The Imminent Threat of the Nankai Trough Earthquake with the Approaching X-Day

“I was lying in bed when suddenly, I was hit by intense shaking from side to side. The shaking lasted for about 15 seconds and repeated three times. I’ve lived for over 80 years, and this is the first time I’ve experienced such a big earthquake.”

In Yawatahama City, Ehime Prefecture, 83-year-old Ryoji Takemura, who runs a traditional Japanese confectionery shop, reflects on the earthquake. 

On the night of April 17th, shortly after 11:00 PM, a seismic event with a maximum intensity of 6- occurred, measuring a magnitude of 6.6. It struck the western parts of Ehime and Kochi Prefectures. It’s the first time in Shikoku that an earthquake with an intensity of 6 or higher has been recorded since the current seismic scale was established in October 1996. Given that it occurred within the assumed epicenter of the Nankai Trough earthquake (M8-9), which has a 70-80% probability of occurring within the next 30 years, anxiety has spread among residents in the region.

It could be considered an unusual situation. Since the beginning of this year, there have been over 10 seismic events with a magnitude of 4 or higher, including those occurring in Taiwan. However, following the earthquake in Shikoku, the government’s Earthquake Research Committee announced that no significant changes indicating an increased likelihood of a Nankai Trough earthquake have been observed. The Japan Meteorological Agency also analyzed that although seismic activity has increased, it cannot be considered significantly active. Professor Keiaki Kawada, a specialist in natural disasters and a specially appointed professor at Kansai University, criticized this assessment.

“I agree with the Japan Meteorological Agency’s analysis that this earthquake occurred due to the rupture of a fault called the normal fault within the Philippine Sea Plate, which is subducting under the Eurasian Plate. However, it is an overstatement to say that this earthquake has no relation to the Nankai Trough earthquake. Ignoring it is like saying it’s okay to disregard it. Even though we don’t know the precise details, people who hear the announcement might feel relieved and not take any precautions. The current situation is such that the Nankai Trough earthquake could happen at any time.”

The large-scale eruption that occurred at Mount Merapi in central Indonesia on April 17th also seems to be related. According to Mr. Kawa, 

“The Australian Plate is pushing the northern side of the Philippine Sea Plate. It’s natural for volcanic eruptions and earthquakes to occur in Indonesia, located at the southern end of the Philippine Sea Plate. The Philippine Sea Plate extends as far as southern Japan. It should have an influence on the earthquakes occurring in places like Taiwan and off the coast of Chiba.” 

The Nankai Trough earthquake is said to occur in the trench where the Philippine Sea Plate and the Eurasian Plate meet. The X-day appears to be rapidly approaching. Former associate professor at the University of Tokyo Earthquake Research Institute and visiting researcher at the Fukada Geological Institute, Yoshinobu Tsuji, issues a warning.

“Especially since the beginning of this year, earthquakes have been frequent in the Pacific vicinity, mainly due to significant stress buildup between the Eurasian Plate and the subducting Philippine Sea Plate. The Nankai Trough earthquake occurs approximately every 100 years. 

Moreover, preceding major earthquakes like the Showa Nankai earthquake in 1946 and the Ansei Tokai earthquake in 1854, there were M6-class earthquakes occurring frequently in the Kinki region and Shikoku. While it’s unlikely that the recent earthquakes in Shikoku directly trigger the Nankai Trough earthquake, it seems that the crisis of the Nankai Trough earthquake is approaching considerably.”

The occurrence of a massive earthquake that could kill up to 320,000 people is becoming a reality.

From the May 10 and 17, 2024 issue of FRIDAY