The national government's Earthquake Research Committee has released a long-term assessment predicting that there is as much as a 40 percent chance that a magnitude-9 earthquake, almost the same power as the March 2011 Great East Japan Earthquake, could strike along the Kuril Trench off Hokkaido within 30 years.
The public should keep in mind that a massive temblor could occur at any time. The central government and local bodies concerned need to beef up their countermeasures against such a possible earthquake.
The government has urged the public to be on the alert against a possible magnitude-9 earthquake along the Nankai Trough off central and western Japan as there is as much as a 70 percent chance of such a quake hitting within three decades. The latest assessment by the Earthquake Research Committee shows that there is no place on the Pacific Ocean side of the Japanese archipelago that is immune from such a huge quake.
Throughout history, massive earthquakes have repeatedly struck along the Kuril Trench, where the Pacific plate sinks below the North American plate. The Earthquake Research Committee has predicted that a magnitude-9 temblor could hit in three areas -- off Tokachi, off Nemuro and off Shikotan to the Etorofu islands that are part of the Russian-held, Japan-claimed Northern Territories.
The panel assumes that an earthquake triggering a massive tsunami has occurred in these areas every 340 to 380 years on average with the latest one having struck about 400 years ago. There are reportedly traces of tsunami waves triggered by the quake hitting inland areas up to 4 kilometers from the coast.
Previously, the government had not assumed that earthquakes could simultaneously hit in these three areas. The committee's assessment that multiple huge quakes could strike is appropriate.
In 2012, the Hokkaido Prefectural Government released its prediction of floods caused by tsunami waves on the assumption that the northernmost prefecture will be hit by a magnitude-9.1 earthquake. In the meantime, the national government's Central Disaster Prevention Council is working out its prediction of casualties and other damage from such a huge temblor. The council should speed up its work on this matter.
The Hokkaido Prefectural Government's simulation predicts that the first tsunami waves would reach the prefecture's coastal areas about 20 minutes after a huge temblor. Since it is impossible to rely solely on coastal levees and other facilities for preventing damage from tsunami, countermeasures such as preparations for the swift evacuation of residents are indispensable.
Japan and Russia should cooperate in scientific research on earthquakes since it is imperative to conduct detailed research on deposited materials in the Northern Territories caused by past tsunamis to make even more reliable predictions of earthquakes.
The Earthquake Research Committee has not ruled out that a huge temblor's focal region could spread to an area off Aomori Prefecture, raising concerns that such a quake could hit nuclear complexes on the Shimokita Peninsula in the prefecture, which include nuclear plants and a spent nuclear fuel reprocessing plant.
The government and power companies should take necessary measures on the assumption that massive quakes could occur off coastlines from Hokkaido to Aomori Prefecture simultaneously.