A potent
magnitude 6.6 Mw intraplate aftershock
In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...
occurred at 17:16
JST (08:16
UTC) on 11 April, in the
Hamadōri
is the easternmost of the three regions of Fukushima Prefecture, Japan, the other two being Nakadōri in the central area of the prefecture and Aizu in the west. Hamadōri is bordered by the Abukuma Highlands to the west and the Pacific Ocea ...
region of
Fukushima
may refer to:
Japan
* Fukushima Prefecture, Japanese prefecture
** Fukushima, Fukushima, capital city of Fukushima Prefecture, Japan
***Fukushima University, national university in Japan
*** Fukushima Station (Fukushima) in Fukushima, Fukushim ...
,
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
. With a shallow
focus
Focus, or its plural form foci may refer to:
Arts
* Focus or Focus Festival, former name of the Adelaide Fringe arts festival in South Australia Film
*''Focus'', a 1962 TV film starring James Whitmore
* ''Focus'' (2001 film), a 2001 film based ...
of , the earthquake was centred inland about west of
Iwaki, causing widespread strong to locally severe shaking. It 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. A few fires broke out, and 220,000 households lost electricity. Officials issued localised
tsunami alerts, though no significant waves were generated. The earthquake caused little structural damage, but killed four people and injured ten others. The strong ground movements triggered the reactivation of a nearby
geological fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
, prompting researchers to conduct extensive
surveys in the region.
Geology
The
magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
6.6 M
w Fukushima Hamadōri earthquake occurred inland on 11 April 2011 at 08:16 UTC at a
focal depth
In seismology, the depth of focus or focal depth refers to the depth at which an earthquake occurs. Earthquakes occurring at a depth of less than are classified as shallow-focus earthquakes, while those with a focal depth between and are commonl ...
of , about west of
Iwaki, Fukushima
is a city located in Fukushima Prefecture, Japan. , Iwaki had a population of 337,765 in 143,500 households, and population density of 270 persons per km2. The total area of the city is , making it the largest city in the prefecture and the 10th ...
, or north-northeast of
Tokyo
Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, with an estimated 37.468 ...
.
To the east of the
epicentre
The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates.
Surface damage
Before the instrumental pe ...
, the oceanic
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate.
The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...
is
subducted
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
beneath the continental
Okhotsk Plate
The Okhotsk Plate is a minor tectonic plate covering the Kamchatka Peninsula, Magadan Oblast, and Sakhalin Island of Russia; Hokkaido, Kantō and Tōhoku regions of Japan; the Sea of Okhotsk, as well as the disputed Kuril Islands. It was ...
, on which much of
Honshu
, historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island separ ...
's
Tōhoku region
The , Northeast region, or consists of the northeastern portion of Honshu, the largest island of Japan. This traditional region consists of six prefectures (''ken''): Akita, Aomori, Fukushima, Iwate, Miyagi, and Yamagata.
Tōhoku retains a ...
is situated. Building
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
near the resultant
plate boundary
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
has led to the development of shallow inland
faults through
crustal deformation
Deformation can refer to:
* Deformation (engineering), changes in an object's shape or form due to the application of a force or forces.
** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies.
* Defor ...
and
folding
Fold, folding or foldable may refer to:
Arts, entertainment, and media
* ''Fold'' (album), the debut release by Australian rock band Epicure
* Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot
*Abov ...
along the east coast of Tōhoku.
This
intraplate earthquake
The term intraplate earthquake refers to a variety of earthquake that occurs ''within the interior'' of a tectonic plate; this stands in contrast to an interplate earthquake, which occurs ''at the boundary'' of a tectonic plate. Intraplate earth ...
occurred in the vicinity of the
Idosawa Fault – a shallow crustal fault in the
Hamadōri region near
Tabito town, Iwaki city, that had previously been inactive.
