Folly of quake predictions

In a recent report weighing responses to major Nankai Trough quakes, which will affect vast areas of the Pacific coast stretching from Shizuoka to Kyushu, a panel of experts from the government’s Central Disaster Management Council said it is difficult to predict the occurrence of an earthquake with a high degree of certainty. It thus called for a review of anti-disaster measures based on the assumption that quake forecasts are possible — an idea presumed by the Law On Special Measures Concerning Countermeasures for Large-Scale Earthquakes. The panel’s new position represents a step in the right direction because past experience, including the Great Hanshin Earthquake of 1995, the Great East Japan Earthquake of 2011 and the Kumamoto quakes of 2016, suggests that it is impossible to predict major quakes.

At the same time, the report called on the government to work out a system for advance evacuations in case such phenomena as crustal movements and foreshocks that can be linked to major quakes are detected. The government plans to launch a project to choose several model districts in areas that can be potentially hit by Nankai Trough quakes and study procedures for evacuations before the quakes hit.

The panel fell short of calling for abolishing the law on large-scale earthquakes, putting off a conclusion on the matter. What the government should do, however, is scrap the law and divert the funding, manpower and administrative energy spent on quake forecasts to beefing up disaster response measures to get people to be better prepared to cope with big quakes that can strike out of the blue.

Introduced in 1978, the law empowers the prime minister to issue an emergency alert that an earthquake is expected to soon strike the Tokai region around Shizuoka Prefecture on the basis of a short-term forecast. A six-member panel was set up in 1979 to evaluate precursors of the much-feared large-scale quake — whose hypocenter would be in a zone covering the central and western parts of the prefecture, Suruga Bay and the Sea of Enshu — by receiving data from strain meters installed hundreds of meters underground in 27 locations.

In issuing an alert, the prime minister can order such steps as evacuating local residents, halting train services, restricting road traffic and suspending bank operations. The problem is that the idea behind the law — that an imminent earthquake is predictable — has no scientific grounds.

The idea of advance evacuation of residents is not without problems, either. The report, for example, proposed announcing the probability of a large-scale quake hitting the western part of the Nankai Trough zone after a major temblor has taken place in the eastern part of the zone — on the basis of past records of multiple quakes hitting the areas at certain intervals. But given the current state of knowledge derived from past studies, one wonders whether it is possible for seismologists to collect sufficient data to call for an advanced evacuation. And even using the same data, seismologists’s evaluations on the chance of big quakes happening may differ.

In addition to calling for advance evacuation, the seismologists will be required to determine when to end the evacuation if the quake doesn’t strike. An extended evacuation could severely affect people’s lives and local economic activities. It must be emphasized that creating a system for advance evacuation would be only one of the measures that can be taken to mitigate the damage from big quakes. The government should return to the basics — taking every possible step to contain damage on the assumption that a large-scale quake can strike suddenly.

In a related move, a panel of experts at the Cabinet Office issued a separate report stating that in the event of a major quake directly hitting the Tokyo metropolitan area, up to nearly 1 million emergency housing units would be necessary to accommodate evacuees — but this can mostly be filled by the government renting private apartments in the area, and that a relatively low number of 80,000 prefabricated units would have to be constructed. In case of a Nankai Trough big quake, however, up to 840,000 such temporary units would need to be built, since an estimated 2.05 million housing units would be needed but private apartments would only cover 1.2 million. Securing emergency accommodations would be a major challenge in the event of a catastrophic Nankai Trough quake.

Municipal authorities should also be aware of the importance of urban and community development from a long-term viewpoint of reducing damage from disasters, such as relocation of residences or city centers from areas that could be devastated by tsunami. This kind of policy should go hand in hand with such measures as preparing for rapid evacuations and making individual buildings sufficiently quake-resistant.