Nankai Trough

The Nankai Trough is a submarine subduction zone off southwestern Japan, where the Philippine Sea Plate descends beneath the Eurasian Plate and generates large earthquakes.

Nankai megathrust: The plate-boundary fault beneath the Nankai Trough, where accumulated strain can be released in large earthquakes. This fault is the source of the trough’s largest interplate earthquakes.
1707 Hōei earthquake: A magnitude 8.6 earthquake that ruptured much of the Nankai megathrust in 1707. It is the largest documented Nankai event and was followed by Mount Fuji’s 1707 eruption.
Nankai Trough earthquake: A large earthquake caused by rupture of the plate boundary beneath the Nankai Trough. This is the principal earthquake scenario considered in regional preparedness planning.
Nankai Trough earthquake prediction: Research and monitoring aimed at estimating the timing or likelihood of future Nankai Trough earthquakes. The recurrence record supports hazard estimates but cannot specify an earthquake’s date.
Nankai Trough megaquake: A hypothesized future great earthquake involving a substantial portion of the Nankai subduction zone. This scenario underlies Japan’s estimates of potentially widespread damage and casualties.
Philippine Sea Plate: A tectonic plate moving northwest beneath southwestern Japan and neighboring regions. Its convergence drives subduction along the trough.
1854 Ansei-Tōkai earthquake: A major 1854 earthquake that ruptured the eastern part of the Nankai subduction zone. Its rupture preceded the Ansei-Nankai earthquake by about 32 hours.
Japan Meteorological Agency: Japan’s national agency for weather, earthquake, tsunami, and volcanic monitoring and warnings. It issues information and warnings relevant to Nankai seismic activity.
Earthquake recurrence interval: The time between successive earthquakes on a fault or fault segment. Nankai intervals vary, complicating forecasts based on elapsed time alone.
Shikoku: The smallest of Japan’s four main islands, situated beside the western Nankai Trough. Its Pacific-facing coasts are exposed to strong shaking and tsunami inundation.

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