The 2011 earthquake off the Pacific coast of Tōhoku was a magnitude 9.0–9.1 (Mw) undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC) on Friday 11 March 2011, with the epicentre approximately 70 kilometres (43 mi) east of the Oshika Peninsula of Tōhoku and the hypocenter at an underwater depth of approximately 29 km (18 mi). The earthquake is often referred to in Japan as the Great East Japan Earthquake (東日本大震災 Higashi nihon daishinsai) and is also known as the 2011 Tōhoku earthquake and the 3.11 earthquake.
It was the most powerful earthquake ever recorded in Japan, and the fourth most powerful earthquake in the world since modern record-keeping began in 1900. The earthquake triggered powerful tsunami waves that may have reached heights of up to 40.5 meters (133 ft) in Miyako in Tōhoku's Iwate Prefecture, and which, in the Sendai area, traveled up to 10 km (6 mi) inland.
The earthquake moved Honshu (the main island of Japan) 2.4 m (8 ft) east, shifted the Earth on its axis by estimates of between 10 cm (4 in) and 25 cm (10 in), increased earth's rotational speed by 1.8 µs per day, and generated infrasound waves detected in perturbations of the low-orbiting GOCE satellite. Initially, the earthquake caused the sinking of part of Honshu's Pacific coast by up to roughly a meter, but after about three years, the coast rose back and kept on rising to exceed its original height.
The tsunami swept the Japanese mainland and killed over ten thousand people, mainly through drowning, though blunt trauma also caused many deaths. The latest report from the Japanese National Police Agency report confirms 15,896 deaths, 6,157 injured, and 2,537 people missing across twenty prefectures, and a report from 2015 indicated 228,863 people were still living away from their home in either temporary housing or due to permanent relocation.
A report by the National Police Agency of Japan on 10 September 2018 listed 121,778 buildings as "total collapsed", with a further 280,926 buildings "half collapsed", and another 699,180 buildings "partially damaged". The earthquake and tsunami also caused extensive and severe structural damage in north-eastern Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse. 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." Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water.
The tsunami caused nuclear accidents, primarily the 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. 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 resulting from the loss of electrical power. 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.
Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion. The Bank of Japan offered ¥15 trillion (US$183 billion) to the banking system on 14 March in an effort to normalize market conditions. The World Bank's estimated economic cost was US$235 billion, making it the costliest natural disaster in history.
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