Is another massive tsunami imminent in Japan?

Fourteen years ago, Japan was devastated by one of the deadliest tsunamis in modern history. Now a prophetic manga is fueling anxiety of a repeat. Could such a calamity occur soon again?

On Friday, March 11, 2011, at 14:46 hrs, disaster struck Japan. One of the largest earthquakes—officially the Great East Japan Earthquake—on record (magnitude 9.0) occurred just off the northeast Pacific coast of the main island of Honshu. The shaking lasted for a full five minutes—a terrifyingly long time when one entirely loses orientation, may not be able to stand up, with everything falling around you, walls and houses crumbling, the rumble of the earth drowning all other sounds—triggering a massive tsunami. Because the epicenter was so close to the coast, there was hardly any warning or time to evacuate. The first waves reached the Sanriku coast in the Miyagi and Iwate Prefectures within ten minutes, completely overrunning the towns and ports leaving total destruction in their wake. Up to 18,500 people perished. The tsunami also caused the meltdown of the nuclear power plant in Fukushima, Miyagi Prefecture, the worst nuclear accident ever to hit Japan and the worst in the world only after Chernobyl.

Now some people, are again fearful to visit Japan. This is because of a manga comic, published in 1999 and re-released in 2021, warns of a catastrophe hitting Japan in July 2025. The only reason why this comic might scare people off is that it originally predicted, correctly it turned out, a major disaster in Japan in March 2011. The Future I Saw, by the artist Ryo Tatsuki, imagines a massive tsunami caused by a rupture in the undersea fault line between the Philippine and Eurasian plates. As a consequence, the number of tourists, especially from China and Hong Kong, has dropped significantly and some people have decided to postpone their trips to Japan. Tatsuki herself says that she is no prophet.

The scenario itself is not entirely unrealistic. Tsunamis are triggered by undersea events, most often large earthquakes at fault zones, but sometimes by volcanic eruptions or massive landslides deep in the ocean. The Pacific Rim where Japan is located is seismically highly active. The Sanriku Tsunami was the fifth most deadly in the past two centuries or so. The deadliest of all was the Indian Ocean Tsunami on Boxing Day of 2004 when an estimated 230,000-280,000 people perished in half a dozen countries surrounding the Indian Ocean. This was the second time the Sanriku coast was devastated by a tsunami: on June 15, 1896, another tsunami killed some 22,000 people in the same area with waves reaching the height of 30 meters.

Tsunamis are so deadly because of the massive amounts of water and the speed at which they travel. In deep water, the waves remain low but they spread fast in all directions from the epicenter. Tsunami waves have been measured to move at 800 km/h. As they approach shallower coastal waters they slow down, condense, and rise to frightening heights.

This is what destroyed so much of the Sanriku coast. Kesennuma, a port in Miyagi, was gone. I have visited the town both before and after the disaster. First the tsunami swept across the entire low-lying valley. When it receded, fires that ensued as gas pipelines were destroyed finished the job burning down the entire old wooden town. Kesennuma port had been the center of the Pacific shark fisheries just because of the shape of its natural harbor. Now this same geographic advantage had provided the tsunami with a perfect entrance to the harbor bowl allowing the water to rise unhindered into the town.

Tohoku’s largest city, Sendai, situated on higher ground and away from the sea was largely spared from major damage. The city airport closer to the coast was not so lucky. Cameras showed the massive wave sweeping slowly across the runways. Large jet planes floated away like toy models. Aerial shots from the close by mountain areas showed huge liquefaction of the soil, again in slow motion, wiping away entire villages, houses crumbling and washing down the slopes into the sea. 

So what are the chances that such a disaster repeats itself in the near future, if not later this month? It is impossible to give a precise answer to that question. Statistically, major tsunamis globally take place about twice in a decade. The likelihood of one striking a specific major urban is low but it is plausible that one of the major cities around the Pacific Ring of Fire will be struck by a large tsunami in the coming few decades.

The cities most at risk include the Tokyo-Yokohama conurbation, the largest city complex in the world with over 40 million inhabitants. This is also Japan’s economic heart, so a major disaster there would be highly destructive for the country and would disrupt the entire world economy.

