Coping with a Nankai megaquake

Apanel of the Cabinet Office’s Central Disaster Prevention Council on March 18 predicted that if a megaquake of magnitude-9.1 occurs in the Nankai Trough off the Pacific coasts, the quake and its ensuing tsunami will cause economic damage amounting to some ¥220 trillion, more than 40 percent of Japan’s gross domestic product.

The central and local governments should promptly work out programs aimed at reducing the predicted damage and accelerating postdisaster reconstruction. The panel did not mention damage estimates for nuclear power plants for technical reasons.

An August 2012 estimate showed that a megaquake of magnitude-9 in the Nankai Trough, a 900-km subduction zone off the Pacific coasts stretching from Shizuoka Prefecture to Shikoku, could kill up to 323,000 people in 30 prefectures including Tokyo, with about 70 percent of the deaths tsunami-related.

Malfunctioning water gates would cause 23,000 more deaths. The probability of a magnitude-9 megaquake is once in 1,000 years or less. But a magnitude-8 quake happens once in 100 to 150 years in the Nankai Trough. The latest such quake occurred off Kii Peninsula on Dec. 7, 1944. The probability is high that such a quake will occur within a few dozen years.

The panel said that the magnitude-9.1 quake and its subsequent tsunami will inflict immediate damage of ¥169.5 trillion, about 10 times the ¥17 trillion damage caused by the 3/11 disasters, to assets such as buildings, lifelines and infrastructure in Tokyo and 39 prefectures lying west of Tokyo. Reduction in production activities and services will cause economic damage of ¥44.7 trillion over a period of one year. Damage over a half-year period from destruction of railways and roads will reach ¥6.1 trillion.

Parties concerned must push the work of making buildings quake-proof. The panel thinks that if all the buildings are so renovated, damage to assets by such a strong quake will be cut by 50 percent and damage to economic activities, by nearly 30 percent.

Businesses need to write plans on how to continue economic activities if hit by a massive disaster. The central and local governments must work out schedules for the implementation of preemptive projects aimed at minimizing damage as well as for post-disaster reconstruction, and plan how to fund them.

The panel predicted that some 9.5 million people will have to evacuate. Many people will not be able to go home and many communities will be isolated as outside assistance may not come quickly. It is important for communities to strengthen their ability to cope with severe disasters. Local governments, schools, businesses and households also need to store a week’s worth of food and water rather than three days as currently recommended.

A megadisaster will also likely knock out power sources, therefore the public and private sectors should accelerate the diversification of energy sources, including the installment of private power generators. Households should stock up on butane gas canisters for cooking and battery-powered lights.

  • phu

    The lasting legacy of the Tohoku earthquake appears to be that Japan will be, at least for the foreseeable future, totally and ineffectually obsessed with predicting unpredictable natural disasters. All the “planning” (i.e. vague suggestions no one has the time or money to implement) in the world will not help in the event any of these things actually happens. In the meantime, this waste of time, money, and public anxiety will continue to do more harm than good. Thanks a lot, fearmongers. This is exactly what the Japanese people do NOT need.

  • nosnurbd

    This is information which needs to be considered. True, earthquakes are not predictable, but they cannot be ignored either. Even National Geographic got into the “fearmongering” about the Nankai Trough in its October 1990 issue, well before the 3/11 event. Earthquakes are a part of life in Japan and so should be preparation and planning for the inevitable!