Nankai Trough 'megaquake' could kill 300,000 people: Japan acknowledges risk, ramps up measures

The Japanese government has announced that it would improve preparedness measures for a future Nankai Trough "megaquake" that could kill up to 300,000 people. Earlier in January 2025, an assessment had raised the chances of a megaquake, an earthquake of magnitude 8, hitting the region within the next 30 years to 75–82 per cent. Then in March, the new national impact estimate noted that such an event, accompanied by a tsunami, could cause widespread devastation, and result in 298,000 deaths and damages worth $2 trillion. The Nankai Trough is a roughly 800 km undersea trench and a subduction zone where the Philippine Sea Plate is being pushed beneath Japan. It has been making headlines after Ryo Tatsuki, Japan's Baba Vanga, issued an ominous warning for the region in a 1999 manga comic. Also Read: Ryo Tatsuki and the 15-year cycle: Stressing over July 5? Her pattern of predictions will calm you down

What did Ryo Tatsuki write in the manga comic for Japan and July 5?

Tatsuki's prophecy triggered fear, leading people to cancel their tickets to Japan. According to Tatsuki, "a crack will open up under the seabed between Japan and the Philippines," and trigger massive waves that would be taller than the 2011 tsunami generated by the Great East Japan Earthquake that slammed Tōhoku. "The Ocean floor between Japan and the Philippines will crack. Huge waves will rise in all directions. Tsunamis will devastate the Pacific Rim countries. A tsunami three times higher than that of the Great East Japan Earthquake of March 2011 will strike the southwest of the country," a passage of the book reads. However, the Japan Meteorological Agency (JMA) has rubbished it all as unscientific. Also Read: Japan 'megaquake' coming? Earthquakes detected at exact point Ryo Tatsuki predicted in manga comic book
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Nankai Trough scare of a megaquake

This region in Japan has typically witnessed large-magnitude earthquakes for over 1,400 years. Records suggest that a megaquake has struck the Nankai Trough every 100 to 200 years. The last one was in 1946 when an earthquake of magnitude 8.1 to 8.4 occurred in Northern Honshū to Kyūshū. Nearly 36,000 homes were destroyed in southern Honshū, and the earthquake resulted in 16–to 20-foot tsunami waves. The January and March reports have led the Japanese government to take notice and admit that much more needs to be done to avoid a major tragedy in the Nankai Trough area in the event of a megaquake striking in the next three decades. Also Read: Amid manga scare, Japanese island village jolted by 1,031 earthquakes evacuated overnight

On July 2 2025, an updated preparedness plan was released, which recommended speeding up the construction of embankments and evacuation buildings, frequency of public drills to be increased, and coordinated action by all levels of government, businesses, and non-profit organisations. Prime Minister Shigeru Ishiba called on all sectors to work together to save as many lives as possible.