same day, at least 11 earthquakes of over magnitude 3.5 were reported near its epicenter. Of the series, the strongest registered at a magnitude of 5.5 (Mw), and occurred within 3.5 hours after the initial quake.
. About 220,000 households reportedly lost power, with most outages occurring in Iwaki city. Workers at the Fukushima Daiichi power plant
— distanced near 70 km (40 mi) from the epicentre — evacuated to safety, while external power to the plant was cut off. The outage briefly disrupted cooling water injections into three of its reactors, though power service was restored by 18:05 local time. Authorities at Tokyo International Airport were forced to close all runway
s momentarily, while voice calls in 14 prefectures were restricted by NTT DoCoMo
following the quake. East Japan Railway Company
temporarily suspended its services to restart four of five bullet-train lines; Shinkansen
bullet trains in the region were also halted. The Jōban Expressway
, which runs from Misato, Saitama
to Tomiya, Miyagi
, was closed from traffic following a mudslide.
The tremor sparked several fires in Iwaki
, with one fire reportedly breaking out in Asakawa town
. Fire trucks extinguished a lightning-induced fire in a liquefied
natural gas tank at Daiichi Sankyo's Onahama Plant. Landslides triggered by the quake crushed two vehicles and buried three homes in Iwaki, trapping a number of inhabitants. Initially, four people were estimated to be trapped, but officials later reported more victims. The incident resulted in at least two immediate deaths; four people were critically injured and hospitalized. One of the injured was later pronounced dead. An additional seven minor injuries were reported in surrounding locations, including southern Ibaraki
, Tochigi
, and Kanagawa
.
postponed a press conference scheduled for 17:50 local time to mark the one-month anniversary of the 11 March Tōhoku earthquake and tsunami, which left extreme devastation in its wake. At the threat of a tsunami
— which reach dangerous wave heights near shallow coastal waters — local fishing boats along coastlines were shown heading out to sea on national news broadcasts. A warning for a localized tsunami of up to 2.0 m (6.6 ft) was issued by the Japan Meteorological Agency
; however, no waves were reported, and the warning was later canceled. The earthquake occurred in a historically inactive seismic region; studies indicated recent activity near the fault zone was triggered by the Tōhoku quake. According to Professor Yagi Hiroshi from the Faculty of Education, Art and Science, "a possibility exists for widespread aftershocks of the same size to occur in the near future."
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
intraplate
Intraplate earthquake
An intraplate earthquake is an earthquake that occurs in the interior of a tectonic plate, whereas an interplate earthquake is one that occurs at a plate boundary....
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...
that occurred at 17:16 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...
(08:16 UTC
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
) on Monday, 11 April 2011. With a shallow focal depth
Hypocenter
The hypocenter refers to the site of an earthquake or a nuclear explosion...
of 10 km (6 mi), it was centered inland about 36 km (22 mi) west of Iwaki, Japan
Iwaki, Fukushima
is a city located in the southern part of the Hamadōri coastal region of Fukushima Prefecture, Japan.A designated "core city", Iwaki is also one of the growing number of hiragana cities. Its area is 1,231.35 km², making it the 10th largest city in Japan...
, resulting in widespread moderate to localized strong shaking. The quake was one of many aftershocks to follow the 11 March Tōhoku earthquake, and the strongest to have its epicentre located inland.
The earthquake occurred as a result of normal faulting to the west of Iwaki, and triggered numerous landslides across adjacent mountainous areas. Few fires reportedly broke out, and some 220,000 households suffered power outages. Although localized tsunami alerts were issued, no significant waves were reported. There were no immediate reports of major structural damage, but the quake killed three and injured 10 others.
Geology
The magnitudeMoment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
6.6 (Mw) earthquake occurred inland on 11 April 2011 at 08:16 UTC at a depth of 10 km (6 mi), about 36 km (22 mi) west of Iwaki, Fukushima
Fukushima Prefecture
is a prefecture of Japan located in the Tōhoku region on the island of Honshu. The capital is the city of Fukushima.-History:Until the Meiji Restoration, the area of Fukushima prefecture was known as Mutsu Province....
