Japan issues first ever ‘megaquake’ warning after 7.1-magnitude tremor

Japan is bracing for a long feared megaquake after a powerful 7.1-magnitude tremor caused tsunami waves to hit some regions.

Japan has been warned to brace for a megaquake after a powerful magnitude 7.1 tremor prompted tsunami waves.
The Japan Meteorological Agency has warned there is now a “relatively higher” probability than usual of a long-feared megaquake occurring around the Nankai Trough, but added that it shouldn’t be taken to signal such an event is imminent.

The government has said the potential megaquake, with an estimated magnitude of 8-9, has a roughly 70 per cent probability of striking within the next 30 years.

A building shakes during a 7.1-magnitude earthquake in Japan on Thursday. Picture: Supplied

It could affect a large swath of the Pacific coastline of Japan and threaten an estimated 300,000 lives in the worst-case scenario, experts say.

The advisory “doesn’t mean the megaquake will definitely happen during a certain period of time”, JMA official Shinya Tsukada told reporters.

Thursday’s quake hit at 4.42pm (5.42pm AEST) off the southern island of Kyushu at a depth of 25km, the United States Geological Survey said.

The USGS had initially reported two strong quakes, with magnitudes of 6.9 and 7.1, but later said there had only been one tremor.

Power lines rattled during the 7.1-magnitude earthquake in southern Japan. Picture: Supplied

The Japan Meteorological Agency (JMA) also said there was one quake with a magnitude of 7.1.

Broadcaster NHK showed footage of traffic lights shaking violently in Miyazaki on Kyushu’s southeast coast.

“The surface of the sea is wavering. I felt an intense jolt when the quake happened which lasted for between 30 seconds and a minute,” one local official told NHK.

Government spokesman Yoshimasa Hayashi said officials were notified of one minor injury and two other unspecified injuries.

No disruptions to infrastructure, including electricity, water and telecommunications, were reported, Hayashi added.

Unverified footage shared on social media showed only minor damage, including dishes and books that had fallen off shelves and a small wall that had collapsed in a car park.

Japan’s NHK public television said windows were broken at the Miyazaki airport near the epicenter of Thursday’s tremor. The airport’s runway was temporarily closed for safety checks.

Tsunamis of up to one metre were initially expected to arrive or had arrived in some coastal areas in Kyushu and Shikoku islands, the JMA said.

The agency also said a small tsunami was possible in Chiba, about 850km from the epicentre.

“Tsunamis will strike repeatedly. Please do not enter the sea or approach the coast until the warning is lifted,” the JMA said on social media platform X.

The location of Thursday’s tremor. Picture: Anadolu via Getty Images

However, tsunamis of only 50cm, 20cm and 10cm were confirmed to have hit some places, including the port of Miyazaki, more than an hour after the quake, it said.

The Pacific Tsunami Warning Center issued a warning that said hazardous tsunami waves were possible within 300km of the epicentre.

No abnormalities were reported at atomic power plants in the area, according to the nuclear regulation authority.

The country also routinely holds emergency drills to prepare for a major quake.

At least 318 people were killed when an earthquake hit the Noto peninsula on the Sea of Japan side of the main island of Honshu on New Year’s Day.

The January 1 quake and its aftershocks toppled buildings, caused fires and knocked out infrastructure.

In 2011, a colossal 9-magnitude undersea quake off northeastern Japan triggered a tsunami that left around 18,500 people dead or missing.

It sent three reactors into meltdown at the Fukushima nuclear plant, causing Japan’s worst post-war disaster and the most serious nuclear accident since Chernobyl.

The capital Tokyo was devastated by a huge earthquake a century ago in 1923.

- with AFP