Japan Issues Megaquake Advisory After 7.7-Magnitude Earthquake Off Northeastern Coast

Japan has issued an advisory for a slightly higher risk of a possible megaquake following a 7.7-magnitude earthquake that struck off the northeastern coast on Monday, April 20, 2026. The quake, which occurred off the coast of Sanriku at a depth of about 19 kilometers, prompted a short-lived tsunami alert and led authorities to urge residents in 182 towns along the coast to raise their preparedness while continuing daily life.

The Japan Meteorological Agency said there is now a 1% chance of a megaquake — defined as an earthquake measuring 8.0 or higher — in the next week or so, compared to a 0.1% chance during normal times. Officials emphasized that the advisory is not a prediction but a precautionary measure to encourage vigilance.

Prime Minister Sanae Takaichi urged residents to confirm evacuation routes, check emergency supplies, and identify designated shelters. “The government will do our utmost in case of an emergency,” she said, adding that two people were injured in Aomori and Iwate prefectures after falling during the quake.

Tsunami waves reached heights of 80 centimeters, and while no major damage or abnormalities at nuclear facilities were reported, the UN’s nuclear watchdog confirmed it had been informed by Japanese officials that no issues occurred at the country’s nuclear sites. The undersea activity triggered tremors as far as Tokyo, approximately 530 kilometers south.

Although tsunami warnings were later downgraded to advisories — the lowest level — authorities continue to advise the public to remain away from the coast. The Japan Meteorological Agency noted that the country remains on high alert for aftershocks.

This marks the second such megaquake advisory for the region in recent months, following a similar notice after a 7.5-magnitude quake in December 2025, which did not result in a larger event. Officials reminded the public of the March 2011 disaster, which devastated northern Japan and triggered a nuclear crisis in Fukushima, as a reminder of the region’s seismic vulnerability.

As of now, there have been no reports of Indonesian casualties related to the earthquake, and evacuation orders affecting approximately 170,000 people have been eased as the immediate tsunami threat diminished.