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 Home>>The 2011 Tōhoku earthquake and tsunami.

The 2011 TōHoku Earthquake And Tsunami.

The 2011 Tōhoku earthquake and tsunami (東北地方太平洋沖地震 Tōhoku Chihō Taiheiyō-oki Jishin[6]?, literally "Tōhoku region Pacific Ocean offshore earthquake"[fn 1]) was a 9.0-magnitude megathrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC) on Friday 11 March 2011.[2][3][7] The epicenter was 130 kilometers (81 mi) off the east coast of the Oshika Peninsula of Tōhoku near Sendai, with the hypocenter at a depth of 32 km (19.9 mi).[8][9]

The earthquake triggered extremely destructive tsunami waves of up to 10 meters (33 ft) that struck Japan minutes after the quake, in some cases traveling up to 10 km (6 mi) inland,[10] with smaller waves reaching many other countries after several hours. Tsunami warnings were issued and evacuations ordered along Japan's Pacific coast and at least 20 other countries, including the entire Pacific coast of North America and South America.[11][12][13]

The Japanese National Police Agency has officially confirmed 8,649 deaths,[4][5] 2,702 injured,[4][5] and 12,877 people missing[4][5] across eighteen prefectures, as well as over 125,000 buildings damaged or destroyed.[4][5] The earthquake and tsunami caused extensive and severe structural damage in Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse.[10][14] Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water.[15] Many electrical generators were taken down, and at least three nuclear reactors suffered explosions due to hydrogen gas that had built up within their outer containment buildings. On 18 March, International Atomic Energy Agency Chief Yukiya Amano described the crisis as "extremely serious."[16] Residents within a 20 km (12 mi) radius of the Fukushima I Nuclear Power Plant and a 10 km (6 mi) radius of the Fukushima II Nuclear Power Plant were evacuated.

Estimates of the Tōhoku earthquake's magnitude make it the most powerful known earthquake to hit Japan, and one of the five most powerful earthquakes in the world overall since modern record-keeping began in 1900.[7][17][18] Japanese Prime Minister Naoto Kan said that "in the 65 years after the end of World War II, this is the toughest and the most difficult crisis for Japan."[19] The earthquake moved Honshu 2.4 m (7.9 ft) east and shifted the Earth on its axis by almost 10 cm (3.9 in).[20][21] Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion.[22] The Bank of Japan offered ¥15 trillion (US$183 billion) to the banking system on 14 March in an effort to normalize market conditions.

Earthquake

Map of the Tōhoku earthquake and aftershocks

The 9.0-magnitude (MW) megathrust earthquake occurred on 11 March 2011 at 14:46 JST in the western Pacific Ocean, 130 kilometers (81 mi) east of Sendai, Honshu, Japan, lasting approximately six minutes.[1] Its epicenter was 373 km (232 mi) from Tokyo, according to the United States Geological Survey (USGS) and Japanese Meteorological Agency (JMA). The main earthquake was preceded by a number of large foreshocks, and multiple aftershocks were reported afterwards. The first major foreshock was a 7.2 MW event on 9 March, approximately 40 km (25 mi) from the 11 March quake, with another three on the same day in excess of 6.0 MW.[2][24] Following the quake, a 7.0 MW aftershock was reported at 15:06 JST, followed by a 7.4 at 15:15 JST and a 7.2 at 15:26 JST.[25] Over six hundred aftershocks of magnitude 4.5 or greater have occurred since the initial quake.[26] USGS director Marcia McNutt explained that aftershocks follow Omori's Law, might continue for years, and will taper off in time.[27]

One minute prior to the effects of the earthquake being felt in Tokyo, the Earthquake Early Warning system, which includes more than 1,000 seismometers in Japan, sent out warnings of an impending earthquake to millions. This was possible because the damaging seismic S-waves, traveling at 4 km (2.5 mi) per second, took about 90 seconds to travel the 373 km (232 mi) to Tokyo. The early warning is believed by the JMA to have saved many lives.[28][29]

