Cascadia Subduction Zone

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

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.

(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.