Eastern Japan Faces Urgent Risk of Major Earthquake, Joint Study Warns

Regions where magnitude 9-class shaking is expected

A previously unseen large-scale disaster may be imminent off the coast of northern Japan in the waters near Hokkaido.

In February of this year, a joint research team from Tohoku University, Hokkaido University, and Japan Agency for Marine-Earth Science and Technology announced the possibility that a magnitude 9-class megaquake — comparable to the Great East Japan Earthquake — could be imminent along the Kuril Trench off the Pacific coast of Hokkaido. Assistant Professor Fumiaki Tomita of the International Research Institute of Disaster Science at Tohoku University, a member of the research team, explained:

“In the southwestern part of the Kuril Trench, it is believed — based on tsunami deposits — that giant earthquakes have repeatedly occurred at intervals of roughly 400 years. Although the exact year of the previous event is unknown, it is thought that around the 17th century, between 1611 and 1637, a magnitude 8.8 earthquake occurred, sending tsunami waves up to 20 meters high onto the Pacific coast of Hokkaido.

However, until now there had been no offshore seafloor observation network along the Kuril Trench, so we had no direct data.”

The research team installed observation points at three locations on the seafloor off the Pacific coast of Hokkaido. Over a five-year period starting in 2019, they directly measured crustal deformation using acoustic and other data. The results revealed alarming findings.

“At two points near the Kuril Trench — on the Pacific Plate and the North American Plate — we confirmed that the crust is moving west-northwest at about 8 centimeters per year. If strain has been accumulating since the last earthquake in the 17th century, the total displacement could reach 20.5 to 30 meters over roughly 400 years.

The 17th-century earthquake is believed to have occurred when the plate boundary slipped by about 25 meters. This suggests there is already an enormous amount of energy accumulated in the Kuril Trench capable of triggering a megaquake,” said Tomita.

Estimates also suggest hundreds of thousands of casualties

n December 2021, Japan’s Cabinet Office of Japan released damage projections for a potential megaquake occurring along the Kuril Trench. If such a quake were to strike in the middle of a winter night with heavy snowfall making evacuation difficult, the death toll could reach as high as 100,000, with approximately 84,000 buildings destroyed.

Hiroki Kamata, a specialist in earth sciences and emeritus professor at Kyoto University, explained:

“If a magnitude 9-class megaquake occurs along the Kuril Trench, intense shaking equivalent to seismic intensity 7 and tsunami waves approaching 30 meters in height could strike the Pacific coasts of Hokkaido Prefecture and Tohoku region. However, the risk of a giant earthquake is not limited to the Kuril Trench.

The Japan Trench off the Pacific coast of northeastern Japan — where the Pacific Plate subducts beneath the North American Plate — could also produce a massive earthquake at any time. A huge tsunami could inundate a wide area from Hokkaido to the Kanto region. According to the Cabinet Office, the death toll could reach up to 199,000 people, with as many as 220,000 buildings completely destroyed or burned down.”

The economic damage would also be enormous.

“Estimated losses are around 17 trillion yen for a Kuril Trench earthquake and about 31 trillion yen for a Japan Trench earthquake. Most of this damage would come from tsunami destruction along Pacific coastal areas, including buildings and port infrastructure. Roads and railways would be severed, and lifelines such as electricity, water, and gas would be cut off. Smartphones and computers could also lose connectivity for extended periods.

Both human and economic damage would far exceed the Great East Japan Earthquake, and Hokkaido and the Tohoku region would likely suffer catastrophic devastation,” Kamata said.

From “FRIDAY” (April 17–24, 2026 combined issue)

A follow-up article discusses the possibility of another major earthquake threatening the Tokyo metropolitan area as well.