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The possibility of a powerful earthquake occurring over the next 30 years remains high on the Pacific side of Japan, the government has said.

The 2020 seismic hazard map, released Friday by the government’s Earthquake Research Committee, showed the probabilities of a quake measuring at least a lower 6, the third-highest level on the Japanese seismic intensity scale of 7.

The new map shows probabilities of at least 26% in the eastern part of Hokkaido, as well as the Pacific side of the Kanto region, Tokai region and Kinki and Shikoku regions.

Naoshi Hirata, chairman of the government's Earthquake Research Committee, speaks at a news conference ahead of the release of the 2020 seismic hazard map on March 19 at the Ministry of Education, Culture, Sports, Science and Technology in Tokyo. | KYODO
Naoshi Hirata, chairman of the government’s Earthquake Research Committee, speaks at a news conference ahead of the release of the 2020 seismic hazard map on March 19 at the Ministry of Education, Culture, Sports, Science and Technology in Tokyo. | KYODO

The results stem from high probabilities of two huge offshore quakes over the next 30 years.

One is a temblor with a magnitude of around 8 forecast to occur with an 80% probability along the Chishima Trench off Nemuro, Hokkaido.

The other one, seen occurring along the Nankai Trough off the country’s central to southwestern coast with a magnitude of 8 to 9, has a probability of 70% to 80%.

Many points on the map where the offices of prefectural capital cities and Hokkaido subprefectural bureaus are located showed slight increases in quake probabilities.

Of them, Mito, Ibaraki Prefecture, showed the highest probability at 81%, unchanged from the previous map released in 2018.

The probabilities stood at 80% in Nemuro, up from 78%, unchanged at 75% in Kochi and 75% in Tokushima, up from 73 %.

As recent geographical, geological and drilling survey data are reflected in the map, the probabilities dropped to 62% from 85% in Chiba and to 30% from 55% in Osaka.

The figured edged down to 47% from 48% in Tokyo.

The release of the 2020 map was delayed into 2021 as evaluations of quake probabilities along the Japan Trench and the Nankai Trough were updated.

The Tohoku region still sees aftershocks of the March 11, 2011, 9.0 magnitude Great East Japan Earthquake, which unleashed a deadly tsunami along the region’s Pacific coast.

Partly because of this, the probabilities of major quakes measuring at least a lower 6 over the coming 30 years remain high at 26% or higher along the Pacific coast of Miyagi and Fukushima prefectures.

Shizuoka and Yamanashi prefectures as well as the eastern part of Nagano Prefecture, showed lower probabilities because of updated quake evaluations, although they are still at high levels.

“We want people to check the areas of their homes, schools and workplaces on the map and take steps such as quake-proofing furniture,” said Naoshi Hirata, chairman of the committee.

The Japanese version of the map is accessible at the website of the government’s Headquarters for Earthquake Research Promotion.

Visitors to the site can pick a location and see the quake probability as well as how prone it is to shake on the National Research Institute for Earth Science and Disaster Resilience’s J-SHIS online hazard map.

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