An earthquake with a preliminary magnitude of 7.7 off northern Japan on Monday sparked a short-lived tsunami alert and prompted authorities to advise of a slightly higher risk of a possible mega-quake for coastal areas there.

The Cabinet Office and the Japan Meteorological Agency said there was a 1% chance for a mega-quake, compared to a 0.1% chance during normal times, in the next week or so following the powerful quake near the Chishima and Japan trenches.

Officials said the advisory was not a quake prediction but urged residents in 182 towns along the northeastern coasts to raise their preparedness while continuing their daily lives.

Prime Minister Sanae Takaichi, speaking to reporters, urged residents in the affected area to confirm their designated shelters and evacuation routes and to check emergency food and grab bags so they can run immediately when the next big one hits. “The government will do our utmost in case of an emergency,” she said.

It was the second such advisory for the region in recent months. One was issued following a 7.5-magnitude quake in December but no mega-quake occurred.

Still, Monday’s earthquake and tsunami warning were a reminder to the quake-prone area of the March 2011 disaster that ravaged large swaths of the northern coast, triggering a nuclear crisis in Fukushima.

The Fire and Disaster Management Agency said two people, one in Aomori and another in Iwate, were injured after falling Monday.

The quake occurred off the coast of Sanriku at around 4:53 p.m. (0753 GMT) Monday, at a depth of about 19 kilometers (11 miles), the meteorological agency said.

Footage on NHK television showed hanging objects swaying and people squatting at a shopping center in Aomori, as authorities told people to seek higher ground and stay away from coastal areas.

Shinkansen bullet trains connecting Tokyo and northern Japan were temporarily suspended, leaving passengers in cars and on platforms waiting for service to resume.

A tsunami of about 80 centimeters (2.6 feet) was detected at the Kuji port in Iwate prefecture within an hour of the quake, and a smaller tsunami of 40 centimeters (1.3 feet) was recorded at another port in the prefecture, the meteorological agency said.

The U.S.-based Pacific Tsunami Warning Center later said the tsunami threat “has now passed.” Hours later, Japan also lifted all tsunami alert and advisories.

The Nuclear Regulation Authority said nuclear power plants and related facilities in the region were intact and no abnormalities were detected.

The disaster management agency said at one point, more than 180,000 people in five northern prefectures from Hokkaido to Fukushima were advised to take shelter.

It’s 15 years since a magnitude 9.0 earthquake and tsunami on March 11, 2011, ravaged parts of northern Japan, causing more than 22,000 deaths and forcing nearly half a million people to flee their homes, most of them due to tsunami damage.