, or 161 km (100 mi) north-northeast of Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
. To the east, the oceanic Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
is being subducted
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
beneath the continental Okhotsk Plate
Okhotsk Plate
The Okhotsk Plate is a tectonic plate covering the Sea of Okhotsk, the Kamchatka Peninsula, Sakhalin Island and Tōhoku and Hokkaidō in Japan. It was formerly considered a part of the North American Plate, but recent studies indicate that it is an independent plate, bounded on the north by the...
, leading to the formation of inland fault lines near the resultant tectonic boundary
Convergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
. The quake resulted from normal faulting with some strike-slip component in the Hamadōri region
Hamadori
is an area comprising the easternmost third of Fukushima Prefecture in Japan.The principal city of the area is Iwaki.-History:From the Heian period to the Tensho period, Hamadori was divided by the Iwaki clan and the Soma clan . After the Battle of Sekigahara, the Iwaki clan was banished to...
along the active Idosawa Fault
Idosawa Fault
The is an active earthquake fault with a length of 8 mi , located in Fukushima Prefecture of Japan, to the west of Iwaki city. It mainly consists of a trace of three striations. Although the Idosawa Fault primarily behaves as a normal dip-slip fault, it also consists of a north-trending...
, which runs a length of nearly 20 km (12 mi). Surveys held near the fault revealed a surface rupture of approximately 6.4 km (4 mi), with a vertical displacement
Vertical displacement
In tectonics, vertical displacement is the shifting of land in a vertical direction, resulting in a permanent change in elevation.Two types of vertical displacement are uplift, an increase in elevation, and subsidence, a decrease in elevation....
of between 0.8 to 1.5 m (2.6 to 4.9 ft) and right-lateral slip of about 30 cm (12 in) reported at the lowering west side. Early estimates placed the intensity of the tremor at a magnitude of 7.1, but this was later revised to magnitude 6.6 (Mw) by the USGS. In addition, 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...
placed its intensity at a preliminary magnitude of 7.0.
Although it was centered near a different fault zone, the earthquake was reported to be an aftershock of the 11 March Tōhoku earthquake
2011 Tōhoku earthquake and tsunami
The 2011 earthquake off the Pacific coast of Tohoku, also known as the 2011 Tohoku earthquake, or the Great East Japan Earthquake, was a magnitude 9.0 undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST on Friday, 11 March 2011, with the epicenter approximately east...
, which occurred offshore about 235 km (145 mi) to its northeast. The magnitude 9.0 earthquake triggered widespread seismic activity, and its aftershock sequence includes well-over 58 earthquakes of magnitude 6.0 or greater. Of the aftershocks, three registered higher than magnitude 7.0, with only one of them
April 2011 Miyagi earthquake
The April 2011 Miyagi earthquake was a magnitude 7.1 Mw earthquake, with an epicentre off the coast of Miyagi Prefecture, approximately east of Sendai, Japan...
directly affecting land. The Fukushima Hamadōri earthquake, however, was the strongest registered aftershock to have its epicentre located inland.
Due to the very shallow focal depth of the quake, heavy shaking was reported in many adjacent areas; the strongest ground motion was registered in Ishikawa town
Ishikawa, Fukushima
is a small market town located in Ishikawa District, Fukushima, Japan.During World War II, the town had a secret uranium mine for the Japanese atomic bomb project....
at VIII (severe) on the Mercalli intensity scale
Mercalli intensity scale
The Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude M_w usually reported for an earthquake , which is a measure of the energy released...
. Strong shaking (MM VI) was also reported in Iwaki, Sukawaga
Sukagawa, Fukushima
is a city located in the center of Fukushima, Japan. It is famous for both its peony garden , a national scenic beauty, and its torch festival which has been hereditary for over 400 years....
