Japan’s government has issued a severe warning that up to 199,000 people could perish if an earthquake of massive proportions triggers a major tsunami along the Japan and Chishima trenches.
The alert comes after a magnitude 7.5 earthquake struck off the eastern coast of Aomori Prefecture on 8 Dec 2025, registering an upper six on Japan’s seismic intensity scale.
First-Ever Subsequent Earthquake Advisory Raises Alarm
In response to the 8 Dec quake, the Japan Meteorological Agency (JMA) issued a “subsequent earthquake advisory,” noting that the likelihood of a megaquake in the same region had risen.
This marked the first time since the advisory system was introduced in 2022 that JMA has issued such a warning.
The advisory covers 182 municipalities across seven prefectures and urges residents to stay vigilant. Residents should prepare for possible evacuation and review safety measures while continuing daily activities.
JMA emphasized 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 trigger tsunamis impacting 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 been responsible for many significant quakes over the years.
Historical Patterns Point to Imminent Catastrophe
According to the Central Disaster Management Council, maximum-class tsunamis have occurred along the trenches at intervals of about 300 to 400 years.
The most recent occurrence is thought to have been in the 17th century.
Experts believe a maximum-class earthquake and tsunami are imminent.
The council’s 2021 damage projection estimated that a magnitude-nine earthquake along the Japan Trench, with tsunamis surging on the Pacific Coast from Hokkaido to Chiba on a winter night, could result in 199,000 deaths.
Heavy snow during winter could hinder evacuations, compounding the death toll.
A similar event along the Chishima Trench could kill 100,000 people.
Even among those who successfully evacuate, an estimated 42,000 face an increased death risk due to hypothermia after a Japan Trench quake and 22,000 after a Chishima Trench quake.
Preparation Measures Could Slash Death Toll by 80 Per Cent
The council stressed that fatalities could be reduced by 80 per cent if people are able to reach higher ground promptly through improved tsunami evacuation awareness.
The risk of hypothermia could be eliminated 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.
Individuals 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 urged to better communicate the significance of the advisory system, bolster efforts against misinformation, and strengthen emergency response frameworks.
Local governments are also being asked to review evacuation centre readiness, particularly in ageing and depopulated areas where vulnerable residents may require assistance.
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