A government panel is warning of a “high possibility” that an earthquake the size of the 2011 Great East Japan Earthquake will strike the area south of Hokkaido within the next 30 years.

The Headquarters for Earthquake Research Promotion, announcing the first revision in 13 years of quake predictions along the Chishima trench, said Dec. 19 that heightened disaster preparations should be made because the area appears long overdue for a gigantic quake.

The panel said the possibility was between 7 and 40 percent of an earthquake with a magnitude exceeding 8.8 occurring in an offshore focus area extending from Tokachi in south-central Hokkaido to Etorofu, one of the four islands making up the disputed Northern Territories.

The panel said quakes of that scale have stricken the area at average intervals of 340 to 380 years, with the most recent one believed to have hit about 400 years ago. Panel members said the end of the average cycle had already been exceeded.

The March 2011 earthquake in the Tohoku region registered a magnitude of 9.0. The quake and ensuing tsunami wiped out communities on the northeastern coast of Honshu island, leaving nearly 20,000 people dead or missing.

“I hope disaster preparations are reviewed based on the possibility that a super-gigantic quake like the one that struck the Tohoku region could also strike Hokkaido,” said Naoshi Hirata, a seismology professor at the University of Tokyo and chairman of the panel’s Earthquake Research Committee.

The panel for the first time calculated the possibility of a quake similar in scale to the 2011 quake striking Japan’s northernmost main island.

The Cabinet Office next year is expected to release new damage projections for such a quake off Hokkaido.

In 2006, the Central Disaster Management Council estimated that about 700 people in Hokkaido and 200 in Honshu would be killed by tsunami triggered by a Hokkaido quake.

The Headquarters for Earthquake Research Promotion on Dec. 19 also issued possibilities for gigantic earthquakes within more limited areas along the Chishima trench.

For example, there was about a 70-percent possibility of an earthquake with a magnitude between 7.8 and 8.5 striking offshore from Nemuro, while the possibility was 7 percent for an earthquake with a magnitude between 8 and 8.6 hitting offshore from the Tokachi region.


Much attention has focused on the possibility of a gigantic quake striking along the Nankai Trough and devastating large parts of western Japan, a region much more densely populated than Hokkaido.

But the panel’s announcement underscores that a much wider area of Japan is at risk of a killer quake.

Researchers have uncovered details about damage caused by past tsunami in eastern Hokkaido, but such discoveries have only been made in the past few decades.

Studies into past quake damage have made clear that gigantic quakes have rocked Hokkaido 18 times over the past 6,500 years.

The Headquarters for Earthquake Research Promotion used strong language about the high possibility of a super-gigantic earthquake because the average cycle for such quakes ended long ago.

It is unclear how large such a quake would be, considering the panel’s conclusions were based on limited historical documents and data from the Northern Territories.

And because the cycles of earthquakes are highly variable, much more time could pass before a gigantic earthquake does strike off Hokkaido.

However, the panel’s view was based on the painful lessons from the Great East Japan Earthquake, in which research results were not completely reflected in disaster management plans.

In addition, earthquakes of smaller magnitudes than those listed in the panel’s announcement can still generate devastating tsunami.

The public should recognize that the entire Pacific coast of eastern Japan, including Hokkaido, is an area where earthquakes and accompanying tsunami have often occurred in the past.

(This article was compiled from reports by Takahiro Takenouchi and Eisuke Sasaki, a senior staff writer.)