Other likely targets include Manila and Jakarta on the Asian side, and Lima and Santiago de Chile in South America, as well as Los Angeles and San Francisco in California. Honolulu in the middle of the Ring of Fire is also vulnerable. In fact, all of these cities have in the past experienced disruptive earthquakes and tsunamis.

Indonesia and its capital Jakarta are particularly at risk from a repeat of an event like the 2004 earthquake and tsunami. Another risk is posed by the active volcano, Krakatoa. Its violent eruption caused a massive tsunami on August 27, 1883. It destroyed two-thirds of the island and killed some 36,000 people, making it the second deadliest event in recorded history.

Hawai’i due to its location has experienced three tsunamis claiming lives in the past eight decades. The worst one was on April 1, 1946, when a 8.6 magnitude earthquake in the Aleutian Islands sent a tsunami racing across the ocean. It destroyed most of Hilo on the Big Island, killing 159 people. As the earthquake that instigated the tsunami took place in Alaska thousands of kilometers northeast of Hawai’I, no one was prepared when the huge waves washed into the islands in the middle of the Pacific Ocean.

When the 9.5 magnitude—the strongest ever recorded—earthquake hit Chile on May 23, 1960, Hilo, 10,000 km away from the epicenter, was again collateral damage and 63 people died there (the range of the casualties overall varies significantly, from 1,000 to 6,000). On November 29, 1979, a local 7.7 magnitude earthquake shook the Big Island causing two deaths. Such a locally generated tsunami gives hardly any warning time for people to escape.

All of the cities exposed to high tsunami risk are constantly monitoring the situation. Japan, with its multi-hazard risk and frequent earthquakes (in fact, a 5.5 magnitude earthquake shook the southwestern Kagoshima Prefecture while I am writing this on the 3rd of July), is arguably the best prepared country in the world. In this, it is helped by its advanced technologies and well-educated, self-disciplined population. Japan employs a national earthquake and tsunami early warning system operated by the Japan Meteorological Agency. It informs people of impending danger through sirens and phone alerts. It has recently deployed drones on the sea in front of popular beaches for tsunami detection. Detailed evacuation maps are maintained by local governments down to the neighborhood level.

Furthermore, millions of people in the country participates in drills and education sessions. September 1st is the National Disaster Prevention Day, with the date commemorating the Great Kantō Earthquake that destroyed Tokyo in 1923.

Scientists in Japan give an 80 percent chance for a mega-quake taking place along the Nankai Trough in the coming 30 years. This revised assessment has led the authorities to require municipalities and businesses to enhance their preparedness plans, to strengthen building earthquake resistance, stockpile food and other necessities, and to update evacuation plans.

Earthquakes and tsunamis cannot be predicted with any degree of certainty. A major event is certain to cause significant damage to infrastructure and the economy. The death of thousands of people in such eventuality is unavoidable. The best we can do is to be aware of the risks and be well prepared. That is our best chance of saving lives.

[Originally published on https://juhauitto.substack.com on July 4, 2025.]

Rikuzentakata July 2015 - Reconstruction from the Tsunami

The earthworks are simply mind blowing. 24-7, the conveyor belts bring earth from the nearby mountains and pile it on the coastal zone to raise the level of the low-lying land by at least 10 meters. It’s more than four years since the tsunami leveled the Sanriku coast and killed more than 15,000 people and made 230,000 homeless on Japan’s Pacific coast. This rehabilitation work that shows virtually no end is a demonstration of Japanese spirit and tenacity.

I traveled back to the Sanriku coast together with Abetake-sensei to see the progress in reconstruction. We did our first jointtrip here in March 2012, just a year after the great east Japan earthquake and tsunami had laid waste to the most unexpecting part of Japan. Abetake-sensei is my wife’s high school geography teacher in Mizusawa, in Iwate Prefecture.

Mizusawa is luckily some 60 km inland and higher up in elevation from the coast. Although the earthquake affected my family’s area, the tsunami did not reach even close.

