Tohoku Earthquake and Tsunami (2011): Japan's Great Disaster

The Tohoku earthquake and tsunami struck north-eastern Japan on 11 March 2011, when a magnitude 9.0-9.1 earthquake beneath the Pacific seabed sent a tsunami crashing onto the coast of the Tohoku region. Known in Japan as the Great East Japan Earthquake, it killed about 18,000 people, most of them by drowning, and destroyed entire coastal towns. It was the most powerful earthquake in Japan’s recorded history and one of the costliest natural disasters ever, and it also triggered the Fukushima Daiichi nuclear disaster, which this article treats only briefly.

Background: a coast built on a subduction zone

Japan sits where several tectonic plates meet. Off the Tohoku coast, the Pacific Plate moves westward by about 8-9 centimetres a year and dives beneath the plate carrying northern Honshu along a deep seabed trough called the Japan Trench. Where one plate slides under another, the two can lock together for centuries before slipping suddenly in a “megathrust” earthquake.

The Sanriku coast of Iwate and Miyagi prefectures, with its deep, narrow bays, had a long history of tsunamis. The Meiji Sanriku tsunami of 1896 killed about 22,000 people, and the Showa Sanriku tsunami of 1933 killed about 3,000. Geologists had also found sand layers left by the Jogan tsunami of AD 869, which had flooded far inland across the Sendai plain.

Japan was probably the best-prepared country in the world for earthquakes. Strict building codes had been tightened after the Kobe earthquake of 1995, and many coastal towns had sea walls and evacuation routes. Official hazard planning, however, generally assumed earthquakes of magnitude 7.5-8.5 on separate sections of the trench, not a single rupture covering hundreds of kilometres.

The earthquake of 11 March

The earthquake began at 2:46 p.m. local time (05:46 UTC) about 70 kilometres east of the Oshika Peninsula and roughly 130 kilometres east of the city of Sendai, at a depth of about 25-30 kilometres. A magnitude 7.2-7.3 foreshock had struck in the same area two days earlier, on 9 March.

The rupture spread along the Japan Trench for some 400-500 kilometres and over a width of about 150-200 kilometres. Near the trench, the seafloor slipped by as much as 50 metres, the largest fault slip ever measured. Shaking lasted for several minutes and reached the top of Japan’s intensity scale, shindo 7, in Kurihara, Miyagi Prefecture. In Tokyo, about 370 kilometres from the epicentre, skyscrapers swayed and the transport system stopped.

Japan’s earthquake early warning system sent alerts to television and mobile phones seconds before the strongest shaking arrived, and high-speed Shinkansen trains braked automatically. Because of the strict building codes, relatively few modern buildings collapsed from shaking alone. The main killer was still to come.

The tsunami

The sudden uplift of the seabed displaced an enormous volume of water. The first large waves reached parts of the coast within about 20-30 minutes; in some places they arrived even sooner. The Japan Meteorological Agency issued its highest tsunami warning within three minutes, but its first estimates of wave height, 3-6 metres, proved far too low and were raised only as the waves approached.

Along the ria coast of Iwate, the narrow bays funnelled the water upward. Survey teams later measured run-up heights of 10-20 metres along much of the Sanriku coast and a maximum of about 40 metres near Miyako. On the flat Sendai plain, the tsunami was lower but pushed up to 5-6 kilometres inland, flooding Sendai Airport and farmland. In total about 560 square kilometres of land was inundated.

Sea walls failed or were overtopped in many towns. In the Taro district of Miyako, a double sea wall about 10 metres high, once nicknamed the “Great Wall”, was overwhelmed. In Rikuzentakata, most of the town centre was swept away; of a coastal forest of some 70,000 pine trees, a single tree survived, becoming a national symbol before it died of salt damage and was preserved as a monument. In Minamisanriku and Onagawa, waves rose above three- and four-storey buildings designated as refuges.

One of the most painful losses came at Okawa Elementary School in Ishinomaki, where 74 of the 108 pupils and 10 teachers were killed after the school delayed evacuation to higher ground. Courts later found the local authorities liable, and the case led to new rules on school disaster planning.

The tsunami spread across the Pacific. Waves several metres high reached Hawaii and the west coast of the Americas, damaging harbours such as Crescent City in California. One man was killed in northern California and one in Papua, Indonesia.

Casualties and damage

According to Japan’s Fire and Disaster Management Agency, about 15,900 people were confirmed dead and around 2,500 remain missing. More than 90 percent drowned, and over half of the dead were aged 65 or older, many of whom could not move quickly enough to escape. Miyagi Prefecture suffered the most deaths, followed by Iwate and Fukushima.