Surveys near the epicentre revealed a
surface rupture
In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a fault affects the Earth's surface. Surface rupture is opposed by buried rupture, where the ...
of about and numerous
fault scarp
A fault scarp is a small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other. It is the topographic expression of faulting attributed to the displacement of the land surface by movement al ...
s, with general
vertical displacement
In tectonics, vertical displacement refers to the shifting of land in a vertical direction, resulting in uplift and subsidence. The displacement of rock layers can provide information on how and why Earth's lithosphere changes throughout geolog ...
s of ; a maximum displacement of occurred at the small village of Shionohira. Localised
right-lateral slip of was observed at the subsiding west side of the rupture. The segments of the Idosawa Fault associated with this surface feature were classified as the "Shionohira Fault" in 2011.
The nearby
Yunodake Fault, a normal dip-slip fault northeast of the Shionohira Fault that had been dormant for 120,000–130,000 years, also ruptured during the quake.
These observations indicated that the earthquake occurred as a result of
normal dip-slip faulting with some
strike-slip
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
component.
Although it was centred near a different fault zone, the earthquake was classified as an aftershock of the
11 March Tōhoku earthquake, which occurred offshore about to its northeast.
The magnitude 9.0 M
w earthquake triggered widespread seismic activity, and its aftershock sequence includes well-over 67 earthquakes of magnitude 6.0 M
w or greater.
Apart from the Fukushima Hamadōri earthquake, four of the aftershocks measured magnitude 7.0 M
w or higher.
The Fukushima Hamadōri earthquake, however, was the strongest of the aftershocks to have its epicentre located inland.
Early estimates placed the strength of the earthquake at a magnitude of 7.0–7.1, but the
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the 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, ...
(USGS) lowered the magnitude to 6.6.
The
Japan Meteorological Agency
The , abbreviated JMA, is an agency of the Ministry of Land, Infrastructure, Transport and Tourism. It is charged with gathering and providing results for the public in Japan that are obtained from data based on daily scientific observation an ...
(JMA) assessed a magnitude of 7.0 M
j and a depth of .
The Fukushima Hamadōri earthquake was succeeded by a number of smaller tremors; that same day, at least 11 earthquakes of magnitude 3.5 M
j or higher were recorded near its epicentre.
Of the series, the strongest registered at a magnitude of 5.5 M
j and occurred within 3.5 hours after the initial quake. A shallow magnitude 6.0 M
w (6.4 M
j) earthquake and several smaller tremors struck the region on 12 April.
Effects
![April11 2011 Fukushima earthquake shake map](https://upload.wikimedia.org/wikipedia/commons/a/ab/April11_2011_Fukushima_earthquake_shake_map.jpg)
The earthquake struck in the late afternoon near a moderately populated region of the Fukushima Prefecture, although most structures around the epicentre were
resistant to earthquake shaking.
Focussed at an unusually shallow depth, the earthquake generated significant shaking throughout many adjacent prefectures. The strongest
ground motion
Ground motion is the movement of the earth's surface from earthquakes or explosions. Ground motion is produced by seismic waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the earth a ...
registered at severe (MM VIII) in
Ishikawa town on the
Mercalli intensity scale
The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...
.
Strong shaking (MM VI) spread through Iwaki,
Sukawaga,
Kuroiso,
Ōtawara
270px, View from the ruins of Ōtawara Castle
is a city located in Tochigi Prefecture, Japan. , the city had an estimated population of 72,189 in 30,136 households, and a population density of 210 persons per km2. The total area of the city is ...
and
Kitaibaraki, with light tremors (MM IV) felt in areas up to several hundred kilometres from the epicentre, including Tokyo and
Yokohama
is the second-largest city in Japan by population and the most populous municipality of Japan. It is the capital city and the most populous city in Kanagawa Prefecture, with a 2020 population of 3.8 million. It lies on Tokyo Bay, south of To ...
.
The earthquake cut electricity to about 220,000 households, with most of the cuts reported in Iwaki city.
Workers at the
Fukushima Daiichi power plant – distanced from the epicentre
– evacuated to safety, and external power to the plant was cut. The outage briefly disrupted cooling water injections into three of the reactors, but services to the plant were restored by 18:05 JST.
