The Nankai Trough is a crucial geological feature located off Japan’s southwest coast, known for its potential to produce massive earthquakes. This underwater subduction zone, nearly 900 kilometers long, is where the Eurasian Plate collides with and forces the Philippine Sea Plate beneath it, leading to a buildup of tectonic stress. When this stress is released, it can cause a megaquake, an earthquake with a magnitude greater than 8.
Historically, the Nankai Trough has produced significant earthquakes approximately every 100 to 150 years. These events often occur in pairs, with the second quake typically happening within a few years of the first. The most recent pair of such earthquakes struck in 1944 and 1946.
In January 2022, Japan’s Earthquake Research Committee reported that there is a 70% chance of another magnitude 8-9 megaquake occurring along the Nankai Trough within the next 30 years. If this happens, it could generate powerful tsunamis with waves up to 98 feet high, impacting Japan’s Pacific coast within minutes.
The potential human and economic impact of such a disaster is immense. A 2013 government report indicated that a major Nankai Trough earthquake could affect about a third of Japan’s land area and nearly half of its population. The economic damage could exceed $1.5 trillion, which is more than a third of Japan’s annual GDP.
Despite these warnings, accurately predicting earthquakes remains impossible. Scientists would need to detect a specific signal from within the Earth that indicates a major quake is imminent. However, no current technology can reliably identify such precursors.
Following a 7.1-magnitude earthquake in southern Japan on August 8, 2024, the Japan Meteorological Agency issued its first-ever “megaquake advisory.” This advisory highlighted an increased likelihood of strong shaking and large tsunamis along the Nankai Trough, but it did not predict a specific earthquake. The advisory urged residents to prepare by reviewing evacuation routes and being vigilant for further warnings.
Japan’s Prime Minister, Fumio Kishida, canceled a planned trip to Central Asia to stay in the country and manage any potential crisis. The advisory does not mean a megaquake is certain to occur soon, but it serves as a reminder of the ever-present risk in one of the world’s most seismically active regions.
Historically, the Nankai Trough has produced devastating earthquakes, such as the 1707 event when all segments of the trough ruptured simultaneously, resulting in Japan’s second-most powerful recorded earthquake. Given the trough’s history and the uncertainty of when the next quake might occur, experts emphasize the need for preparedness without inciting panic. Even though the risk is elevated, it remains relatively low in the short term.
