Photo/Illutration A sign warns of tsunami at Aomori train station in Aomori Prefecture. A tsunami of up to 5 meters is expected to strike areas around the station in the event of a megaquake in the Japan Trench. (Toru Furusho)

The government was urged to amend a special law enacted in 2004 to prepare the public for a megaquake in either the Japan Trench that is part of the Pacific Rim of Fire off northeastern Japan or the Chishima trench that lies off Tokachi in Hokkaido and stretches to the Kuril Islands.

A working group within the Central Disaster Prevention Council on March 22 released a report on disaster-preparedness measures that should be taken in such an eventuality.

The council, which was established within the Cabinet Office, is made up of Cabinet members as well as the prime minister, representatives of public bodies and experts in the field. Its role is to draft basic disaster preparedness measures and discuss related issues.

In December 2021, the Cabinet Office released estimates of fatalities from a megaquake in the Japan Trench or the Chishima Trench.

Both trenches make up part of the seabed of the Pacific Ocean.

The Cabinet Office projected up to 199,000 fatalities in the event of a magnitude-9.1 megaquake in the Japan Trench late at night in winter and said that around 22,000 people could be injured. It estimated that 220,000 buildings could collapse or burn down, causing 31.3 trillion yen ($260 billion) in economic damage.

It also projected up to 100,000 deaths if a megaquake of 9.3 magnitude hits the Chishima Trench.

The council noted that towering tsunami pummel Pacific coastal areas from Hokkaido to Iwate Prefecture every 300 to 400 years. The last time a related tsunami of devastating power hit was in the 1600s, suggesting the possibility of another one happening soon.

The report said that if an earthquake of 7.0 magnitude or more hit the possible hypocenter of a megaquake that could strike either of the trenches or an area close by, the Japan Meteorological Agency should immediately inform the public of the risk of another massive earthquake of around magnitide-9.0 coming soon afterward. It called on the agency to reinforce warnings about earthquake preparedness.

Just two days prior to the magnitude-9.0 Great East Japan Earthquake in 2011, a magnitude-7.3 temblor occurred off the Sanriku coast, which is near the possible hypocenter of a megaquake that could strike the Japan Trench. The report also noted that 18 hours after a magnitude-7.0 earthquake hit off Etorofu island in the Kuril Islands in 1963, another quake of 8.5 magnitude struck.

Although an earthquake of 8.0 magnitude or more following a quake of around 7.0 magnitude occurs once in roughly 100 cases, the council said vigilance in preparedness against successive quakes could help save many lives.

The report also said that measures to prepare for devastating tsunami should take into account the probability of a megaquake occurring when temperatures are frigid.

It proposed constructing tsunami evacuation towers or roofed evacuation corridors in areas that could be affected by a megaquake so as to prevent accumulated snow from jeopardizing evacuation routes. It also suggested that low-lying less populated areas could provide safe evacuation routes if people are able to drive.

The Cabinet Office’s December estimate said that even if people found sanctuary from tsunami, a megaquake could put as many as 42,000 people at risk of dying from hypothermia. To prevent this, the working group’s report said shelters for evacuees need to stock heaters, cold protection clothing or goods, dry clothes, and self-heating emergency meals.

The working group also called for legislative measures and funding to prop up disaster-preparation measures.

Under a special law to prepare for a megaquake along the Nankai Trough off the Pacific coast, the government pays two-thirds of the cost incurred to build evacuation towers and other structures.

If the 2004 special law is amended, it will designate areas where measures to prepare for an earthquake and tsunami should be taken, and local authorities in those areas will be required to make plans to reduce the risk of people coming to harm when a natural disaster strikes.

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The Asahi Shimbun

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