Authorities at
Tokyo International Airport
, officially , and sometimes called as Tokyo Haneda Airport or Haneda International Airport , is one of two international airports serving the Greater Tokyo Area, the other one being Narita International Airport (NRT). It serves as the primary ...
closed all
runway
According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface (often asphalt concrete, as ...
s momentarily, while
NTT DoCoMo restricted voice calls in 14 prefectures following the quake.
East Japan Railway Company
The is a major passenger railway company in Japan and is the largest of the seven Japan Railways Group companies. The company name is officially abbreviated as JR-EAST or JR East in English, and as in Japanese. The company's headquarters are ...
temporarily suspended its services to restart four of five bullet-train lines; other
Shinkansen
The , colloquially known in English as the bullet train, is a network of high-speed railway lines in Japan. Initially, it was built to connect distant Japanese regions with Tokyo, the capital, to aid economic growth and development. Beyond l ...
bullet trains in the region were also halted.
The earthquake sparked several fires in Iwaki, with one fire breaking out in
Asakawa town. Fire engines extinguished a blaze in a
liquefied natural gas tank at
Daiichi Sankyo
is a global pharmaceutical company and the second-largest pharmaceutical company in Japan. It achieved JPY 981.8 billion in revenue in 2019. The company owns the American biotechnology company Plexxikon, American pharmaceutical company American R ...
's Onahama Plant.
Most of the structural damage was due to scattered rock- and landslides along hillsides in the vicinity of Iwaki. A landslide crushed two vehicles and buried three homes in the city, trapping a number of the inhabitants.
The incident resulted in two immediate deaths. Four people were critically injured and taken to hospital; one of them was later pronounced dead.
The Iwaki Ibaraki Route 14
interchange of the
Jōban Expressway
The , abbreviated , is a national expressway in Japan. It is owned and operated by East Nippon Expressway Company. It is signed E6 under the Ministry of Land, Infrastructure, Transport and Tourism's "2016 Proposal for Realization of Expressway N ...
, which runs from
Misato,
Saitama, to
Tomiya, Miyagi
is a city located in central Miyagi Prefecture, Japan. , the city had an estimated population of 52,433, and a population density of 1,100 persons per km² in 19,535 households. The total area of the city is .
Geography
Tomiya is located in cen ...
, was cut off to traffic by a large landslide of .
In
Tabito town, very close to the epicentre, a landslide resulted in the formation of a
quake lake
Quake Lake (officially Earthquake Lake) is a lake in the
western United States, on the Madison River in southwestern Montana. It was created after an earthquake struck on August 17, 1959, with 28 fatalities. Northwest of West Yellowstone, Qu ...
– a natural
dam
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
ming of a river by
mass wasting
Mass wasting, also known as mass movement, is a general term for the movement of rock or soil down slopes under the force of gravity. It differs from other processes of erosion in that the debris transported by mass wasting is not entrained in ...
– with a water level of and a storage volume of 1,000–2,500 m
3 (35,000–90,000 cu ft).
Significant land deformation with traces of
uplift
Uplift may refer to: Science
* Geologic uplift, a geological process
** Tectonic uplift, a geological process
* Stellar uplift, the theoretical prospect of moving a stellar mass
* Uplift mountains
* Llano Uplift
* Nemaha Uplift
Business
* Uplif ...
was observed in and around town, affecting local roads but largely sparing its structures.
A total of seven people from other regions near the epicentre, including southern
Ibaraki,
Tochigi and
Kanagawa
is a Prefectures of Japan, prefecture of Japan located in the Kantō region of Honshu. Kanagawa Prefecture is the List of Japanese prefectures by population, second-most populous prefecture of Japan at 9,221,129 (1 April 2022) and third-dens ...
prefectures, suffered minor injuries.
Another person was injured during the magnitude 6.0 (M
w) aftershock of 12 April.
In a report from July 2011, the Fire and Disaster Management Agency confirmed a death toll of four from the earthquake.
