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2011 Tōhoku earthquake and tsunami
"2011 Miyagi earthquake" redirects here. For the aftershock that occurred on 7 April, see April 2011 Miyagi earthquake.
 An aerial view of damage in the Sendai region with black smoke coming from the Nippon Oil Sendai oil refinery | |
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| Date | Friday, 11 March 2011 |
|---|---|
| Origin time | 14:46:23 JST (UTC+09:00) |
| Duration | 6 minutes[1] |
| Magnitude | 9.0 (Mw)[2][3] |
| Depth | 32 km (20 mi) |
| Epicenter | 38°19′19″N 142°22′08″E / 38.322°N 142.369°ECoordinates: 38°19′19″N 142°22′08″E / 38.322°N 142.369°E |
| Type | Megathrust earthquake |
| Countries or regions | Japan (primary) Pacific Rim (tsunami, secondary) |
| Total damage | Tsunami wave, flooding, landslides, fires, building and infrastructure damage, nuclear incidents including radiation releases |
| Max. intensity | IX |
| Peak acceleration | 3.0 g |
| Tsunami | Yes. Up to 40.5 m (133 ft) in Miyako, Iwate, Tōhoku |
| Landslides | Yes |
| Foreshocks | 7 |
| Aftershocks | 1,235 |
| Casualties | 15,850 deaths,[4][5] 6,011 injured,[4][5] 3,287 people missing[4][5] |
The tsunami caused a number of nuclear accidents, primarily the ongoing level 7 meltdowns at three reactors in the Fukushima Daiichi Nuclear Power Plant complex, and the associated evacuation zones affecting hundreds of thousands of residents.[20][21] 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 after cooling system failure. Residents within a 20 km (12 mi) radius of the Fukushima Daiichi Nuclear Power Plant and a 10 km (6.2 mi) radius of the Fukushima Daini Nuclear Power Plant were evacuated. In addition, the U.S. recommended that its citizens evacuate up to 80 km (50 mi) of the plant.[22]
The Japanese National Police Agency confirmed 15,850 deaths,[4][5] 6,011 injured,[4][5] and 3,287 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.[16][23] Japanese Prime Minister Naoto Kan said, "In the 65 years after the end of World War II, this is the toughest and the most difficult crisis for Japan."[24] Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water.[25]
Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion.[26] The Bank of Japan offered ¥15 trillion (US$183 billion) to the banking system on 14 March in an effort to normalize market conditions.[27] The World Bank's estimated economic cost was US$235 billion, making it the most expensive natural disaster in world history.[28][29]
Sendai
Map showing the epicenter of the earthquake
The main earthquake was preceded by a number of large foreshocks, with hundreds of aftershocks reported. The first major foreshock was a 7.2 MW event on 9 March, approximately 40 km (25 mi) from the epicenter of the 11 March earthquake, with another three on the same day in excess of 6.0 MW.[2][33] Following the main earthquake on 11 March, a 7.0 MW aftershock was reported at 15:06 JST (6:06 UTC), succeeded by a 7.4 MW at 15:15 JST (6:16 UTC) and a 7.2 MW at 15:26 JST (6:26 UTC).[34] Over eight hundred aftershocks of magnitude 4.5 MW or greater have occurred since the initial quake.[35] Aftershocks follow Omori's Law, which states that the rate of aftershocks declines with the reciprocal of the time since the main quake. The aftershocks will thus taper off in time, but could continue for years.[36]
One minute before the earthquake was felt in Tokyo, the Earthquake Early Warning system, which includes more than 1,000 seismometers in Japan, sent out warnings of impending strong shaking to millions. It is believed that the early warning by the Japan Meteorological Agency (JMA) saved many lives.[37][38] The warning for the general public was delivered about 8 seconds after the first P wave was detected, or about 31 seconds after the earthquake occurred. However, the estimated intensities were smaller than the actual ones in some places in Kanto and Tohoku regions. This was thought to be because of smaller estimated earthquake magnitude, smaller estimated fault plane, shorter estimated fault length, not having considered the shape of the fault, etc.[39] There were also cases where large differences between estimated intensities by the Earthquake Early Warning system and the actual intensities occurred in the aftershocks and triggered earthquakes.[40]
This earthquake occurred where the Pacific Plate is subducting under the plate beneath northern Honshu; which plate is a matter of debate amongst scientists.[18][41] The Pacific plate, which moves at a rate of 8 to 9 cm (3.1 to 3.5 in) per 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 caused the sea floor to rise by several meters.[41] A quake of this magnitude usually has a rupture length of at least 480 km (300 mi) and generally requires a long, relatively straight fault surface. Because the plate boundary and subduction zone in the area of the rupture 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.[42] The hypocentral region of this earthquake extended from offshore Iwate Prefecture to offshore Ibaraki Prefecture.[43] 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).[44][45] Analysis showed that this earthquake consisted of a set of three events.[46] 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.[47] Other major earthquakes with tsunamis struck the Sanriku Coast region in 1896 and in 1933.
In a study of N. Uchida and T. Matsuzawa, it was pointed out that the source area of this earthquake has a relatively high coupling coefficient surrounded by areas of relatively low coupling coefficients in the west, north, and south. From the averaged coupling coefficient of 0.5~0.8 in the source area and the seismic moment, it was estimated that the slip deficit of this earthquake was accumulated over a period of 260~880 years, which is consistent with the recurrence interval of such great earthquakes estimated from the tsunami deposit data. The seismic moment of this earthquake accounts for about 93% of the estimated cumulative moment from 1926 to March 2011. Hence, earthquakes with magnitudes about 7 since 1926 in this area only had released part of the accumulated energy. In the area near the trench, the coupling coefficient is high, which could act as the source of the large tsunami.[48]
The strong ground motion registered at the maximum of 7 on the Japan Meteorological Agency seismic intensity scale in Kurihara, Miyagi Prefecture.[49] 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.
In Russia, the main shock could be felt in Yuzhno-Sakhalinsk (MSK 4) and Kurilsk (MSK 4). The aftershock at 06:25 UTC could be felt in Yuzhno-Kurilsk (MSK 5) and Kurilsk (MSK 4).[50]
Dam failure at Fujinuma
In the immediate aftermath of the calamity, at least 1.5 million households were reported to have lost access to water supplies.[25][205] By 21 March 2011, this number fell to 1.04 million.[206]
