Media: Japan issues megaquake advisory after powerful 7.5 offshore tremor

Japan has issued a rare megaquake advisory for its northern regions after a magnitude-7.5 earthquake struck off the coast of Aomori, prompting officials to warn of a slightly heightened risk of an even stronger quake in the coming days.

Offshore tremor on December 8 caused limited damage — 34 mostly minor injuries and scattered reports of cracked roads and damaged buildings — but authorities stressed that the event had temporarily increased seismic pressure along nearby fault zones, The Guardian reports.

The Japan Meteorological Agency (JMA) said the probability of an additional magnitude-8 or stronger quake remains low, at around 1%, but urged residents to prepare.

Officials underlined that the alert is not a prediction, describing it instead as a precautionary measure based on patterns seen during past major disasters. In 2011, a magnitude-7.3 foreshock struck two days before the magnitude-9.0 earthquake that triggered a devastating tsunami and led to nearly 20,000 deaths.

The current advisory covers 182 municipalities across Hokkaido, Aomori, Iwate, Miyagi, Fukushima and as far south as Chiba. The region sits above the Japan Trench and Chishima Trench — two subduction zones capable of producing some of the world’s strongest earthquakes.

Government modelling shows that another major offshore quake in the Hokkaido–Sanriku corridor could generate a tsunami as high as 30 metres, potentially killing up to 199,000 people and causing economic losses of around ¥31 trillion ($198 billion).

Local authorities have issued guidance urging households to secure heavy furniture, prepare emergency go-bags with several days’ supplies, and keep shoes and helmets within easy reach. Some municipalities are reinforcing communications networks, while others are encouraging residents to sign up for emergency alerts.

Japan last issued a similar advisory in 2024 for the southern Pacific coast. The technical language used then led to confusion, panic buying and widespread event cancellations — something officials aim to avoid this time by emphasising that daily life should continue as normal, albeit with added caution.

The JMA said it will continue to monitor seismic activity closely, but stressed there is no indication of any imminent large-scale earthquake.

By Aghakazim Guliyev