Photo/Illutration Snow is piled up in Kushiro, Hokkaido, in January 2016. (Asahi Shimbun file photo)

Estimates prepared for the Cabinet project that if a massive magnitude-9 earthquake struck off the Pacific coast from Hokkaido to Tohoku, it would generate a tsunami and kill up to 199,000 people under the worst-case scenario.

While earthquakes that strong are rare, the Cabinet Office released the estimates on Dec. 21 as part of its disaster-prevention planning efforts.

That level of damage would far exceed the 2011 Great East Japan Earthquake and tsunami that killed more than 20,000 people.

But the Cabinet Office also said the damage could be reduced by 80 percent if disaster-prevention measures are taken.

The estimate was made for a magnitude-9.1 earthquake in the Japan Trench, which stretches from off Tohoku to off Hidaka in Hokkaido, and a magnitude-9.3 earthquake in the Chishima Trench, which runs from off Tokachi to the Kuril Islands in Hokkaido.

A panel of experts established by the Cabinet Office released an estimate in April 2020 for tsunami height and the size of the inundation zone that would be caused by the two possible quakes.

This time around, the panel crunched the numbers and summarized the estimated harm it would cause to humans and damage to physical infrastructure.

A megaquake in the Japan Trench would cause the most damage.

If it occurred at night in the dead of winter, it would take longer for people to escape due to the accumulated snow. The death toll would be as high as 199,000 across seven prefectures. Most of the deaths, about 70 percent, would be in Hokkaido, the estimate said.

In that hypothetical scenario, 220,000 buildings would have completely collapsed or burned down, and the economic damage would reach 31.3 trillion yen ($275.4 billion).

If a quake occurred in the Chishima Trench at night in the dead of winter, up to 100,000 people would die, the estimate said.

In both cases, almost all the deaths would be caused by tsunami.

“It is important to raise awareness about evacuation,” the Cabinet Office said.

It urges people to plan their evacuation routes in the event of a disaster, and to “consider evacuating by vehicle, depending on local circumstances.”

Winter is extremely cold in Hokkaido and Tohoku, and that would compound the situation further.

If people sought sanctuary from tsunami and remained outdoors for hours, it would put up to 42,000 people at risk of dying from hypothermia on top of the tsunami deaths.

But for both earthquakes, if people evacuate quickly, facilities such as tsunami evacuation towers are used and buildings are reinforced to be more resistant to earthquakes, the death toll could be reduced by 80 percent, the Cabinet Office said.

“Based on this damage estimate, not only governments but also companies, communities and individuals need to be prepared to respond to (a megaquake),” the report said.

In response to the 2011 disaster, the Central Disaster Prevention Council rolled out a prevention plan in 2014 for a megaquake and the mitigation of damages.

The plan urged people to prepare for earthquakes in the Japan and Chishima trenches, as well as in the event one occurs in the Nankai Trough or directly beneath the Tokyo metropolitan area.

The Cabinet Office has stated that a top-category earthquake is “extremely unlikely” given how infrequently they occur.

But it released the estimate for disaster-planning purposes and to consider worst-case scenarios. It also wants to raise public awareness of the importance of disaster prevention and planning.

(This article was written by Hidemasa Yoshizawa and Takaoki Yamamoto.)

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