Japan under tsunami warning after M7.7 quake, officials cite a 1% chance of a second 'mega‑quake'

A magnitude 7.7 earthquake struck off northern Japan and prompted tsunami advisories, with the Japan Meteorological Agency reporting wave heights up to about 1 meter along parts of the coast; officials also said there is roughly a 1% chance of a larger 'mega‑quake' in the coming week.

A magnitude 7.7 earthquake occurred early Monday about 62 miles (100 kilometers) off northern Japan, and authorities issued tsunami advisories for much of the Pacific coastline. The Japan Meteorological Agency confirmed tsunami arrival along stretches from Fukushima to Hokkaido and reported observed wave heights of roughly 0.2 to 0.8 meters, with a forecast maximum near 1 meter. Officials reported that tens of thousands of people were urged away from the shore and that aftershocks were expected. National agencies also said there is an increased short‑term chance of a larger "mega‑quake" compared with normal background levels. What is known now: - Magnitude and location: A 7.7 magnitude earthquake struck about 62 miles (100 kilometers) off northern Japan, reported early Monday. - Tsunami observations: The Japan Meteorological Agency confirmed initial tsunami arrivals from Fukushima to Hokkaido and along the Japan Sea coast of Aomori, with observed wave heights around 0.2–0.8 meters and a predicted maximum near 1 meter. - Public alerts: Officials reported that residents in affected areas were urged away from the shore and that tens of thousands received notices to move to higher ground. - Seismic risk: Aftershocks were described as likely, and the Cabinet Office and the Japan Meteorological Agency reported about a 1% chance of a larger "mega‑quake" in the next week, versus a lower baseline at normal times. - International impact: The U.S. Tsunami Warning System reported the event posed no danger to U.S. coastlines. Summary: The earthquake prompted tsunami advisories and confirmed tsunami arrivals with modest wave heights along parts of Japan's coast, and authorities reported wide monitoring of the situation. Officials also noted an elevated short‑term chance of a larger quake in the coming week. Undetermined at this time.