On January 15, the Japanese government’s Earthquake Investigation and Research Committee announced that the likelihood of a mega earthquake occurring in the Nankai Trough within the next 30 years has risen to around 80%.
Each January, Japan recalculates the probability of a mega earthquake in the Nankai Trough. The earthquake probability is calculated based on the length of time between past earthquakes and the number of years since the last one.
The probability of a mega earthquake in the Nankai Trough increases by less than 1% each year. Since 2018, the probability of a magnitude 8 to 9 earthquake occurring along the Nankai Trough has been estimated to be 70% to 80%.
As of January 1 this year, through various scenario calculations, the probability of a mega earthquake occurring is in the range of 75% to 82%. This probability is usually rounded, and this time it has been revised to approximately 80%.
Since the earthquake in the Noto Peninsula in central Japan on January 1, 2024, Japan has experienced multiple earthquakes with a magnitude reaching or exceeding 6.0 on the Richter scale. The Chairman of the Earthquake Investigation Committee and Honorary Professor at the University of Tokyo, Naoshi Hirata, stated that this level of earthquake activity had not been observed before, making it “difficult to predict when it will weaken”. He emphasized the need to remain vigilant as the active earthquake activity may continue for some time.
Earlier this week, following a 6.6 magnitude earthquake in southwest Japan, the Japan Meteorological Agency issued a second supplementary information regarding the Nankai Trough.
Despite the tremors occurring beneath the assumed epicenter of the Nankai Trough earthquake on the western edge, the Meteorological Agency did not issue a special warning as it believed the risk of a mega earthquake occurring would not immediately increase.
Following a 7.1 magnitude earthquake off the coast of Miyazaki Prefecture on August 8, 2024, the Japanese government issued a warning for a Nankai Trough earthquake, marking the first time since the system was implemented in 2017.
The Nankai Trough is a submarine trench extending along the Pacific coast of Japan where the Eurasian and Philippine Sea plates converge. A mega earthquake occurs approximately every 100 to 150 years in this region, with the most recent major earthquake being the 1946 Nankai Earthquake (magnitude 8.1).
As a country prone to frequent earthquakes, Japan has long been concerned about the potential for an 8 to 9 magnitude earthquake in the Nankai Trough, predicting widespread areas to be affected by shaking and vast coastal regions at risk of being engulfed by massive tsunamis.