TOKYO — It sounds like a weather forecast — not for today, but for the next 30 years.
There is a 70 percent chance of a 7.2-magnitude earthquake between now and 2040 in the southern Kanto area around Tokyo, and a 90 percent chance in nearby Ibaraki, according to Japan's Earthquake Research Promotion agency. The likelihood of 8.0-magnitude quakes is 87 percent in the Tokai region about 100 miles southwest of Tokyo, 70 percent in Tonankai near the automotive capital of Nagoya, and 60 percent for a massive 8.4-magnitude Nankai quake near the sprawling Osaka area in western Japan.
Three months after the March 11 9.0-magnitude earthquake and tsunami, which killed at least 25,000 people, Japanese leaders and citizens are taking earthquake forecasts seriously and reviewing preparations for disasters. A 6.7-magnitude quake off northeastern Japan last week sent many tsunami survivors heading once again for high ground. It reminded people that Japan's spell of disasters might not be over. "The short answer is: nobody knows when the next one will strike," said Satoko Oki, a seismologist at the University of Tokyo. "So we have to be prepared." Many in Japan fear a repeat of what happened to Indonesia after a 9.0-magnitude quake off Sumatra on Dec. 26, 2004, triggered a tsunami that killed more than 200,000 across the Indian Ocean. Three months later, on March 28, 2005, an 8.7-magnitude quake — one of the strongest ever recorded – struck Indonesia along the same fault line, killing more than a thousand people in toppled buildings and falling debris.
"Seismologists regret that we thought such a massive tsunami was beyond imagination," said Ms. Oki, who recently measured a tsunami wave 120 feet high in a narrow cove in northeastern Japan. "We should have looked at what happened in 2004 in the Indian Ocean and accepted that it could happen in Japan as well."
Historians figure that at least 195 tsunamis have hit Japan since 400 AD, including three recent killers: off Akita province in 1983; Okushiri near Hokkaido in 1993; and the March 11 tsunami in the northeastern region known in Japanese as Tohoku. Because of that history, Japan has perhaps more detailed information online about past and potential disasters than any other nation. The Earthquake Research Promotion office's website features detailed maps and charts about the probability of major quakes in various areas. The Metropolitan Tokyo Police Department's website offers earthquake and tsunami precautions in Japanese, English and Chinese.
When quakes strike, TV networks immediately broadcast information about the strength, depth and location of the temblors. Many coastal dwellers go to the Japan Meteorological Agency's website, which has a simple map showing tsunami warnings. Though high-rise office buildings swayed like grass in the breeze, and many homes shook violently for more than three minutes, Tokyo escaped heavy damage from the March 11 quake, the largest ever recorded in Japan. "We're prone to disasters more than other cities, so we have to be prepared better than other cities," said Yuichi Kogasaki, director in charge of the Tokyo Metropolitan Government's disaster prevention division. "Researchers are now investigating what could happen here. 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 5,600 to 7,800 people, injure 160,000 and trap 22,000. It would damage about 500,000 buildings, spark at least 300,000 fires and force 4 million people to evacuate. Mr. Kogasaki said those numbers likely will be revised upward. Many scientists believe the Kanto plain, home to 35 million people and a third of Japan's economy, is exposed to the Sagami and Nankai troughs, which spawned tsunamis hitting Kanto in 1677, 1703, 1854, 1855, 1894, 1923, 1944 and 1946.
In 1703, the 8.2-magnitude Genroku quake and tsunami in Sagami Bay and the Boso peninsula flanking Tokyo killed at least 6,500 people. In 1923, a 7.9-magnitude quake and fire killed more than 140,000 across Tokyo and Yokohama. The tsunami – with 39-foot waves in Atami and 30-foot waves on the Chiba coast – drowned people on the Enoshima causeway and Yuigahama beach. It destroyed the base of the Giant Buddha in Kamakura, which also was hit by a tsunami in 1498.
Ms. Oki said that many seismologists now believe that anything is possible — even an eruption of Mount Fuji, the picturesque, snow-capped volcano and Japan's highest mountain. But she said there is a "really low possibility" of a tsunami devastating Tokyo because the narrow mouth of Tokyo Bay tends to deflect such tidal waves. The bay also has a shallow, flat bottom and slopes that funnel water to the surrounding area. "The slope is really lucky for us in Tokyo," Ms. Oki said. "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 … and we would have time to escape."
She is more worried about landslides, fires and train accidents — and Japan's tendency to forget its history. "Many people in Tohoku died because they didn't know history, and they didn't imagine a [30-foot-high] wave would attack them," she said. "Tsunamis are scary, and I'm scared of them, too. But being ignorant is the scariest thing."