Soil liquefaction in Koto, Tokyo

Initially reported as 7.9 MW by the USGS, the magnitude was quickly upgraded to 8.8 and then to 8.9,[30] and then again to 9.0.[31][3] This earthquake occurred where the Pacific Plate is subducting under the plate beneath northern Honshu; which plate this is is a matter of debate amongst scientists.[32][21] The Pacific plate, which moves at a rate of 8 to 9 cm (3.1 to 3.5 in) a year, dips under Honshu's underlying plate releasing large amounts of energy. This motion pulls the upper plate down until the stress builds up enough to cause a seismic event. The break 130 kilometers (81 mi) off of the coast of Sendai was estimated to be several tens of kilometers long and only 32 km (19.9 mi) deep, and caused the sea floor to spring up several meters, causing the earthquake.[32][33] A quake of this size usually has a rupture length of at least 480 km (300 mi) and requires a long, relatively straight fault line. Because the plate boundary and subduction zone in this region is not very straight, it is unusual for the magnitude of an earthquake to exceed 8.5; the magnitude of this earthquake was a surprise to some seismologists.[34] The hypocentral region of this earthquake extends from offshore Iwate Prefecture to offshore Ibaraki Prefecture.[35] The Japanese Meteorological Agency said that the earthquake may have ruptured the fault zone from Iwate to Ibaraki with a length of 500 km (310 mi) and a width of 200 km (120 mi).[36][37] Analysis showed that this earthquake consisted of a set of three events.[38] The earthquake may have had a mechanism similar to that of another large earthquake in 869 with an estimated surface wave magnitude (Ms) of 8.6, which also created a large tsunami.[39] Other major earthquakes with tsunamis struck the Sanriku Coast region in 1896 and in 1933.

The quake registered at the maximum of 7 on the Japan Meteorological Agency seismic intensity scale in Kurihara, Miyagi Prefecture.[40] Three other prefectures—Fukushima, Ibaraki and Tochigi—recorded an upper 6 on the JMA scale. Seismic stations in Iwate, Gunma, Saitama and Chiba Prefecture measured a lower 6, recording an upper 5 in Tokyo.

Japan's National Research Institute for Earth Science and Disaster Prevention (NIED) recorded a maximum vector sum(3 component) peak ground acceleration of 2.99g (29.33 m/s²).[41][fn 2]

Energy

This earthquake released a surface energy (Me) of 1.9±0.5×1017 joules,[44] dissipated as shaking and tsunamic energy, which is nearly double that of the 9.1-magnitude 2004 Indian Ocean earthquake and tsunami that killed 230,000 people, and flung the 2,600 ton Apung 1 ship 2 to 3 km (1.2 to 1.9 mi) inland. "If we could only harness the [surface] energy from this earthquake, it would power [a] city the size of Los Angeles for an entire year," McNutt said in an interview.[27] The total energy released, also known as the seismic moment (M0), was more than 200,000 times the surface energy and was calculated by the USGS at 3.9×1022 joules,[45] slightly less than the 2004 Indian Ocean quake. This is equivalent to 9.32 teratons of TNT, or approximately 600 million times the energy of the Hiroshima bomb.

Geophysical impact

The quake moved portions of northeast Japan by as much as 2.4 meters (7.9 ft) closer to North America,[20][21] making portions of Japan's landmass "wider than before," according to geophysicist Ross Stein.[21] Portions of Japan closest to the epicenter experienced the largest shifts.[21] Stein also noted that a 400-kilometer (250 mi) stretch of coastline dropped vertically by 0.6 m (2.0 ft), allowing the tsunami to travel farther and faster onto land.[21] The Pacific plate itself may have moved westwards by up to 20 m (66 ft), though the actual displacement will have diminished with greater distance from the site of the fault.[46] Other estimates put the amount of slippage at as much as 40 m (130 ft), covering an area some 300 to 400 km (190 to 250 mi) long by 100 km (62 mi) wide. If confirmed, this would be one of the largest recorded fault movements to have been associated with an earthquake.[47]

Street and manhole damage after the earthquake

According to Italy's National Institute of Geophysics and Volcanology, the earthquake shifted the Earth's axis by 25 centimeters (9.8 in). This deviation led to a number of small planetary changes, including the length of a day and the tilt of the Earth.[48] The speed of the Earth's rotation increased, shortening the day by 1.8 microseconds due to the redistribution of Earth's mass.[49] The axial shift was caused by the redistribution of mass on the Earth's surface, which changed the planet's moment of inertia. Due to the effects of conservation of angular momentum, such changes of inertia result in small changes to the Earth's rate of rotation.[50] These are expected changes[48] for an earthquake of this magnitude.[20][49]

Shinmoedake, a volcano in Kyushu, erupted two days after the earthquake. The volcano had erupted in January 2011; it is not known if the later eruption was linked to the earthquake.[51] In Antarctica, the seismic waves from the earthquake were reported to have caused the Whillans Ice Stream to slip by about 0.5 m (1.6 ft). 

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