Japan’s government has put out stark numbers: up to 199,000 people could die if a massive earthquake triggers a major tsunami along the Japan and Chishima trenches.
The warning follows a magnitude 7.5 earthquake that hit off Aomori Prefecture’s eastern coast on 8 December 2025. It registered an upper six on Japan’s seismic intensity scale.
For the first time since the system started in 2022, the Japan Meteorological Agency (JMA) issued a “subsequent earthquake advisory” after the 8 December quake. The agency noted that the chances of a megaquake in the same region had increased.
The advisory covers 182 municipalities across seven prefectures. Residents should stay alert, prepare for possible evacuation, and review safety measures while going about their daily routines.
JMA pointed out that globally, after a magnitude-seven or greater earthquake, a magnitude-eight or above event follows “in roughly one out of every 100 cases.”
A megaquake in the area could send tsunamis crashing into Japan’s Pacific coastline from Hokkaido down to Chiba Prefecture. The Pacific Plate beneath Japan forms two trenches—the Japan Trench and Chishima Trench. Both have caused many significant earthquakes over the years.
According to the Central Disaster Management Council, maximum-class tsunamis have struck along the trenches at intervals of about 300 to 400 years. The most recent one is thought to have happened in the 17th century. Experts believe a maximum-class earthquake and tsunami are coming soon.
The council’s 2021 damage projection estimated that a magnitude-nine earthquake along the Japan Trench, with tsunamis hitting the Pacific Coast from Hokkaido to Chiba on a winter night, could kill 199,000 people. Heavy snow during winter could block evacuations, pushing the death toll higher.
A similar event along the Chishima Trench could kill 100,000 people.
Even among those who manage to evacuate, an estimated 42,000 face higher death risk from hypothermia after a Japan Trench quake and 22,000 after a Chishima Trench quake.
The council said fatalities could drop by 80 per cent if people can reach higher ground quickly through better tsunami evacuation awareness. The risk of hypothermia could be wiped out by preparing cold-weather gear and heating equipment.
Professor Masahiro Nemoto of the Japanese Red Cross Hokkaido College of Nursing, a specialist in cold region disaster prevention, urged residents to prepare waterproof and cold-resistant outerwear, winter boots, gloves, and other items so they can evacuate while properly equipped.
People are encouraged to keep cash and identification with them, double-check emergency supplies, and secure furniture in case aftershocks grow stronger.
The government is now being pushed to better communicate what the advisory system means, fight misinformation more actively, and strengthen emergency response frameworks. Local governments are also being asked to review evacuation centre readiness, particularly in aging and depopulated areas where vulnerable residents may need assistance.
