A 7.7-magnitude earthquake off northern Japan on Monday set off a brief tsunami alert and prompted Japanese authorities to issue an advisory urging coastal residents to prepare for a possible megaquake in the week after the temblor, though officials emphasized it was not a prediction. The quake occurred off the coast of Sanriku at about 4:53 p.m., according to Japan’s meteorological agency, and JMA said the earthquake’s depth was about 19 kilometers.
The Japan Meteorological Agency and the Cabinet Office said the advisory covered coastal areas near the Chishima and Japan trenches and that officials assessed a 1% chance for a megaquake in the next week or so, compared with a 0.1% probability during normal times. Officials said the guidance applied to residents in 182 towns along Japan’s northeastern coasts and told people to raise preparedness while continuing their daily lives.
Prime Minister Sanae Takaichi said residents should confirm their designated shelters and evacuation routes and check emergency food and grab bags so they could act immediately if a megaquake hit. “The government will do our utmost in case of an emergency,” Takaichi told reporters, according to the report. Officials also referenced the region’s experience in 2011, when a magnitude 9.0 earthquake and massive tsunami ravaged parts of northern Japan and triggered the Fukushima nuclear crisis.
Authorities reported that the quake and tsunami prompted people to move to higher ground in parts of the north. NHK television showed objects swaying and people squatting at a shopping center in Aomori as authorities told people to seek higher ground and avoid coastal areas, the report said. The Fire and Disaster Management Agency said two people—one in Aomori and another in Iwate—were injured after falling.
Japan’s tsunami monitoring recorded water levels at ports before the alerts were lifted. The report said a tsunami of about 80 centimeters was detected at Kuji port and a smaller tsunami of 40 centimeters was recorded at another port in Iwate prefecture, after which Japan lifted all tsunami alerts and advisories.
Officials also said the tremor caused disruptions to transportation. Shinkansen bullet trains connecting Tokyo and northern Japan were temporarily suspended, leaving passengers waiting for service to resume, according to the report. The U.S. Geological Survey measured the quake at 7.4 magnitude, while Japan’s meteorological agency reported 7.7, and Japan’s Nuclear Regulation Authority said nuclear power plants and related facilities in the region were intact and no abnormalities were detected.
This was the second megaquake advisory for the region in recent months. One advisory followed a 7.5-magnitude quake in December, but no megaquake occurred, the report said.