A powerful offshore earthquake jolted northern Japan on Monday, briefly triggering a tsunami alert and reviving concern along a coastline still marked by memory and risk.

Authorities said the quake, measured at magnitude 7.7 by Japanese officials and 7.4 by the United States Geological Survey, struck off the Sanriku coast at around 4:53 p.m. The tremor originated at a depth of about 19 kilometers, sending noticeable shaking across parts of the region, including Aomori and Iwate prefectures.

For a short period, residents were urged to move to higher ground as precautionary tsunami alerts were issued. Waves were later observed, with about 80 centimeters recorded at Kuji port and smaller surges elsewhere. The warnings were eventually lifted after officials assessed the immediate risk had passed.

Still, the event prompted a more measured advisory from the Cabinet Office and the Japan Meteorological Agency. They raised the likelihood of a potential megaquake in the coming week to 1%, up from the usual 0.1%. Officials were careful to stress that this is not a prediction, but rather an indication of elevated probability following significant seismic activity.

The advisory covers 182 municipalities along the northeastern coastline. Residents have been asked to review evacuation routes, confirm shelter locations, and ensure emergency supplies are ready, while otherwise continuing daily routines.

Prime Minister Sanae Takaichi echoed that message, urging preparedness without alarm. Government agencies, she said, are ready to respond if conditions worsen.

The quake caused limited disruption but served as a sharp reminder of the region’s vulnerability. Bullet train services between Tokyo and northern Japan were temporarily halted, leaving passengers waiting on platforms and inside train cars until operations resumed.

Local media footage showed people reacting instinctively to the shaking, crouching or steadying themselves as objects swayed overhead in public spaces.

Emergency services reported two injuries linked to falls during the tremor, one each in Aomori and Iwate. No major structural damage was immediately reported.

Officials also confirmed that nuclear facilities in the affected areas showed no abnormalities following inspections.

This was the second time in recent months that such an advisory has been issued. A similar alert followed a 7.5-magnitude quake in December, though no larger event materialized afterward.