An experts’ panel at the Central Disaster Management Council of the Cabinet Office on June 26 announced in its interim report a new approach in working out countermeasures to large-scale earthquakes and tsunami. It took lessons from the March 11 quake and tsunami, which devastated the Tohoku Pacific coastal areas, killing some 15,500 people with some 7,200 more people missing.
The central point in the report is the emphasis on the importance of “software” in preparations for major quakes and tsunami — the same direction as taken by the Restoration Design Council.
The disaster management council is headed by the prime minister and includes all the Cabinet ministers, heads of public organizations like the Japan Red Cross and experts.
The central government must flesh out the software side of disaster prevention and show local governments as quickly as possible what concrete measures they must take.
The panel pointed out that damage from the March 11 disasters was catastrophic because the central and local governments pushed anti-disaster measures without taking into consideration the possibility that an earthquake and tsunami of the scales of the March 11 disasters could occur.
In the past, the forecast of large-scale earthquakes was based on records spanning several hundred years. Countermeasures were based on the assumption that major earthquakes that had happened frequently during the span had a high probability of recurring, the panel said.
But during the time span of several hundred years, a quake of the scale of the one that hit on March 11 did not happen.
The panel said that the time span to be studied for prediction of a large-scale earthquake should be extended back 1,000 years or so. It is said that a major quake that happened in 869 during the Jogan Era of the Heian Period was close to the March quake in power. The Jogan quake is believed to have caused tsunami that hit present-day Miyagi and Fukushima prefectures.
The panel said that the central government and experts concerned must do some soul-searching over why they excluded the effects of the Jogan earthquake during their studies of past quakes. It also stressed the need to study not only written records but also littoral sediment layers to estimate the force of past tsunami.
Mr. Yoshiaki Kawata, head of the panel and former head of the Research Center for Disaster Reduction Systems of Kyoto University’s Disaster Prevention Research Institute, said there is the need to “push comprehensive measures” to deal with not only a quake likely to happen once every 50 to 100 years but also a much stronger one likely to happen once in 1,000 years.
But the panel thinks that it is unrealistic in terms of cost to build sea walls that can stop once-in-1,000-years mega-tsunami. Still, it said that sea walls to cope with less powerful once-in-50-to-100-years tsunami must be built.
The panel said that while these sea walls might not hold back a once-in-a-millennium mega-tsunami, they would at least delay its arrival at inland locations.
This thinking is based on the assumption that such sea walls would be strong enough to withstand the force of a tsunami that occurs once in a millennium. New sea wall design will become necessary.
Under this thinking, it will be important to establish a system that will enable people to flee to safe places once a tsunami is forecast. It will require improving evacuation routes, building evacuation towers and preventing construction of buildings in areas where damage from tsunami is expected to be great.
Very strong quakes are predicted to occur off Shizuoka Prefecture and in western areas in the first half of this century. These quakes are already named the Tokai, Tonankai and Nankai earthquakes. One quake occurring could trigger the other two.
The central government and local governments concerned need to step up preparations for these quakes by taking into consideration the panel’s thinking.
In the case of the March 11 earthquake and tsunami, the Meteorological Agency issued a tsunami warning several minutes after the quake happened. But many people died because they did not know in what direction they should flee or because there was difficulty in leading children and elderly people to safety.
The central and local governments need to carefully study topographical features in areas likely to be hit by tsunami, draw hazard maps showing where tsunami water is most likely to intrude, and prepare escape routes.
They also need to improve evacuation training for local residents and disaster prevention or reduction education for children. They have to think about the possibility that past training and education may have been perfunctory.
The height of tsunami forecast in the first warning March 11 was lower than the actual height. Some people complained that because the warning predicted that the tsunami would be three meters high, they thought they did not have to escape.
Both the central and local governments must closely examine what went wrong with the warnings and evacuations on March 11. The lessons should be applied so that correct information will be given promptly to help people, both young and old, evacuate in time ahead of a future disaster.
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