[hoagy62]

If the Cascadia let’s go, I doubt any of the Cascade volcanoes would erupt.
Granted, Seattle, Portland, and a bunch of other places would be wrecked, but I doubt there would be any eruptions.

[Bonemaker]

Does it reach as far as Yellowstone?

[Max in Utah]

Interested in West Coast earthquakes? Here is a great video:

Great Earthquakes of the Pacific Northwest

CWU's Nick Zentner presents 'Great Earthquakes of the Pacific Northweset' - the 13th talk in his ongoing Downtown Geology Lecture Series. Recorded at Hal Holmes Center on February 10, 2016 in Ellensburg, Washington, USA.

Great Earthquakes of the Pacific Northwest

[Alas Babylon!]

I don’t know about that. The Juan de Fuca Plate is subducting under the North American Plate. That is what formed the Cascades themselves, and Mt. Baker, Rainier, St Helens, Hood, Shasta are all fed by the magma that has escaped up from the melting crust in the mantle.

The water being brought in from the Juan de Fuca Plate also has a huge impact on those volcanoes. More water, more pressure going up those magma channels.

A massive slip on the subduction area could pop those channels wide open.

Probably not all at once, but the one closest to the big slip.