2011 Tōhoku earthquake and tsunami

• 1. Introduction

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  At 14:46 and 24 seconds on the 11th of March 2011, a force that had been building for hundreds of years finally broke loose beneath the Pacific Ocean, 72 km east of Japan's Oshika Peninsula. The ground shook for approximately six minutes. In Sendai, the nearest major city to the epicenter, residents had only eight to ten minutes of warning before the sea arrived. The earthquake that triggered what followed was the most powerful ever recorded in Japan and the fourth most powerful recorded anywhere in the world since modern seismography began in 1900. What came next would test every system Japan had built to protect itself, and find most of them wanting. How does a disaster of this magnitude unfold? What happens when the sea walls are not tall enough, the warning systems underestimate the threat, and three nuclear reactors begin to melt down at the same time? And who are the people caught in the middle of all of it?

• 2. The Geology of a Giant

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  The magnitude 9.1 rupture was not, geologically speaking, a surprise. The Japan Meteorological Agency's fault zone extended from offshore Iwate Prefecture to offshore Ibaraki Prefecture, a length of 500 km and a width of 200 km. This earthquake was a recurrence of the mechanism behind the 869 Sanriku earthquake, estimated at a magnitude of at least 8.4, which had also generated a large tsunami that flooded the Sendai plain. Three tsunami deposits have been identified within the plain's geological record across the last 3,000 years, pointing to a recurrence interval of 800 to 1,100 years for large tsunamigenic earthquakes. In 2001, researchers reckoned that the probability of a major event was high, since more than 1,100 years had elapsed since the last one. By 2007, scientists placed the probability of a magnitude 8.1-8.3 earthquake within the following 30 years at 99%. The quake's magnitude nevertheless surprised some seismologists. Because the plate boundary in the Honshu rupture zone is not very straight, it is unusual for an earthquake there to exceed magnitude 8.5. What made this event so powerful was the behavior of the Pacific plate, which moves at 8 to 9 cm per year and dips beneath the plate carrying northern Honshu, steadily storing elastic energy until the system snapped. The break raised the sea floor by several meters, displacing an enormous column of water above it. The earthquake initially moved Honshu 2.4 m east, shifted the Earth on its rotational axis by estimates of between 10 and 25 cm, and increased Earth's rotational speed by 1.8 microseconds per day. Off the coast of Miyagi Prefecture, the seabed was later found to have risen by 3 m. A report published in the journal Science in December 2011 concluded that the seabed near the Japan Trench moved 50 m east-southeast and rose about 7 m. A 400 km stretch of Japan's coastline dropped by 0.6 m, a change scientists say is permanent, leaving those communities permanently more exposed to flooding at high tide.

• 3. Warning Systems Under Pressure

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  More than 1,000 seismometers spread across Japan formed the backbone of the Earthquake Early Warning system, and they broadcast an alert to millions of people about one minute before shaking arrived in Tokyo. The warning for the general public was delivered about 31 seconds after the earthquake began, and eight seconds after the first P wave was detected. The Japan Meteorological Agency believes the system saved many lives. But the warning system also made a consequential error. The initial earthquake and tsunami height predictions were based on a calculation that requires only about three minutes of data. That calculation depends on the maximum amplitude of the seismic wave, using a magnitude scale that saturates for earthquakes above magnitude 8. In other words, for very large earthquakes, the scale's values change little despite enormous differences in actual energy released. The result was an initial underestimation of the tsunami's likely height. Residents of Sendai had eight to ten minutes of warning, but the projected wave heights broadcast over mass media led some people to underestimate the danger and either delay or suspend their evacuation. A wave meter reading of "20 cm" was broadcast early, adding to the confusion. The JMA's updated warning was supposed to arrive 15 minutes after the quake, but the strong shaking had exceeded the measurement limit of all teleseismometers within Japan. The second update reached some residents 28 minutes after the earthquake, by which time power failures had cut communications entirely in some areas. A study found that 58% of people in coastal areas of Iwate, Miyagi, and Fukushima heeded the tsunami warnings immediately and headed for higher ground. Of those who tried to evacuate after hearing the warning, only five percent were caught by the water. Of those who ignored the warning, 49% were hit. At least 101 designated tsunami evacuation sites were washed away. JMA began an investigation in 2011 and updated their warning system in 2013. Under the new rules, for a quake powerful enough to saturate the JMA magnitude scale, no quantitative prediction is released in the initial warning; instead, the system issues words describing the emergency.

• 4. The Wave

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  An upthrust of 6 to 8 m along a 180 km-wide section of seabed, 60 km offshore, generated the tsunami that devastated Japan's Pacific coastline. At Sendai Airport, at 15:55 JST, the water swept away cars and planes. An NHK News helicopter filmed vehicles on local roads attempting to escape and being swallowed. The GOCE satellite in low orbit inadvertently became the first seismograph in orbit when it detected infrasound waves generated by the earthquake. The tsunami reached heights of up to 40.5 m in Miyako. At Ryori Bay in Ofunato, the run-up elevation was 40.1 m, and fishing equipment was later found scattered on the cliff above. At the slope of a mountain near Aneyoshi fishery port on the Omoe peninsula in Miyako, the run-up height was estimated at 38.9 m, which was cited as a record in Japan, exceeding the 38.2 m from the 1896 Sanriku earthquake. At Rikuzentakata, the wave reached three stories high. In the Sendai area, waves traveled at 700 km/h and pushed up to 10 km inland. The inundated area in Japan totaled approximately 561 km2. The most severe destruction along Japan's coast ran for 670 km, from Erimo in Hokkaido in the north to Oarai in Ibaraki in the south, with most of the damage occurring in the hour after the earthquake. The sea walls had been built to protect against tsunamis of much lower heights; some were simply overtopped, others collapsed. Chile's Pacific coast, approximately 17,000 km from Japan, was struck by waves 2 m high. A 1.5 m wave submerged Midway Atoll's reef inlets and Spit Island, killing more than 110,000 nesting seabirds at the Midway Atoll National Wildlife Refuge. The tsunami broke icebergs from the Sulzberger Ice Shelf in Antarctica, 13,000 km away; the main iceberg measured approximately 9.5 by 6.5 km and was about 80 m thick, and a total of 125 km2 of ice broke away.

