Nankai Trough megaquake probability raised to 80% after M6.8 Kyushu earthquake, Japan
Japan has increased the estimated probability of a magnitude 8 and 9 megaquake occurring in the Nankai Trough within the next 30 years to around 80% on January 16, 2025, after an M6.8 earthquake hit near the coast of Kyushu. The probability was previously estimated at 70 to 80%.
Image credit: TW/SAM, Google
Headquarters for Earthquake Research Promotion (HERP), a Japanese government earthquake research panel, has increased the estimated probability of a magnitude 8 and 9 megaquakes occurring in the Nankai Trough within the next 30 years to around 80% after an M6.8 earthquake hit near the coast of Kyushu on January 13.
The adjustment was announced on January 16, following an annual recalculation of earthquake probabilities across Japan based on historical seismic activity. The probability was previously estimated at 70 to 80% and has been updated based on historical seismic activity trends.
The Nankai Trough, an undersea trench extending approximately 800 km (500 miles) from Shizuoka Prefecture to the southern coast of Kyushu, is a major subduction zone where the Philippine Sea Plate collides with the Eurasian Plate. It has produced some of Japan’s most destructive earthquakes often triggering powerful tsunamis along the Pacific coastline.
HERP recalculates earthquake probabilities based on the elapsed time since the last major event. The probability of a Nankai Trough megaquake was first introduced in 2013 at 60 to 70% and raised to 70% in 2014 and increased to 70 to 80% in 2018. The latest revision has now raised the probability to approximately 80%.
Naoshi Hirata, Committee chairman and professor emeritus at the University of Tokyo, clarified that the revised probability was not influenced by an abnormal seismic activity but was part of the routine annual update.
“This probability is a number indicating that it would be no surprise if an earthquake were to happen at any time,” Hirata stated.
“We’d like to ask people to continue to be prepared.”
The epicenter of the January 13 M6.8 Kyushu earthquake was 11 km (7 miles) east-southeast of Miyazaki and affected nearby cities including Saito and Tsuma. The quake resulted in minor structural damage such as a broken window at a Miyazaki railway station and bottles falling from shelves at a liquor store. Some train services were temporarily suspended and the Kyushu Shinkansen bullet train reduced speed between Kumamoto and Shin-Yatsushiro.
JMA issued a tsunami advisory shortly after the earthquake and lifted it at 23:50 LT (14:50 UTC). A tsunami wave of 20 cm (7.9 inches) was observed in Miyazaki while Kochi recorded a 10 cm (4 inches) wave. The Sendai nuclear power plant in Kagoshima Prefecture reported no irregularities with radiation levels remaining stable.
Yamashita Yusuke, Assistant Professor of Kyoto University’s Disaster Prevention Research Institute, analyzed the event, stating that the earthquake occurred near the location of an M7.1 quake in the Hyuganada Sea in August 2024. He suggested that movement in a previously cracked section may have caused the latest earthquake but noted that it is unlikely to influence the potential for a future Nankai Trough megaquake. He also pointed out that the seismic energy released was approximately half that of the August 2024 earthquake.
JMA and the Geospatial Information Authority of Japan held a press conference on January 14 and explained that the earthquake originated in a tectonic boundary near the western edge of a potential Nankai Trough megaquake zone. They reaffirmed that this event was part of ongoing regional seismic activity and urged the public to stay prepared for possible further earthquakes in the coming week.
An M7.1 earthquake in the same region prompted JMA to issue its first-ever Nankai Trough Earthquake Extra Information advisory on August 8, 2024, and warned of an increased probability of a major event. Such advisories are designed to inform the public of potential seismic risks under new protocols established in 2019, without necessarily predicting an imminent disaster.
The Nankai Trough has a history of producing megaquakes. The most severe recorded event occurred in 1707 when all segments of the trough ruptured and triggered widespread destruction and the last known eruption of Mount Fuji.
Large earthquakes struck in pairs in 1854 and 1944 to 1946.
References:
1 80% chance of Nankai Trough megaquake within 30 years – The Asahi Shimbun – January 16, 2025
2 Chance of Japan’s Nankai Trough megaquake raised to 80%: government panel – Kyodo News – January 16, 2025
3 Possibility of Nankai Trough megaquake now 80%, government panel reports – the japan times – January 16, 2025
Rishika holds a Master’s in International Studies from Stella Maris College, Chennai, India, where she earned a gold medal, and an MCA from the University of Mysore, Karnataka, India. Previously, she served as a Research Assistant at the National Institute of Advanced Studies, Indian Institute of Science, Bengaluru, India. During her tenure, she contributed as a Junior Writer for Europe Monitor on the Global Politics website and as an Assistant Editor for The World This Week. Her work has also been published in The Hindu newspaper, showing her expertise in global affairs. Rishika is also a recipient of the Women Empowerment Award at the district level in Haryana, India, in 2022.
“Thus says The Lord God: The earth is filled with violence, the whole world is corrupt! Madness has overcome the people, transgression is uplifted, and abominations of every kind are widely accepted; great wickedness proliferates throughout every tribe, tongue, people and nation unimpeded! Thus the earth is forsaken for a time, wherein I have turned to it My back. And so shall it remain, until the Great Day comes when I shall move swiftly against it…
And until this time and after, the earth shall tremble and shake, and bring forth calamity upon calamity, and famine and pestilence of every kind. For all this is but the beginning of sorrows, the first contractions of an expectant mother suffering to bring forth… Says The Lord.”
(From The Volumes of Truth, Volume Seven, excerpts from “The World Shall Be Shaken”)
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