社説:南海トラフ津波 想定受け止め対策を

(Mainichi Japan) April 3, 2012
Editorial: Catastrophic quake, tsunami projections demand policy rethink
社説:南海トラフ津波 想定受け止め対策を

If a major earthquake hits the "Nankai Trough" off central and western Japan's Pacific coast, the resulting tsunami could tower two to three times higher than previously estimated, according to an expert government panel announcement on March 31.

The panel assumed a magnitude-9.1 temblor -- close to the same strength as the Great East Japan Earthquake of March last year -- and put together maximum damage estimates based on the latest scientific data.

The result: a quake measuring a high-6 on the Japanese 7-point intensity scale and destruction to 395 municipalities in 21 prefectures -- more than five times greater than was projected in a 2003 study. Moreover, if the quake hit at high-tide, the resulting tsunami would top 20 meters when they slammed into 23 municipalities in the Tokyo islands and Shizuoka, Aichi, Mie, Tokushima and Kochi prefectures. The largest projected wave, at 34.4 meters high, would hit the town of Kuroshio, Kochi Prefecture.

Of especially serious note in the estimates is the maximum 21-meter-high tsunami projected for Chubu Electric Power Co.'s Hamaoka nuclear power plant in Omaezaki, Shizuoka Prefecture. After the meltdowns at the Fukushima No. 1 nuclear plant -- triggered when backup generators powering the reactors' cooling systems were flooded by tsunami -- Chubu Electric began building an 18-meter-tall, 1.6-kilometer-long tsunami breakwater to guard the Hamaoka plant.

The projected tsunami, however, would get over the barrier and swamp the station. Obviously, Chubu Electric's tsunami countermeasures need a drastic rethink.

Then there are the tsunami estimates for major urban centers. A wave over 20 meters high is projected for Toyohashi, Aichi Prefecture, and waves over 10 meters for the cities of Shizuoka, Hamamatsu, Kochi and Miyazaki.

Starting this month, the expert panel will begin releasing flood projections based on the estimated tsunami heights. Meanwhile, the Cabinet Office's Central Disaster Prevention Council is scheduled to announce total damage projections, including the number of dead and total buildings destroyed, in June this year.

The foundation of any anti-tsunami damage policy must be the lessons learned from the experience of last year's terrible waves, which took the lives of many who could not flee in time. Municipalities along Japan's Pacific coast, menaced by three projected catastrophic quakes -- Tokai, Tonankai and Nankai -- along the Nankai Trough, must formulate such policies especially quickly.

An expert investigative committee under the disaster prevention council concluded last year that communities should be built such that anyone could walk to safety within about five minutes in case of a tsunami. However, the latest estimates warn of one-meter tsunami hitting the coast in about 2 minutes after a major quake. There are some local governments that have taken concrete tsunami safety measures, such as designating tall buildings as evacuation sites, building evacuation towers and demarking evacuation routes to high ground. In light of the new estimates, however, a re-evaluation of these measures -- including minimum evacuation times -- is required.

Finally, the state's financial support cannot be ignored. The government is set to draw up measures to deal with current difficulties this summer. What's essential, however, is that the central, prefectural and municipal governments build a unified policy on this issue. We call for deep discussion on what should be given priority in building such policy.

Furthermore, the countermeasures laid out in the special measures law for the projected Tokai earthquake are different than those for Tonankai or Nankai quakes. Prefectural governors and other people in the areas likely to be affected, however, have begun calling for a united countermeasures law. If changes in the law are required, then the central government should get working on them as soon as possible.

毎日新聞 2012年4月3日 東京朝刊

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