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Nankai Trough

Context

Japan has issued its first-ever advisory on the heightened risk of a "megaquake" following a strong magnitude 7.1 earthquake along the Pacific coast’s Nankai Trough. This advisory highlights the potential for a much larger and more destructive earthquake in the near future.

What is the Nankai Trough?

  • Nankai Trough is a seismic zone off Japan's southwest Pacific coast, extending approximately 900 km (600 miles).
  • It is where the Philippine Sea Plate is subducting beneath the Eurasian Plate, leading to significant tectonic strain.
  • Simply put, it is an underwater subduction zone where the Eurasian Plate collides with the Philippine Sea Plate, forcing the latter under the former and into the Earth’s mantle. 
  • Megaquakes in the Nankai Trough are expected roughly once every 100 to 150 years.

Key-Concepts

  • Megaquake: The term "megaquake" refers to exceptionally large earthquakes, often with magnitudes of eight or higher. Historical examples include the 1707 quake, the eruption of Mount Fuji in 1854, and subsequent significant quakes in 1944 and 1946.
  • Subduction Zone: A subduction zone is a collision between two of Earth's tectonic plates, where one plate sinks into the mantle underneath the other plate. Subduction zone faults build stress, and a so-called megathrust earthquake takes place when a locked fault slips and releases that stress. “Megaquake” is a shortened version of the name.

 

    • Subduction zones occur in a horseshoe shape around the edge of the Pacific Ocean, offshore of Washington state, Canada, Alaska, Russia, Japan and Indonesia and down to New Zealand and the southern edge of South America
    • Called the "Ring of Fire," these subduction zones comprise “the most seismically and volcanically active zone in the world. The Pacific “Ring of Fire” is a collection of subduction zones.
      • In the U.S., the Cascadia subduction zone off the West Coast runs from Vancouver Island, Canada, to Cape Mendocino, California. 

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