Countermeasures against tsunami in Sea of Japan not to be taken lightly

August 28, 2014

Editorial: Step up efforts to take countermeasures against Sea of Japan tsunami

http://mainichi.jp/english/english/perspectives/news/20140828p2a00m0na001000c.html

A panel of experts set up by the Land, Infrastructure, Transport and Tourism Ministry has announced estimates on the height of tsunami generated by major earthquakes that could occur in faults below the Sea of Japan.

Up to 23-meter-high tsunami are expected to hit Setana, Hokkaido, while five- to 12-meter-high tsunami are estimated in areas along the eastern to northeastern Sea of Japan coast from Hokkaido to Fukui Prefecture. Some three- to four-meter-high tsunami could hit areas along the western Sea of Japan coast from Kyoto Prefecture to Kyushu.

Although experts do not think there is a seismic source in the Sea of Japan that could trigger a huge temblor, like the Nankai Trough in the Pacific Ocean south of the Japanese archipelago, earthquakes whose focal points are situated on the bottom of the Sea of Japan are estimated to cause higher tsunami despite their smaller seismic scales.

National and local governments are slow to work out countermeasures against Sea of Japan earthquakes as compared with responses to possible temblors in the Pacific Ocean. This is the first time that the national government has estimated the height of tsunami in each municipality along the Sea of Japan coast. By fully utilizing the estimates, the national government and local bodies concerned should take all possible measures to protect residents and their neighborhoods along the Sea of Japan coast from tsunami.

Massive tsunami that caused casualties have hit areas along the Sea of Japan coast in the past. The magnitude-7.7 central Sea of Japan earthquake in 1983 caused a tsunami that killed about 100 people, while a tsunami generated by a temblor with a magnitude of 7.8 in the southwest off Hokkaido in 1993 left 230 people dead or missing.

However, there are far fewer records of earthquakes in the Sea of Japan than those in the Pacific Ocean and little progress has been made on a geological survey on the seabed of the Sea of Japan. Legislation aimed at encouraging local bodies to step up countermeasures against tsunami, which came into effect following the March 2011 Great East Japan Earthquake and tsunami, requires prefectural governments to estimate the areas that are likely to be submerged by tsunami. However, prefectural governments have previously struggled to make estimates due to a lack of specific assessments of earthquake and tsunami on the Sea of Japan coast. As such, the panel of experts recently conducted analyses.

Based on data on past earthquakes and the crustal structure, the panel reportedly examined 60 underwater faults from Hokkaido to Nagasaki, assumed that these faults could trigger magnitude-6.8 to 7.9 temblors and then estimated the height of tsunami that could be generated by such quakes.

Experts say such relatively small earthquakes could trigger higher tsunami because these faults below the seabed of the Sea of Japan are relatively shallow. Since the faults are close to the archipelago, tsunami generated by earthquakes occurring in these faults could reach the archipelago in a short period of time. The panel estimates that tsunami waves could hit some areas within a minute after a quake, and that at least 30-centimeter-high waves, which could sweep away people, might hit 82 municipalities within 10 minutes.

Based on these estimates, prefectural and municipal governments in areas along the Sea of Japan coast are required to review their disaster-prevention plans. Top priority should be placed on safely evacuating local residents. A panel of experts within the government's Central Disaster Management Council recommended in September 2011 that all regions be rebuilt to make sure that residents can walk to safe locations within about five minutes after tsunami hit. The panel made the recommendation on the assumption that a huge earthquake could hit areas along the Pacific coast. However, similar countermeasures should be taken in areas along the Sea of Japan coast. Both national and local governments along the Sea of Japan coast should designate evacuation routes and regularly conduct evacuation drills in preparation for deadly tsunami, while implementing all possible measures to lessen damage caused by such disasters.

The panel also announced its estimates of the height of tsunami that could hit 11 nuclear power stations along the Sea of Japan coast, but the estimated figures were below those by the plant operators. Still, there is a possibility that the estimates could change as seismological research progresses. As such, it is only natural that authorities should strictly examine the safety of each nuclear plant.

August 28, 2014(Mainichi Japan)