Japan Issues Mega-Quake Advisory After 7.7 Earthquake Triggers Tsunami Alert

Tokyo – A powerful 7.7-magnitude earthquake off northern Japan on Monday briefly triggered a tsunami alert and prompted authorities to warn of a heightened, though still low, risk of a potential mega-quake along the country’s northeastern coast.

According to the Japan Meteorological Agency and the Cabinet Office of Japan, the probability of a mega-quake occurring within the next week has risen to 1%, compared to the usual 0.1% baseline risk. Officials stressed that the advisory is not a prediction, but a precautionary measure following the strong seismic activity near the Chishima and Japan trenches.

The earthquake struck off the Sanriku coast at approximately 4:53 p.m. local time, at a depth of about 19 kilometres. A tsunami measuring 80 centimetres was recorded at Kuji Port in Iwate Prefecture, while a smaller 40-centimetre wave was detected at another nearby port.

The Pacific Tsunami Warning Center later confirmed that the tsunami threat had passed, with Japan subsequently lifting all warnings and advisories.

The Fire and Disaster Management Agency reported that at least two people were injured, one in Aomori and another in Iwate, after falling during the quake. Transport services were also disrupted, with Shinkansen bullet trains temporarily suspended, leaving passengers stranded on platforms and inside train cars until operations resumed. Local broadcaster NHK aired footage showing buildings shaking, hanging objects swaying, and people crouching in shopping centres as tremors were felt across the region.

Prime Minister Sanae Takaichi urged residents in 182 coastal towns to review emergency preparedness measures, including evacuation routes, shelters, and essential supplies.

“Residents should confirm their evacuation plans and be ready to act immediately if necessary,” she said. “The government will do our utmost in case of an emergency.”

Authorities advised more than 180,000 people across five northern prefectures from Hokkaido to Fukushima to seek shelter at the height of the alert. Japan’s Nuclear Regulation Authority confirmed that no abnormalities were detected at nuclear power plants in the affected areas, easing concerns of a repeat of past disasters.

The latest quake has revived memories of the devastating 2011 Tōhoku earthquake and tsunami, which killed more than 22,000 people and triggered the Fukushima nuclear crisis.

While no major damage has been reported from Monday’s quake, experts say such events highlight Japan’s ongoing vulnerability as one of the world’s most earthquake-prone nations.

Seismologists emphasise that aftershocks and related seismic activity remain possible in the coming days, reinforcing the need for vigilance.

Japan earthquake 7.7