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.