Japan lifts megaquake advisory week after powerful tremor

Japan has lifted a rare warning over the risk of a potential megaquake, one week after a strong earthquake struck off the country’s northern coast, the national weather agency said on Tuesday, while cautioning that seismic dangers have not disappeared.

The magnitude-7.5 earthquake hit on December 8, triggering tsunami waves of up to 70 centimetres and injuring more than 40 people. Despite the strength of the tremor, authorities reported no major structural damage. The Japan Meteorological Agency (JMA) and the Fire and Disaster Management Agency said emergency responses helped limit the impact, even as coastal communities briefly braced for larger waves.

In the aftermath of the quake, the JMA issued a rare advisory warning of an elevated risk of a so-called megaquake — defined as an earthquake of magnitude 8.0 or greater — in northern Japan. Such advisories are uncommon and are issued when scientific data suggests a temporary increase in the likelihood of a much larger seismic event.

Scientists note that following an earthquake of magnitude 7.0 or above, there is roughly a one percent chance of a megaquake occurring within the following seven days. The advisory urged residents to remain alert, review evacuation routes and prepare emergency supplies in case a rapid response became necessary.

That special warning period officially expired at midnight, JMA official Issei Suganuma told AFP on Tuesday. “But it doesn’t mean that quakes will not happen again, so we’d like residents to remain vigilant,” he said, emphasizing that Japan remains one of the most seismically active countries in the world.

The JMA added that while there is still a heightened risk of a megaquake occurring off the northern coast, the probability is expected to decline gradually as more time passes without further major tremors.

Government disaster prevention guidelines released in March underscore the potential scale of such a scenario. An offshore megaquake in the Hokkaido–Sanriku region — the area covered by the advisory — could generate tsunami waves as high as 30 metres. Officials estimate that such an event could kill up to 199,000 people, destroy as many as 220,000 buildings and cause economic damage reaching 31 trillion yen, or about $200 billion.

Authorities continue to urge preparedness, warning that Japan’s seismic risks demand constant readiness rather than complacency.