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The Cascadia Subduction Zone - What is it? How big are the quakes? How Often?
WHAT IS THE CASCADIA SUBDUCTION ZONE?
The Cascadia Subduction Zone is a very long sloping fault that stretches from mid-Vancouver Island to Northern California. It separates the Juan de Fuca and North America plates. New ocean floor is being created offshore of Washington and Oregon. As more material wells up along the ocean ridge, the ocean floor is pushed toward and beneath the continent. The Cascadia Subduction Zone is where the two plates meet.
The width of the Cascadia Subduction Zone fault varies along its length, depending on
the temperature of the subducted oceanic slab, which heats up as it is pushed deeper beneath the
continent. As it becomes hotter and more molten it eventually loses the ability to store mechanical stress and generate earthquakes.
The "locked" zone is storing up energy for an earthquake, and the "transition" zone, although
somewhat plastic, could probably rupture.
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HOW BIG ARE CASCADIA SUBDUCTION ZONE QUAKES?
Great Subduction Zone earthquakes
are the largest earthquakes in the world, and can exceed magnitude 9.0. Earthquake size is porportional to fault area, and the Cascadia Subduction Zone is a very long sloping fault that stretches from mid-Vancouver Island to Northern California. It separates the Juan de Fuca and North
America plates.
Because of the very large fault area, the Cascadia Subduction Zone could produce a very large earthqauke, magnitude 9.0 or greater, if rupture occurred over its whole area.
HOW OFTEN ARE CASCADIA SUBDUCTION ZONE QUAKES?
The last known great earthquake in the northwest was in January, 1700,
just over 300 years ago.
Geological evidence indicates that great earthquakes may have occurred at least
seven times in the last 3,500 years, suggesting a return time of 400 to 600 years.
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