Japan warns of huge earthquake after powerful tremor triggers tsunami warning

Japan warned of a heightened threat of a magnitude 8.0 earthquake or stronger after a powerful offshore jolt struck the country’s north, sending authorities scrambling to issue a tsunami alert.

In a statement, the Japan Meteorological Agency (JMA) said that “the likelihood of a new, huge earthquake occurring is relatively higher than during normal times”.

The advisory for the northern region was issued hours after a 7.7-magnitude earthquake hit the area, shaking high-rise buildings in Tokyo, hundreds of kilometres from the epicentre.

The quake struck at 4.53pm (8.53am Irish time) in Pacific waters off northern Iwate prefecture. Officials first put its magnitude at 7.4, then revised it to 7.5 and later again to 7.7.

Within two hours of the earthquake, tsunami waves reaching 80cm had been recorded, while warnings stayed in place over the risk of larger surges along the northern tip of Japan’s main island of Honshu and in the Hokkaido region.

Several port towns, including Otsuchi and Kamaishi – both devastated by the 2011 earthquake and tsunami – earlier ordered thousands of residents to evacuate, public broadcaster NHK reported. Bullet train operations were suspended and some motorways were shut because of the shaking.

At a separate televised briefing, a Cabinet Office official said that “while it is uncertain whether (another) major earthquake will actually occur, we ask that you take disaster preparedness measures based on the principle that you are responsible for your own safety”.

The ⁠quake registered an ‘upper 5’ on Japan’s seismic intensity scale, a level strong enough to make movement difficult and to bring down un-reinforced concrete-block walls. JMA said the tremor had ⁠an epicentre ‌in the Pacific Ocean and was 10km (six miles) deep.

According to JMA, a three-metre tsunami could damage low-lying areas by inundating buildings and sweeping away anyone caught in the currents.

Set on the Pacific “Ring of Fire”, a vast zone of volcanoes and ⁠oceanic trenches, Japan is among the most earthquake-prone nations in the world, experiencing a ⁠tremor at least every five minutes.

The country accounts for about 20% of the world’s earthquakes measuring magnitude 6.0 or higher, including the 2011 catastrophe that triggered nuclear meltdowns at the Fukushima power plant.

No nuclear power plants are currently operating in the affected areas, and Hokkaido Electric Power Co and Tohoku Electric Power Co said no abnormalities had been reported at their facilities ‌there.

Japan haunted by memory of massive 9.0-magnitude quake in 2011

Japan still lives with the trauma of the huge 9.0-magnitude undersea quake in 2011, which unleashed a tsunami that killed around 18,500 people and caused the catastrophic meltdown at the Fukushima nuclear plant.

In 2024, the JMA issued its first special advisory warning of a possible “megaquake” along the Nankai Trough.

The 800km undersea trench marks the point where the Philippine Sea oceanic tectonic plate is “subducting” – or gradually slipping – beneath the continental plate on which Japan sits.

The government has said that an earthquake in the Nankai Trough, followed by a tsunami, could leave as many as 298,000 people dead and inflict up to $2 trillion in damage.

Although the JMA lifted the 2024 advisory after a week, it sparked panic-buying of essentials such as rice and led some holidaymakers to cancel hotel bookings.

A second week-long “megaquake” advisory was issued in December 2025 after a magnitude-7.5 tremor struck off the northern coast.

The 8 December earthquake produced tsunami waves of up to 70cms and injured more than 40 people, though no major damage was reported.