Japan’s Overdue Centennial Earthquake

January 27th, 2025

Mira Carpenter

Along the Nankai trough, a seismic border 900 km off the southeastern coast of Japan, seismic activity brews continually. This is a major zone where the Philippine Seat Plate meets the Eurasian Plate, a zone that produces Japan’s most disastrous earthquakes. Every 90-100 years, Japan suffers from a cataclysmic earthquake chain reaction that affects Tokyo and rural provinces alike. This activity leads to magnitude 8-9 earthquakes that often occur in pairs, such as the 1944 and 1946 quakes. Though Japan sits on the “ring of fire” and experiences about 1500 annual quakes, most are minor.

However, Nankai megathrust quakes often result in major volcanic activity (Mt. Fuji eruption in 1707 which killed 5,000) and tsunamis (1944 tsunami that killed 1,362 people and damaged 36,000 houses) as well as multiple nuclear reactor meltdowns. If all the edge borders of the Nankai trough slip under the surrounding tectonic plates, the trough has the ability to produce a 9.1 magnitude earthquake.

Last week, the government has raised its estimate that the likelihood of a Nankai megathrust in the next 30 years to 80%. At the time of the estimate’s introduction in 2013, this likelihood was placed at 60-70%, as reported by the Headquarters for Earthquake Research Promotion (HERP), a Japanese government earthquake research panel. This comes after the magnitude 6.8 quake that hit Japan last week on January 13th.

The implications of such an earthquake are always disastrous, but 2025 brings new strife that would complicate events further. The Eurasia Group Top Risks for 2025 cite Japan’s biggest liabilities as hurdles for Japanese diplomacy. Japan faces trade spats, inflationary pressure, and a volatile yen, but the global Top Risk #4 of Trump tariffs and economic changes would decimate Japan’s auto-based economy. Top Risk #3 of a U.S.-China breakdown (Japan’s top trading partners) would send aftershocks into Japan. With an impending Nankai megathrust earthquake that would require billions to fix damages, economic turmoil on the horizon is a massive threat to the entire country’s ability to stay afloat. Time will tell when the next Nankai quake will hit, but as the likelihood predictions creep higher and higher, trouble is on the horizon for the land of the rising sun.