The Japanese government’s earthquake investigation panel has raised concerns about the increased likelihood of a devastating earthquake along the Nankai Trough. According to NHK, experts now estimate an 80% chance of a magnitude 8-9 quake occurring within the next 30 years.

Over a 40-year period, the probability rises to 90%, and in the next 50 years, it exceeds 90%. This projection stems from detailed recalculations conducted annually in January.

Nankai Trough: A high-risk seismic zone

The Nankai Trough, located southeast of Honshu Island, lies along the boundary where the Philippine Sea tectonic plate subducts beneath Japan's Eurasian plate. This area has a history of subduction megathrust earthquakes, with intervals of 100 to 200 years. The last major earthquake here was recorded in 1946.

Government studies warn that a megaquake in the Nankai Trough could result in catastrophic damage, including massive tsunamis capable of swamping coastal areas within minutes. Smaller islands could face waves over 30 meters high. Densely populated areas on Honshu and Shikoku could be significantly impacted, potentially causing 323,000 fatalities and billions of dollars in economic losses.

Recent seismic activity raises concerns

Japan has experienced notable seismic activity recently, further heightening concerns. On January 13, a magnitude 6.4 earthquake struck near Kyushu Island, with tremors felt as far as Hiroshima and Osaka. Earlier, on August 8, 2024, a magnitude 7.1 quake off Miyazaki Prefecture prompted the Japan Meteorological Agency (JMA) to issue a Nankai Trough advisory, its first since 2017.

The panel’s chairman, Professor Emeritus Naoshi Hirata of the University of Tokyo, emphasized that this heightened seismic activity is unprecedented. "It’s difficult to predict when this phase will subside, making vigilance essential," he stated.

Historical context and preparedness

Over the past 1,400 years, the Nankai Trough has produced several megaquakes, including the 1707 rupture that triggered Japan's second-most powerful earthquake on record and the eruption of Mount Fuji. Subsequent quakes in 1854, 1944, and 1946 further underscore the region's seismic volatility.

In response, Japan continues to refine its disaster preparedness systems. Since 2011’s Tohoku earthquake and tsunami, new advisory rules have been implemented. However, false alarms, such as last year’s temporary megaquake advisory, have led to public panic and supply shortages.

The Japanese government and experts urge residents to remain vigilant, emphasizing the critical need for readiness in the face of an increasingly probable natural disaster.