Will a monster tsunami hit Tokyo soon?
The worst-case scenario is horrifying. Waves swamp Haneda airport and hurl freighters into Shinagawa office towers. Kawasaki chemical factories explode into toxic fires. Walls of water moving at jet speed pulverize, mangle or gut buildings and rise up to the fourth floor of the Japan Times in Shibaura.
The tsunami rushes up the Edo, Arakawa, Sumida, Tama and Meguro rivers, past Naka-meguro and into the bowl of Shibuya. The reclaimed lands of Ota, Minato, Chuo and especially Koto wards — already below sea level in places — become an uninhabitable swamp, setting the economy back decades.
As unbelievable as it seems, that’s the Tokyo equivalent of what happened to Rikuzen-takata, Kesennuma, Minami-Sanriku, Ishinomaki and about 50 areas along a 500-kilometer swathe of Japan on March 11.
In those areas, indented coastlines — which closely resemble Tokyo Bay from the air — pushed tsunamis up 10 meters higher than in other areas.
But could it happen here, in the world’s biggest city?
“Researchers are now investigating what could happen here,” says Yuichi Kogasaki, director in charge of the Tokyo Metropolitan Government’s disaster prevention division.
“Until recently, we never expected that such a big tsunami could happen in Tokyo. But now we realize the need to review all our master plans.”
The city’s previous study in 2006 estimated a 7.3 quake in “north Tokyo Bay” could kill between 5,600 and 7,800 people, injure 160,000, trap 22,000, damage about 500,000 buildings, spark at least 300,000 fires and force 4 million people to evacuate.
Even the March 11 quake, though far from Tokyo, caused liquefaction in Urayasu, set fire to fuel drums in Odaiba and Chiba and disrupted the supply chain.
“We’re prone to disasters more than other cities, so we have to be prepared better than other cities,” says Kogasaki.
Most officials and experts admit that Japan was prepared for an earthquake, not a tsunami. But calling the disasters “unimaginable” or “a thousand-year event,” as many did, ignores geological history and Japan’s connection to the Pacific Ring of Fire, where an 8.8 magnitude quake hit Chile last year, and a 9.1 off Indonesia killed 230,000 in the 2004 tsunami.
Not the first time
Though modern study of earthquakes only began in 1884, historians figure that at least 195 tsunamis have hit Japan since 400 AD, including three recent killers — off Akita in 1983, Okushiri near Hokkaido in 1993 and this winter in Tohoku. Tsunamis devastated roughly the same areas of Tohoku in 1896 and 1933 and many times before as well.
For Tokyo, it’s not a matter of if, but when. Japan’s Earthquake Research Promotion agency says the chances over the next 30 years of a 7.2 quake are 90 percent off Ibaraki and 70 percent in southern Kanto.
A quake that size in 1995 killed more than 6,000 people and flattened nearly every wooden structure in Kobe, a much less crowded city.
Moreover, the likelihood of 8.0 quakes are 87 percent in Tokai (the Shizuoka area), 70 percent in Tonankai (near Nagoya and Ise), and 60 percent for a massive 8.4 magnitude Nankai quake near Shikoku and Kansai.
Seismologists, who recognize the imperfect and developing nature of their science, believe the Kanto plain, home to 35 million people and a third of Japan’s economy, is exposed to the Sagami and Nankai troughs, where quakes have spawned tsunamis hitting Kanto in 1677, 1703, 1854, 1855, 1894, 1923, 1944 and 1946.
On New Year’s Eve in 1703, the 8.2 Genroku quake and tsunami in Sagami Bay and the Boso peninsula flanking Tokyo killed at least 6,500 people and created five-meter high seaside terraces in southern Chiba.
More famously, the 7.9 quake on September 1, 1923 killed more than 140,000, as gusts from a typhoon further north spread cooking fires across Yokohama and Tokyo. The tsunami — 12 meters high in Atami and nine in Aihama, Chiba — drowned people on the Enoshima causeway and Yuigahama beach and destroyed the base of the Giant Buddha in Kamakura, whihc was also hit by a 1498 tsunami.
Much of Tokyo sank by up to 50 centimeters, but tsunami damage is unclear, due to the fire damage. Photos of Kamakura and Asakusa then resemble Kesennuma now.
Though frightening, this historical reality also buttresses Japan’s faith in its extraordinary ability to recover.
Tokyo's tsunami history is unclear. Most past disasters hit Tokyo when people lived on higher ground and the ocean extended up to the Imperial Palace, before land reclamation projects formed most of Odaiba and the port area.
Prepare for the worst
The March 11 tsunami reminded Tokyo University seismologist Satoko Oki that it's best to be ready for anything — even an eruption of Mount Fuji.
In the Taro district of Miyako city in Iwate, she measured where the tsunami ran up a slope 38 meters above sea level; the water was 30 meters high in the port area, meaning over the head of anyone on a ninth-floor balcony.
But even a one-meter high tsunami can destroy wooden houses, she says, and a 50-centimeter surge can kill. “It’s like trying to stand in a fast-moving ocean up to your knees. You can’t do it.”
But she says there’s a “really low possibility” of a tsunami devastating Tokyo.
For example, the 8.4 Nankai quake and tsunami in 1854 wiped out houses in Shimoda, Uraga and Yokosuka, but not Tokyo proper, as the narrow mouth of Tokyo Bay tends to deflect tsunamis.
She says the bay has a shallow, flat bottom without the height differentials and slopes that funneled water to extreme levels in Tohoku.
Tokyo in the clear?
“The slope is really lucky for us in Tokyo,” she says. “A tsunami wouldn’t grow in a flat ocean bay. It wouldn’t be an attacking tsunami moving up a river. It would be a gradual series of waves, perhaps two meters high at most, and we would have time to escape.”
She’s more worried about landslides, fires and train accidents than tsunamis. Instead of building prison-like tsunami walls, she says it’s better to bolster houses built before 1981 against quakes and teach everyone — especially elementary school kids — about tsunamis.
“Many people in Tohoku died because they didn’t know their history and they didn’t imagine a 10-meter high wave would attack them,” she says.
“Tsunamis are scary, and I’m afraid of them too. But being ignorant is the scariest thing of all.”
If you feel a quake, trust you instincts and move away from the sea or rivers. Tokyo police say don’t wait for warnings — flee immediately to high ground.
Perhaps more than any other country, Japan has detailed information online (in English too) about past and potential disasters. Everyone should check out the Earthquake Research Promotion’s excellent map detailing the probability of major quakes in various areas.
The Japan Meteorological Agency has a simple map showing tsunami warnings.
Tokyo Metro Government’s site provides detailed information about earthquakes, but little about tsunamis other than hazards on islands such as the Izu and Ogasawara groups
Lastly, Tokyo police have posted a colorful, easy-to-read set of earthquake and tsunami precautions as a PDF in English that's available to download from their website.
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