Pacific Northwest: Three types of tectonic earthquakes

4min 13s Novice

Subduction-zone earthquakes aren't the only ones...

The Pacific Northwest is host to more than the anticipated megathrust earthquake that will happen off the Cascadia coast in the future. That earthquake will be due to the stress building between the Juan de Fuca and North American plates as the oceanic Juan de Fuca plate dives deep beneath the Pacific Northwest. However, there are also deep earthquakes within the subducting plate, and shallow earthquakes in the overlying continental crust. This is because of additional forces acting on the region besides subduction-zone processes.

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The Pacific Northwest is host to three kinds of tectonic earthquakes :

  • Magnitude nine Cascadia megathrust quakes
  • Magnitude 6.5­ to seven deep earthquakes , and
  • Shallow crustal-fault earthquakes with magnitudes up to 7.5.

Related Animations

Subduction zones show that there are 3 distinct areas of movement in the overlying plate:

  1. constant movement above the locked leading edge,
  2. see-saw pattern of back-&-forth movement above a zone that alternately locks then slips, and
  3. no movement far inland above the deeper part of the diving oceanic plate.
Animation Novice

This UNAVCO animation compares Japan's subduction zone at the location of the 2011 earthquake with a mirror-image subduction zone in the Pacific Northwest. There are many similarities.

Animation Novice

Ghost forests are part of the evidence that a Great earthquake and devastating tsunami occurred last on January 26th, 1700 in the Pacific Northwest. How do we know this?

Animation Novice

The Pacific Northwest boasts an active volcanic arc (Cascades), a nearby ocean ridge (between Pacific & Juan de Fuca Plates), the world’s youngest flood basalt province (Columbia River Basalt), a hot-spot chain of eastward-younging volcanoes (Yellowstone), Basin-Range extension, and more. This animation simplifies several complex tectonic interaction. 

Animation Intermediate

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