Japan warns: Probability of Nankai super earthquake could exceed 90%

More than a decade after the 2011 earthquake and tsunami disaster that caused a serious nuclear crisis, Japan is 'nervous' about a new warning: the Nankai Trench could have a super earthquake at any time.

Downtown Shimoda, Shizuoka Prefecture, central Japan, in this photo taken in June 2025. This area could be hit by a tsunami as high as 31m if a major earthquake occurs in the Nankai Trench - Photo: MAINICHI

On September 26, the Japanese Government 's Earthquake Investigation Committee said that the probability of a mega-earthquake occurring in the Nankai Trench within the next 30 years has been adjusted from 80% to about 60-90% or higher.

The Japan Earthquake Investigation Committee explained that the adjustment reflects a new calculation method that takes into account data errors and forecast uncertainties. The adjustment does not mean that the risk of earthquakes has increased.

"The current situation remains: an earthquake can happen at any time. We call for continued efforts to strengthen disaster preparedness," said Naoshi Hirata, chairman of the committee and emeritus professor at the University of Tokyo, as quoted by Kyodo News Agency.

In 2013, the committee put the probability of a megaquake at 60-70%, based on the spacing between past earthquakes and data recording crustal uplift at Murotsu port in Kochi prefecture (Shikoku island), which was linked to three major events since the 1700s. This number was then gradually raised over time, to about 80% by January 2025.

In the latest revision, the committee incorporated new research results, which showed that the data on the Murotsu crustal uplift phenomenon was erroneous.

Using a new calculation method, estimating probabilities based on limited data, the committee came up with a probability of about 60-90% or higher, for the possibility of a megaquake occurring within the next three decades.

Another calculation method that did not use data on crustal uplift gave a result of between 20 and 50%. However, the committee decided to emphasize the higher probability, in order to encourage disaster preparedness.

The Nankai Trench is a deep undersea canyon that runs along the Pacific coast of Japan, where the Eurasian and Philippine Sea tectonic plates meet.

It is believed that megathrust earthquakes occur every 100-150 years along this trench. About 80 years have passed since the Tonankai (1944) and Nankai (1946) earthquakes - the most recent events confirmed to be related to this trench.

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Source: https://tuoitre.vn/nhat-ban-canh-bao-xac-suat-xay-ra-sieu-dong-dat-nankai-co-the-vuot-90-20250926193117489.htm