A massive earthquake and tsunami could strike Japan's Hokkaido Pacific coast in the near future, according to new research suggesting conditions mirror those before a devastating 17th-century quake.
A joint research team from Tohoku University and Hokkaido University published findings in the international journal Communications Earth & Environment on the 14th, the Mainichi Shimbun reported on the 23rd (local time).
The high-risk zone is the Kuril Trench, where the Pacific Plate rapidly subducts beneath the Okhotsk Plate. This region has historically produced magnitude 8-9 earthquakes and tsunamis repeatedly.
Tohoku University researchers estimate mega-quakes have struck Hokkaido's Pacific coast at roughly 400-year intervals. The most recent major quake, estimated at magnitude 8.8, occurred between 1611 and 1637. The resulting tsunami reportedly flooded areas 1-4 kilometers inland from the coastline.
From 2019 to 2024, researchers from Tohoku University, Hokkaido University, and the Japan Agency for Marine-Earth Science and Technology installed three observation devices on the Nemuro seabed to measure crustal movements. Data showed both the Pacific Plate and continental plate near the trench are moving west-northwest at approximately 8 centimeters annually.
If crustal deformation has accumulated since the 17th-century quake, the Pacific Plate's cumulative displacement could reach 20.5-30 meters, researchers estimated. Given that the plate boundary appeared to shift about 25 meters during that event, sufficient energy for an equivalent earthquake may have already stored.
The Mainichi noted that a seismic gap was identified near the Japan Trench off Miyagi Prefecture's coast before the magnitude 9.0 Great East Japan Earthquake on March 11, 2011. Massive fault movement then triggered a catastrophic tsunami.
"Tsunamis reaching up to approximately 20 meters are expected along Hokkaido's coast," Tohoku University Assistant Professor Fumiaki Tomita told the Mainichi. "I urge residents to live with awareness that a mega-quake will inevitably occur in the future."
Aomori Prefecture, facing Hokkaido, experienced a magnitude 7.5 earthquake on December 9 last year. The Yomiuri Shimbun reported that Japan's government Earthquake Research Committee raised on the 14th the probability of a magnitude 7.8-8.5 earthquake occurring offshore Nemuro in eastern Hokkaido within 30 years from "approximately 80%" to "approximately 90%."
The committee cited that major earthquakes have struck offshore Nemuro at average intervals of 65 years, with more than 50 years having passed since the last major event.
The committee maintained two existing probability estimates for the Nankai Trough mega-quake: "60-90% or higher" and "20-50%." The Nankai mega-quake refers to magnitude 8-9 earthquakes occurring in the Nankai Trough, extending from offshore Shizuoka Prefecture to southern Shikoku and eastern Kyushu waters. Historically, major earthquakes have recurred in this region at 100-200 year intervals.