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  • Context (NDTV): A recent study warns that major US cities are at risk of catastrophic quakes due to the Cascadia Subduction Zone.

Cascadia subduction zone - PMF IAS 

Credit: Researchgate

  • The Cascadia Subduction Zone (CSZ) “megathrust” fault is a 1,000 km long dipping fault that stretches from Northern Vancouver Island to Cape Mendocino California. It separates the Juan de Fuca and North America plates.
  • It is an active convergent boundary where the Pacific Ocean floor is subducting under North America. – and when the fault periodically locks and releases, it can unleash devastating megathrust earthquakes and record-breaking waves.

A schematic cross section of the Cascadia Subduction Zone - PMF IAS

(Left) A schematic cross section of the Cascadia Subduction Zone shows the ocean floor plate (light grey) moving under the North American continental plate.

  • The fault zone is not a continuous structure but is divided into at least four segments and is divided by buried features, including big faults.
  • Causes of the segmentation: Differing composition of rocks at the rigid edge of the overriding North American continental plate as they are formed at different times, with some being denser than others.
    • This causes the incoming, more pliable oceanic plate to bend and twist to accommodate differences in overlying pressure.
  • Megathrust fault is a place where tectonic plates move against each other in a highly destructive manner. Such a fault off Japan caused the 2011 Fukushima nuclear disaster.
  • Megathrust earthquakes are the most powerful on Earth, and they arise from subduction zones.

Learn in detail about Ocean-Continent submergence.

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