In a landmark move, Japan’s meteorological agency has issued its first-ever “megaquake advisory” after a powerful 7.1-magnitude earthquake struck southern Japan on Thursday. This unprecedented alert highlights the heightened risk of strong seismic activity and large tsunamis in the Nankai Trough region, a critical subduction zone along Japan’s southwest Pacific coast.
Understanding the Nankai Trough
The Nankai Trough is a significant underwater subduction zone that stretches nearly 900 kilometers. Here, the Eurasian Plate collides with the Philippine Sea Plate, causing the latter to slide beneath the former into the Earth’s mantle. This tectonic collision builds up stress that can eventually result in a megaquake—a seismic event with a magnitude exceeding 8.
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Historically, the Nankai Trough has produced large earthquakes approximately every 100 to 150 years. According to the 2023 study High Probability of Successive Occurrence of Nankai Megathrust Earthquakes, published in Nature, these quakes often occur in pairs, with the second quake typically following within two years. The most recent pair of “twin” earthquakes occurred in 1944 and 1946.
Recent Earthquake Raises Alarm
Thursday’s 7.1-magnitude earthquake, which occurred on or near the Nankai Trough, has raised concerns among experts. The United States Geological Survey confirmed the quake’s proximity to the fault line, intensifying fears that future tremors could be catastrophic.
Potential for Future Megaquakes
Japan’s Earthquake Research Committee has projected a 70% chance of a magnitude 8-9 megaquake occurring along the Nankai Trough within the next 30 years. Such a quake could impact areas from central Shizuoka, about 150 kilometers south of Tokyo, to southwestern Miyazaki. The potential for tsunami waves reaching up to 98 feet within minutes of the earthquake further compounds the risk.
Impact and Economic Ramifications
A major earthquake in the Nankai Trough could affect roughly a third of Japan’s land area, home to about half of its 120 million inhabitants. According to a 2013 government report, the economic damage from such a disaster could exceed $1.50 trillion, more than a third of Japan’s annual GDP.
The Challenge of Earthquake Prediction
Despite the serious implications, predicting earthquakes remains elusive. Current scientific methods lack the capability to accurately forecast seismic events. An effective prediction would require a precursory signal from within the Earth that occurs consistently before major quakes—a technology that does not yet exist. As it stands, there is no reliable equipment to detect such precursors.
Japan’s proactive advisory aims to raise awareness and preparedness as the nation braces for the possibility of future seismic events in this volatile region.
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