Key figures: Prime Minister Naoto Kan, Japan Meteorological Agency (JMA), Japan Self-Defense Forces, Tokyo Electric Power Company (TEPCO), Reconstruction Agency
Summary
On March 11, 2011, at 14:46 Japan Standard Time, a magnitude 9.0 undersea megathrust earthquake struck off the Pacific coast of the Tōhoku region of north-eastern Honshu, Japan. Known in Japan as the Great East Japan Earthquake (Higashi Nihon Daishinsai), it was the most powerful earthquake ever recorded in Japan and the fourth most powerful recorded anywhere in the world since modern instrumental seismography began around 1900. The United States Geological Survey later revised its estimate of the moment magnitude to 9.1. The rupture occurred where the Pacific Plate subducts beneath the plate underlying northern Honshu, with an epicentre approximately 70 kilometres east of the Oshika Peninsula at a depth of about 29 kilometres, and the ground shook for roughly six minutes.
The earthquake generated a catastrophic tsunami that reached run-up heights of up to roughly 40 metres at Miyako in Iwate Prefecture and travelled as far as 10 kilometres inland across the low-lying Sendai plain. The waves overtopped seawalls, swept away entire coastal communities, and disabled the cooling systems of the Fukushima Daiichi Nuclear Power Plant, triggering a separate nuclear crisis. The combined disaster killed roughly 18,500 people, displaced hundreds of thousands more, and became the costliest natural disaster in recorded history.
The Earthquake
The Tōhoku earthquake was a megathrust event along the Japan Trench, where the Pacific Plate descends beneath the Okhotsk Plate. The rupture extended roughly 500 kilometres in length and 200 kilometres in width, and the seafloor was displaced by tens of metres — movement that displaced the enormous volume of water responsible for the tsunami. The shaking was felt across most of Honshu and registered the maximum level of 7 on the Japan Meteorological Agency’s shindo seismic-intensity scale in northern Miyagi Prefecture.
The earthquake’s geophysical effects were measurable on a planetary scale. It shifted the main island of Honshu approximately 2.4 metres eastward, moved the Earth’s figure axis by an estimated 10 to 25 centimetres, and is calculated to have shortened the length of the day by about 1.8 microseconds by redistributing the planet’s mass. More than 5,000 aftershocks followed in the months afterward, several exceeding magnitude 7.
The Tsunami
The first tsunami waves reached the Tōhoku coast within roughly 30 minutes of the earthquake. The Japan Meteorological Agency issued its highest-level tsunami warning within minutes, but the speed and height of the waves overwhelmed coastal defences that had been engineered for smaller events. In communities such as Rikuzentakata, Minamisanriku, and Ōtsuchi, the waves destroyed the great majority of buildings and killed substantial fractions of the local population. The water surged over the 10-metre seawall protecting parts of the Sendai plain and inundated farmland, airports, and towns.
The tsunami also propagated across the entire Pacific Ocean, prompting warnings and evacuations as far away as Hawaii, the west coast of the Americas, and the Pacific coast of Chile, where waves of more than two metres were recorded. In Antarctica, the tsunami is thought to have helped calve icebergs from the Sulzberger Ice Shelf.
Casualties and Displacement
The National Police Agency of Japan confirmed approximately 15,900 deaths, with around 2,500 people still listed as missing and presumed dead, for a direct toll of roughly 18,400 to 18,500. The overwhelming majority — more than 90 percent — drowned, and a disproportionate number of the dead were elderly. Thousands more “disaster-related deaths” were subsequently attributed to the physical and psychological strain of prolonged evacuation, particularly among displaced and older residents.
At the peak of the emergency, more than 470,000 people were evacuated from coastal areas and from the exclusion zone around the Fukushima Daiichi plant. The disaster damaged or destroyed well over a million buildings, severed road, rail, and power networks across the region, and left survivors in emergency shelters for months.
Economic Impact and Reconstruction
The Japanese government estimated direct damage at approximately ¥16.9 trillion (on the order of US$200 billion), while the World Bank put the total economic cost at around US$235 billion — figures widely cited as making the Tōhoku disaster the costliest natural disaster in recorded history. The shock disrupted global supply chains, particularly in the automotive and electronics industries that depended on components manufactured in the affected region, and contributed to a contraction in Japanese industrial output in 2011.
In February 2012, the government established a dedicated Reconstruction Agency to coordinate the decade-long rebuilding of the Tōhoku coast, funded by a multi-year reconstruction budget and special taxes. Recovery proved slow and uneven: seawalls were rebuilt taller, some communities were relocated to higher ground, and the depopulation of the region accelerated as younger residents moved away.
Significance
The Tōhoku earthquake and tsunami reshaped Japanese and global thinking about disaster risk, coastal engineering, and nuclear safety. The failure of seawalls designed for historically observed tsunamis prompted a reassessment of “maximum credible” event planning and a shift toward defence-in-depth strategies combining physical barriers, evacuation, and land-use planning. The disaster’s destruction of the Fukushima Daiichi plant’s backup power triggered the worst nuclear accident since Chernobyl, drove Japan to idle its entire nuclear fleet for safety reviews, and accelerated nuclear-policy debates in Germany and elsewhere.
The catastrophe also became a defining test of disaster response and resilience. Japan’s early-warning systems, building codes, and public preparedness were widely credited with limiting earthquake-shaking deaths, even as the tsunami exposed the limits of coastal protection. March 11 became a national day of mourning, and the phrase “Great East Japan Earthquake” entered common use for one of the defining events of 2011.
Sources
- 2011 Tōhoku earthquake and tsunami — Wikipedia
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[Japan earthquake and tsunami of 2011 Facts & Death Toll — Britannica](https://www.britannica.com/event/Japan-earthquake-and-tsunami-of-2011) - On This Day: 2011 Tohoku Earthquake and Tsunami — NOAA National Centers for Environmental Information
- Tohoku Earthquake and Tsunami — National Geographic Education