, Kuroiso
Kuroiso, Tochigi
Kuroiso was a city located in Tochigi, Japan. The city was founded on November 1, 1970.On January 1, 2005 Kurioso was merged with the towns of Nishinasuno and Shiobara, both from Nasu District, to form the new city of Nasushiobara. In 2003, the city had an estimated population of 60,145 and the...
, Ōtawara
Otawara, Tochigi
is a city located in eastern Tochigi Prefecture, Japan which is in the northern part of the Kantō region north of Tokyo. Otawara is approximately 40 kilometers north of Utsunomiya, the capital of Tochigi, and approximately 50 km east of the historic city of Nikkō...
, and Kitaibaraki
Kitaibaraki, Ibaraki
is a city located on the Pacific Ocean in Ibaraki, Japan, between the cities of Hitachi and Iwaki.As of May 1, 2011, the city has an estimated population of 46,465, with a household number of 17,438 and the density of 249.08 persons per km²...
, with light tremors (MM IV) felt in areas up to several hundred kilometres from the epicentre, including Tokyo and Yokohama
Yokohama
is the capital city of Kanagawa Prefecture and the second largest city in Japan by population after Tokyo and most populous municipality of Japan. It lies on Tokyo Bay, south of Tokyo, in the Kantō region of the main island of Honshu...
.
The quake was succeeded by a number of smaller tremors; that same day, at least 11 earthquakes of over magnitude 3.5 were reported near its epicenter. Of the series, the strongest registered at a magnitude of 5.5 (Mw), and occurred within 3.5 hours after the initial quake.
Impact
The earthquake struck during the morning near a moderately populated region; however, most structures around the epicentre were reported to be resistant to earthquake shakingEarthquake engineering
Earthquake engineering is the scientific field concerned with protecting society, the natural and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels...
. About 220,000 households reportedly lost power, with most outages occurring in Iwaki city. Workers at the Fukushima Daiichi power plant
Fukushima I Nuclear Power Plant
The , also known as Fukushima Dai-ichi , is a disabled nuclear power plant located on a site in the towns of Okuma and Futaba in the Futaba District of Fukushima Prefecture, Japan. First commissioned in 1971, the plant consists of six boiling water reactors...
— distanced near 70 km (40 mi) from the epicentre — evacuated to safety, while external power to the plant was cut off. The outage briefly disrupted cooling water injections into three of its reactors, though power service was restored by 18:05 local time. Authorities at Tokyo International Airport were forced to close all runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
s momentarily, while voice calls in 14 prefectures were restricted by NTT DoCoMo
NTT DoCoMo
is the predominant mobile phone operator in Japan. The name is officially an abbreviation of the phrase, "do communications over the mobile network", and is also from a compound word dokomo, meaning "everywhere" in Japanese. Docomo provides phone, video phone , i-mode , and mail services...
following the quake. East Japan Railway Company
East Japan Railway Company
is the largest passenger railway company in the world and one of the seven Japan Railways Group companies. The company name is officially abbreviated as JR East in English, and as in Japanese. The company's headquarters are in Yoyogi, Shibuya, Tokyo....
temporarily suspended its services to restart four of five bullet-train lines; Shinkansen
Shinkansen
The , also known as THE BULLET TRAIN, is a network of high-speed railway lines in Japan operated by four Japan Railways Group companies. Starting with the Tōkaidō Shinkansen in 1964, the network has expanded to currently consist of of lines with maximum speeds of , of Mini-shinkansen with a...
bullet trains in the region were also halted. The Jōban Expressway
Joban Expressway
The , abbreviated , is a national expressway in Japan. It is owned and operated by East Nippon Expressway Company.-Naming:Jōban is a kanji acronym consisting of two characters...