Response
Japan's
Earthquake Early Warning
An earthquake warning system or earthquake early warning system is a system of accelerometers, seismometers, communication, computers, and alarms that is devised for notifying adjoining regions of a substantial earthquake while it is in progress ...
system was activated upon the detection of
primary waves –
seismic waves
A seismic wave is a wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy. ...
that forego an earthquake's perceivable ground motions – giving residents 6.8 seconds to seek cover before the main shock.
At the risk of a
tsunami
A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...
– which reach their destructive 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 localised tsunami of up to was issued by the Japan Meteorological Agency; however, no significant waves were recorded, and the warning was cancelled soon thereafter.
In response to the earthquake, the fire department dispatched search and rescue teams and emergency crews for relief efforts and damage assessments throughout the affected area. Six medical crews in pairs of two were also sent to Kanagawa,
Chiba
Chiba may refer to:
Places China
* (), town in Jianli County, Jingzhou, Hubei
Japan
* Chiba (city), capital of Chiba Prefecture
** Chiba Station, a train station
* Chiba Prefecture, a sub-national jurisdiction in the Greater Tokyo Area on ...
and
Gunma
is a prefecture of Japan located in the Kantō region of Honshu. Gunma Prefecture has a population of 1,937,626 (1 October 2019) and has a geographic area of 6,362 km2 (2,456 sq mi). Gunma Prefecture borders Niigata Prefecture and Fukushima P ...
prefectures.
Former Prime Minister
Naoto Kan
is a Japanese politician who was Prime Minister of Japan and President of the Democratic Party of Japan (DPJ) from June 2010 to September 2011. Kan was the first Prime Minister since the resignation of Junichiro Koizumi in 2006 to serve for m ...
postponed a press conference scheduled for 17:50 JST marking the one-month anniversary of the catastrophic Tōhoku earthquake and tsunami.
The Fukushima Hamadōri earthquake occurred in a region with historically low levels of seismicity; studies showed that the recent activity near the fault zone had been triggered by the Tōhoku earthquake.
Ever since the earthquake triggered their reactivation, the Shionohira and Yunodake faults have provided essential data for local
geological survey
A geological survey is the systematic investigation of the geology beneath a given piece of ground for the purpose of creating a geological map or model. Geological surveying employs techniques from the traditional walk-over survey, studying outc ...
s on regional land deformation,
sedimentary rock
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
distribution and landslide vulnerability.
In the earthquake's aftermath, Professor Yagi Hiroshi from the Faculty of Education, Art and Science noted that "a possibility exists for widespread aftershocks of the same size to occur in the near future."
See also
*
List of earthquakes in 2011
This is a list of earthquakes in 2011. Only earthquakes of magnitude 6 or above are included, unless they result in damage and/or casualties, or are notable for some other reason. All dates are listed according to UTC time. The 9.1 Tōhoku ear ...
*
List of earthquakes in Japan
This is a list of earthquakes in Japan with either a magnitude greater than or equal to 7.0 or which caused significant damage or casualties. As indicated below, magnitude is measured on the Richter magnitude scale (''ML'') or the moment magnitud ...
*
2016 Fukushima earthquake
The 2016 Fukushima earthquake struck Japan east-southeast of Namie, Fukushima Prefecture at 05:59 JST on November 22 (20:59 Nov 21 UTC) with depth of . Fukushima is a very dense prefecture in Japan north of Tokyo, with a population of nearly ...
*
2021 Fukushima earthquake
References
External links
Japan hit with 6.6 aftershock–
CBS News
CBS News is the news division of the American television and radio service CBS. CBS News television programs include the ''CBS Evening News'', ''CBS Mornings'', news magazine programs '' CBS News Sunday Morning'', '' 60 Minutes'', and '' 48 H ...
Earthquake M6.6 - eastern Honshu, Japan–
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the 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, ...
{{good article
Earthquakes of the Heisei period
2011 earthquakes
April 2011 events in Japan
Landslides in Japan
Earthquakes in Fukushima Prefecture
2011 disasters in Japan