Abetake-sensei picked me up in Mizusawa this rainy morning and we crossed the coastal mountain range to reach the Sanriku coast. The rather high limestone mountains have all their steep slopes covered in thick forest. In odd flat locations one can suddenly see perfectly maintained rice paddies on terraces where the terrain has allowed adequate space. At this time of the year, their green is so bright as to shine amongst the dark hills. The rainy season – tsuyu – is supposed to be over but the rain has been heavy since last night.

We stopped at Daitoo, a town about half way to the coast for a rest stop and a cigarette for my host. Daitoo is in a beautiful spot in a valley protected from all sides by mountains. We continued onwards driving through the village of Ohara, a small agricultural congregation by the Satetsugawa river, a tributary to the Kitagamigawa river that flows from the north to the south traversing Mizusawa. We were still on the western side of the watershed, meaning that the river flows inland towards the more major Kitagamikawa river.

Having soon crossed the next range – through some distinctly impressive bridges and tunnels above and through mountains – we started descending to the coastal plain. At this stage the road followed Kesengawa, a charming if not a major river known for its Ayu fisheries (ayu or sweetfish caught in rivers and often grilled or fried is one of the delicacies of the Tohoku region). The Kesengawa drains into the Pacific Ocean and when the tsunami struck, its flow was reversed bringing the devastating flood waters as far as 7 km inland.

Descending onto the coastal plain past the sea terraces, the landscape had changed so much that it was difficult to get one’s bearings. On both sides of the road there were huge mounds of earth leveled by bulldozers while enormous conveyer belts transported more earth to the piles from the nearby mountains. It seemed that the goal was to raise the level of the entire coastal plain by 10 meters. For what purpose, was not imminently clear. Hundreds of men and machines were at work now more than four years after the tragedy.

Access to the coastline was blocked from the main area of the former town. We drove south towards Kesennuma and found a road that led to the fishing port. Even there men were at work establishing seawalls. Still, I was able to get to the waterfront to observe the bay where boats were again active.

The legendary lone pine – Ippon Matsu – that became the symbol of resilience after the tsunami is long gone. It was one in many tall pines that lined the coast and miraculously survived the tidal wave – but despite the efforts of the city officials, scientists and the public, it died because of the salinization of the soil and groundwater after the intrusion of the sea. It lives on in numerous flags and posters and a monument is being established for it, I was told although it was impossible to reach the location. Many Japanese people – including school groups – were strolling around the area with their cameras.

The work will continue for years. It begs the question, though, what for? This is not the first time the Sanriku coast has been hit by a tsunami and it won’t be the last either.  This time the destruction and death toll were huge, mostly because of the coastal development and population concentrations on the waterfront. So why spend all the trillions of yen and years of civil works only so that the coast could be rebuilt and people could reestablish themselves in the hazard zone? Unfortunately, this seems to be an expression of the Japanese attitude, a downside of the tenacity: Engineering and civil works to tame the nature – and at the same time do irrevocable damage to the surrounding mountain environments. Here this seems even more futile because the coast has already been depopulated and virtually all people left for the cities and towns further inland, many with no intent on returning. Some of the old folks may want to return to their home areas but even they would likely not want to live right on the coast where their old neighborhoods were destroyed and friends died.  Most likely, the official approach will be to provide homogenous housing, which will be convenient but not appealing.

Naturally, Rikuzentakata is not the only community on the Sanriku coast that is struggling with recovery. The central government is paying for the efforts but it is the local governments that decide on how the money should be spent. In fact, the central government has been criticized for not spending enough of the allocated funds, so massive civil works like those here are welcome, so that large amounts of funds can be disbursed. The local governments have a wish to make the communities livable again. The trouble is that nobody knows who and how many people would eventually return.

The tsunami disaster had a profound impact on the coastal communities, not only in a physical sense. The very fabric of the communities was torn apart. As my friend, Prof. Mikiyasu Nakayama of Tokyo University, has found in his research, many younger people who used to live with the grandparents in three generation households – especially young women dominated by the mothers-in-law – have found it liberating to move away and establish a new life on their own in the urban areas. Even others have realized that modern life in the city with all its amenities is convenient. There is no going back.