Screengrab from JMA

A strong magnitude 7.5 earthquake rattled northern Japan late Monday, shaking cities, injuring residents, and prompting tsunami alerts before warnings were lifted hours later. But despite calmer waters, officials say the danger isn’t over — issuing an alert for a possible megaquake in the coming days.

The quake hit off Aomori Prefecture at 11:15 p.m., with intense shaking reaching upper 6 on Japan’s 7-level scale in Hachinohe. At least six people were hurt by falls or falling objects.

Tsunamis measuring 70 cm in Iwate, 50 cm in Hokkaido, and 40 cm in Aomori were initially recorded before advisories were lifted by 6:20 a.m. Tuesday.

Authorities also reported strong long-period ground motions— slow, swaying waves that can rock high-rise buildings. Aomori’s Rokkasho village recorded class-3 movements, strong enough to make standing difficult on upper floors.

But the biggest concern now:
A government alert for a potential magnitude 8 or higher megaquake along the Japan Trench or Chishima Trench.

Officials urged residents on Japan’s Pacific coast — from Hokkaido down to Chiba — to stay alert for the next week, check evacuation routes, prepare emergency kits, and secure their homes.

Rail services were disrupted, with the Tohoku Shinkansen suspended between Morioka and Shin-Aomori for inspections. Meanwhile, ANA and JAL flights resumed normally.

Nuclear plants across the region reported no abnormalities, including Fukushima Daiichi, where TEPCO briefly paused treated water release as a precaution.

The government quickly activated its crisis center, with Prime Minister Sanae Takaichi ordering immediate damage assessment and coordinated rescue efforts.

Experts say the quake likely occurred along a plate boundary and warn that the magnitude could still be revised.

Residents are advised to stay vigilant, keep warm if evacuating — and remain ready should a stronger quake follow.