• 5. The Human Cost

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  Ishinomaki, the city with the most deaths, recorded a temperature of 0 degrees Celsius when the tsunami hit, and snow began to fall within hours. The cold and the snow hampered rescue efforts across the region. Official figures released in 2021 counted the full scale of the losses. Drowning accounted for 90.64% of deaths. Elderly people aged over 60 made up 65.8% of all deaths. The deadliest prefectures were Miyagi with 10,567 deaths, Iwate with 5,145, and Fukushima with 3,920. A report in 2015 found that 228,863 people were still living away from their homes, either temporarily or permanently. Japanese funerals are normally elaborate Buddhist ceremonies involving cremation. The thousands of bodies exceeded the capacity of available crematoriums and morgues, many of them damaged. There were shortages of both kerosene, with each cremation requiring 50 litres, and dry ice for preservation. The single crematorium in Higashimatsushima could handle only four bodies a day, although hundreds were found in the town. Governments and the military were forced to bury many bodies in hastily dug mass graves with little or no ceremony, with relatives promised later cremation. At Okawa Elementary School in Ishinomaki, 74 of 108 students and 10 of 13 teachers died in the tsunami, the result of poor decision-making during evacuation. Save the Children reported that as many as 100,000 children were uprooted from their homes. A total of 236 children were orphaned across Iwate, Miyagi, and Fukushima, and 1,580 children lost one or both parents. The Japanese Foreign Ministry confirmed the deaths of 19 foreigners, including two English teachers from the United States affiliated with the Japan Exchange and Teaching Program and a Canadian missionary in Shiogama. 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."

• 6. Fukushima and the Nuclear Crisis

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  The Fukushima Daiichi Nuclear Power Plant sits on Japan's Pacific coast, and when tsunami waves overtopped the sea walls, they destroyed the diesel backup power systems. Without electricity, cooling systems halted, heat built, and hydrogen gas accumulated within the upper refueling hall and exploded, forcefully ejecting the blast panels. Three of Fukushima Daiichi's reactors suffered meltdowns. Residents within 20 km of Fukushima Daiichi and within 10 km of Fukushima Daini were evacuated. Radiation levels inside the plant were reported by the Japanese Nuclear and Industrial Safety Agency to be up to 1,000 times normal levels, and outside the plant up to eight times normal levels. Radioactive iodine was detected in tap water in Fukushima, Tochigi, Gunma, Tokyo, Chiba, Saitama, and Niigata. Radioactive caesium was detected in the soil in some places in Fukushima. Many radioactive hotspots were found outside the evacuation zone, including in Tokyo. Experts assessed the Fukushima disaster as worse than the Three Mile Island accident but not as bad as Chernobyl. The aftershock on the 7th of April also caused the loss of external power to Rokkasho Reprocessing Plant and Higashidori Nuclear Power Plant, though backup generators at those sites remained functional. In 2013, only two nuclear reactors in Japan had been restarted since the 2011 shutdowns. In February 2019, of Japan's 42 operable reactors, only nine in five power plants were operating after being restarted post-2011. In 2021, the Japanese cabinet approved the release of treated radioactive water into the Pacific Ocean over 30 years, a process scheduled to be completed by 2051. The Fukushima nuclear crisis also created a power emergency for the broader region: TEPCO's total capacity was reduced by 21 GW, and rolling blackouts began on the 14th of March 2011 across Tokyo, Kanagawa, Chiba, Ibaraki, Saitama, and several other prefectures.

• 7. Recovery and Memory

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  754 cultural properties were damaged across 19 prefectures in the disaster, including five National Treasures at sites such as Zuigan-ji and Osaki Hachiman-gu, and 160 Important Cultural Properties. Stone monuments at the UNESCO World Heritage Site of the Shrines and Temples of Nikko were toppled. The estimated economic damage amounted to over $300 billion, making it the costliest natural disaster in history to that point. The Bank of Japan offered 15 trillion yen to the banking system on the 14th of March 2011 to normalize market conditions. A 2020 study found that the earthquake and its aftermath resulted in a 0.47 percentage point decline in Japan's real GDP growth in the year following the disaster. The reconstruction was funded and directed by the Japanese government, with structural adaptation largely based on building higher sea walls. A special government committee noted that the tsunami protection policy before 2011 had been designed only for tsunamis scientifically proven to recur repeatedly; the committee advised that future policy should account for the highest possible tsunami. In Ishinomaki alone, there were 17 trash collection sites each 180 m long and at least 4.5 m high; a city official estimated it would take three years to empty them. The Japanese Ministry of the Environment estimated the disaster produced 5 million tonnes of waste. In April 2015, debris thought to be from a tsunami-destroyed boat was discovered off the coast of Oregon, still carrying yellowtail amberjack, a species that lives off Japan's coast, alive. In February 2016, a memorial was inaugurated for the disaster's victims: a 6.5 m2 structure on a hillside between a temple and a cherry tree in Ishinomaki. A report published by Japan's National Police Agency in September 2018 listed 121,778 buildings as totally collapsed, with a further 280,926 half collapsed and 699,180 partially damaged.