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yThe 9.1 magnitude (Mw) undersea megathrust earthquake occurred on 11 March 2011 at 14:46 in the north-western Pacific Ocean at a relatively shallow depth of 32 km with its epicenter approximately  (45 mi) east of the Oshika Peninsula of Tohoku, Japan, lasting approximately six minutes.[1][7] The earthquake was initially reported as 7.9 Mw by the USGS before it was quickly upgraded to 8.8 Mw, then to 8.9 Mw,[52] and then finally to 9.0 Mw.[8][53] Sendai was the nearest major city to the earthquake, 130 km (81 mi) from the epicenter; the earthquake occurred 373 km (232 mi) from Tokyo.[7] One of the first major foreshocks was a 7.2 Mw event on 9 March, approximately 40 km (25 mi) from the epicenter of 11 March earthquake, with another three on the same day in excess of 6.0 Mw.[7][54] Following the main earthquake on 11 March, a 7.4 Mw aftershock was reported at 15:08 JST (6:06 UTC), succeeded by a 7.9 Mw at 15:15 JST (6:16 UTC) and a 7.7 Mw at 15:26 JST (6:26 UTC).[55] Over eight hundred aftershocks of magnitude 4.5 Mw or greater have occurred since the initial quake,[56] including one on 26 October 2013 (local time) of magnitude 7.1 Mw.[57] Aftershocks follow Omori's Law, which states that the rate of aftershocks declines with the reciprocal of the time since the main quake.

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Portions of northeastern Japan shifted by as much as 2.4 metres (7 ft 10 in) closer to North America,[33][34] making some sections of Japan's landmass wider than before.[34] Those areas of Japan closest to the epicenter experienced the largest shifts.[34] A 400-kilometre (250 mi) stretch of coastline dropped vertically by 0.6 metres (2 ft 0 in), allowing the tsunami to travel farther and faster onto land.[34] One early estimate suggested that the Pacific plate may have moved westward by up to 20 metres (66 ft),[83] and another early estimate put the amount of slippage at as much as 40 m (130 ft).[84] On 6 April the Japanese coast guard said that the quake shifted the seabed near the epicenter 24 metres (79 ft) and elevated the seabed off the coast of Miyagi Prefecture by 3 metres (9.8 ft).[85] A report by the Japan Agency for Marine-Earth Science and Technology, published in Science on 2 December 2011, concluded that the seabed in the area between the epicenter and the Japan Trench moved 50 metres (160 ft) east-southeast and rose about 7 metres (23 ft) as a result of the quake.

The Earth's axis shifted by estimates of between 10 cm (4 in) and 25 cm (10 in).[33][34][35] This deviation led to a number of small planetary changes, including the length of a day, the tilt of the Earth, and the Chandler wobble.[35] The speed of the Earth's rotation increased, shortening the day by 1.8 microseconds due to the redistribution of Earth's mass.[87] The axial shift was caused by the redistribution of mass on the Earth's surface, which changed the planet's moment of inertia.

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Japan's National Research Institute for Earth Science and Disaster Prevention (NIED) calculated a peak ground acceleration of 2.99 g (29.33 m/s2).[79][fn 2] The largest individual recording in Japan was 2.7 g, in Miyagi Prefecture, 75 km from the epicentre; the highest reading in the Tokyo metropolitan area was 0.16 g.[82]

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However, while the tsunami affected many of these places, the extent was minor.[109][110][111] Chile's Pacific coast, one of the furthest from Japan at about 17,000 km (11,000 mi) distant, was struck by waves 2 m (6.6 ft) high,[112][113][114] compared with an estimated wave height of 38.9 metres (128 ft) at Omoe peninsula, Miyako city, Japan.[31

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Victims aged 60 or older accounted for 65.2% of the deaths, with 24% of total victims being in their 70s.[189] As of March 2012, Japanese police data showed that 70% of the 3,279 still missing were aged 60 or over, all found, including 893 in their 70s and 577 in their 80s.

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JAPAN - The Earthquake - 15 Minutes Live-Cam

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(2011) Hear an eyewitness describe Japan's 8.9 magnitude earthquake