, which runs from Misato, Saitama
Saitama Prefecture
is a prefecture of Japan located in the Kantō region of the island of Honshu. The capital is the city of Saitama.This prefecture is part of the Greater Tokyo Area, and most of Saitama's cities can be described as suburbs of Tokyo, to which a large amount of residents commute each day.- History...
to Tomiya, Miyagi
Tomiya, Miyagi
is a town located in Kurokawa District, Miyagi, Japan.Tomiya was a post station during the feudal age for travelers resting in between the towns of Yoshioka and Sendai.As of 2006, the town has an estimated population of 42,982. The total area is 49.13 km²....
, was closed from traffic following a mudslide.
The tremor sparked several fires in Iwaki
Iwaki, Fukushima
is a city located in the southern part of the Hamadōri coastal region of Fukushima Prefecture, Japan.A designated "core city", Iwaki is also one of the growing number of hiragana cities. Its area is 1,231.35 km², making it the 10th largest city in Japan...
, with one fire reportedly breaking out in Asakawa town
Asakawa, Fukushima
is a town located in Ishikawa District, Fukushima, Japan.As of 2003, the town has an estimated population of 7,280 and a density of 194.50 persons per km². The total area is 37.43 km².-External links:*...
. Fire trucks extinguished a lightning-induced fire in a liquefied
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
natural gas tank at Daiichi Sankyo's Onahama Plant. Landslides triggered by the quake crushed two vehicles and buried three homes in Iwaki, trapping a number of inhabitants. Initially, four people were estimated to be trapped, but officials later reported more victims. The incident resulted in at least two immediate deaths; four people were critically injured and hospitalized. One of the injured was later pronounced dead. An additional seven minor injuries were reported in surrounding locations, including southern Ibaraki
Ibaraki Prefecture
is a prefecture of Japan, located in the Kantō region on the main island of Honshu. The capital is Mito.-History:Ibaraki Prefecture was previously known as Hitachi Province...
, Tochigi
Tochigi Prefecture
is a prefecture located in the Kantō region on the island of Honshū, Japan. The capital is the city of Utsunomiya.Nikkō, whose ancient Shintō shrines and Buddhist temples UNESCO has recognized by naming them a World Heritage Site, is in this prefecture...
, and Kanagawa
Kanagawa Prefecture
is a prefecture located in the southern Kantō region of Japan. The capital is Yokohama. Kanagawa is part of the Greater Tokyo Area.-History:The prefecture has some archaeological sites going back to the Jōmon period...
.
Response
In response to the tremor, Prime Minister Naoto KanNaoto Kan
is a Japanese politician, and former Prime Minister of Japan. In June 2010, then-Finance Minister Kan was elected as the leader of the Democratic Party of Japan and designated Prime Minister by the Diet to succeed Yukio Hatoyama. On 26 August 2011, Kan announced his resignation...
postponed a press conference scheduled for 17:50 local time to mark the one-month anniversary of the 11 March Tōhoku earthquake and tsunami, which left extreme devastation in its wake. At the threat of a tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
— which reach dangerous wave heights near shallow coastal waters — local fishing boats along coastlines were shown heading out to sea on national news broadcasts. A warning for a localized tsunami of up to 2.0 m (6.6 ft) was issued by 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...
; however, no waves were reported, and the warning was later canceled. The earthquake occurred in a historically inactive seismic region; studies indicated recent activity near the fault zone was triggered by the Tōhoku quake. According to Professor Yagi Hiroshi from the Faculty of Education, Art and Science, "a possibility exists for widespread aftershocks of the same size to occur in the near future."
See also
- List of foreshocks and aftershocks of the 2011 Tōhoku earthquake
- April 2011 Miyagi earthquakeApril 2011 Miyagi earthquakeThe April 2011 Miyagi earthquake was a magnitude 7.1 Mw earthquake, with an epicentre off the coast of Miyagi Prefecture, approximately east of Sendai, Japan...
- List of earthquakes in Japan
External links
- CBS News Video - Japan hit with 6.6 aftershock
- Earthquake Report from United States Geological SurveyUnited States Geological SurveyThe United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
(USGS)