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98-ft tsunami, can kill 1,99,000: What's behind Japan's rare ‘megaquake’ advisory
Japan authorities hope the alert will encourage residents to prepare for the worst, recalling the 2011 catastrophe that killed nearly 20,000 people.
Japan on Tuesday issued a rare “megaquake advisory” after a magnitude 7.5 earthquake struck off the eastern coast of Aomori, just south of Hokkaido.
While the quake caused only modest damage, 34 mostly mild injuries and limited impact on roads and buildings, officials said the tremor temporarily raised the risk of a much larger quake in the region, according to the Associated Press. Officials added that the advisory is not a forecast. The likelihood of a magnitude 8 or stronger earthquake remains low, about a per cent.
But authorities hope the alert will encourage residents to prepare for the worst, recalling the 2011 catastrophe that killed nearly 20,000 people and triggered the Fukushima nuclear disaster.
Japan’s Meteorological Agency (JMA), as reported by AP, said there is an elevated chance of a powerful, magnitude-eight-plus quake within the next week. Residents in coastal belts have been urged to stay alert, keep emergency kits ready and evacuate quickly if needed.
Why Japan's north is at higher risk
The JMA says Monday’s quake increased seismic risks along the Hokkaido-Sanriku coast, where the Pacific Plate dives beneath Japan, forming the Japan Trench and Chishima Trench — zones responsible for many of the country’s largest historic earthquakes.
Experts cited by AP news agency, said that the devastating 2011 earthquake and tsunami were caused by movement along the same Japan Trench.
The JMA also pointed out that the 2011 magnitude 9.0 megaquake was preceded just two days earlier by a magnitude 7.3 temblor in the same zone, similar to the pattern seen this week.
The 2011 tsunami, which reached 15 metres (50 feet) in some areas, ravaged coastal communities in Iwate, Miyagi and Fukushima and destroyed the Fukushima Daiichi nuclear plant, leaving deep, long-lasting fears over radiation exposure.
What a future megaquake could look like
Government estimates, cited by the news agency, warn that another offshore megaquake in the Hokkaido–Sanriku region could unleash a 30-metre (98-foot) tsunami, kill up to 1,99,000 people, destroy 2,20,000 structures and cause nearly 31 trillion yen ($198 billion) in economic losses.
Up to 42,000 people could also suffer hypothermia if such a disaster occurs in winter.
The current advisory spans 182 municipalities from Hokkaido down to Chiba Prefecture — one of the widest geographical alerts issued in recent years.
This week’s advisory is more cautious and specific than a similar one issued last year. In summer 2024, a broad “Nankai Trough” megaquake advisory for southern Japan triggered public anxiety, panic buying and widespread event cancellations because of its ambiguity.
(With AP inputs)