A further 3,700 or so “disaster-related deaths” were later recognised, mainly among elderly evacuees who died from illness, stress or interrupted medical care in the months and years after the disaster. Including these, the total exceeds 19,000.

More than 120,000 buildings were completely destroyed and over 280,000 half-destroyed. At the peak, around 400,000-470,000 people were living in evacuation centres. Roads, railways, ports and fishing fleets were wrecked, and the Japanese government estimated direct damage at about 16.9 trillion yen (roughly 200 billion US dollars at the time), excluding the nuclear accident. The World Bank put the overall economic cost as high as 235 billion US dollars, making it the costliest natural disaster on record at that time.

The earthquake also changed the shape of the land. Parts of north-eastern Honshu moved up to about 5 metres eastward, and stretches of coast sank by up to about 1 metre, leaving some areas permanently more exposed to flooding.

The nuclear accident and the national response

The tsunami flooded the Fukushima Daiichi nuclear power plant, run by the Tokyo Electric Power Company (TEPCO), knocking out its backup diesel generators. Without cooling, three reactors melted down and hydrogen explosions followed between 12 and 15 March. Tens of thousands of people were evacuated from zones around the plant. The accident, rated at the maximum level 7 on the international scale like the Chernobyl disaster, is covered in its own article.

Prime Minister Naoto Kan’s government mobilised about 100,000 members of the Self-Defense Forces, nearly half the entire force, for rescue and relief. The United States military joined through Operation Tomodachi (“friend”), and rescue teams arrived from more than 20 countries. On 16 March Emperor Akihito addressed the nation in an unprecedented televised message, expressing concern for the victims and encouraging the rescuers.

Power shortages led to rolling blackouts in the Tokyo area, and damage to factories in Tohoku disrupted global supply chains for car parts and electronics for months.

Recovery and reconstruction

Japan created a Reconstruction Agency in February 2012 and committed about 32 trillion yen to reconstruction over the following decade. Hundreds of thousands of people lived for years in prefabricated temporary housing. Towns such as Rikuzentakata and Onagawa raised the ground level of their centres by several metres using huge quantities of earth, while homes were rebuilt on higher ground.

A new chain of sea walls, totalling roughly 400 kilometres and in places more than 14 metres high, was built along the Tohoku coast. The walls were controversial: some residents welcomed the protection, while others regretted losing their view of the sea and argued that evacuation, not concrete, saves lives.

Many coastal communities did not recover their former populations. Young people moved to the cities, fishing and farming took years to resume, and some areas near the Fukushima plant remained closed for more than a decade.

Lessons and legacy

The disaster showed that planning based on the largest earthquakes of the past few centuries could badly underestimate the risk. Japanese authorities revised their hazard models to consider the largest possible earthquakes and tsunamis, not only the most likely. The tsunami warning system was redesigned so that, for very large earthquakes, it announces “huge” waves immediately rather than giving low early numbers.

Stories of survival also reinforced old local wisdom. In the hamlet of Aneyoshi near Miyako, a stone tablet erected after the 1933 tsunami warned residents not to build homes below it; the water stopped just short of the marker. The Sanriku tradition of “tsunami tendenko”, meaning that each person should flee to high ground at once without waiting for others, became a key part of disaster education.

Together with the Indian Ocean tsunami of 2004, the 2011 disaster transformed scientific understanding of megathrust earthquakes and showed that even wealthy, well-prepared societies remain vulnerable to the largest natural hazards.

By the numbers

Timeline

• 869, July: The Jogan earthquake and tsunami flood the Sendai plain, a precedent later uncovered by geologists.
• 1896, 15 June: The Meiji Sanriku tsunami kills about 22,000 people on the same coast.
• 2011, 9 March: A magnitude 7.2-7.3 foreshock strikes off Miyagi.
• 2011, 11 March: At 2:46 p.m. the magnitude 9.0-9.1 earthquake strikes; tsunami waves reach the coast within about 20-30 minutes.
• 2011, 12-15 March: Explosions and meltdowns occur at the Fukushima Daiichi nuclear plant.
• 2011, 16 March: Emperor Akihito addresses the nation on television.
• 2012, 10 February: Japan’s Reconstruction Agency is established.
• 2021, 11 March: Japan marks the tenth anniversary as the main reconstruction period draws to a close.

Why it matters

The Tohoku earthquake and tsunami was Japan’s worst disaster since the Second World War and one of the deadliest tsunamis in history. It exposed the limits of even the most advanced preparations, reshaped disaster planning in Japan and worldwide, and, through the Fukushima accident, changed global debates about nuclear power.