Question

michael
what tectonic plates were involved in the 1700 cascadia earthquake?
observe new image on the right
the nazca plate subducting under the north american plate
the juan de fuca plate subducting under the north american plate.
the pacific plate subducting under the north american plate
the nazca plate subducting under the south american plate

Explanation:

The 1700 Cascadia earthquake was a result of the Juan de Fuca Plate subducting under the North - American Plate. This is evident from the image and information provided.

Answer:

The Juan de Fuca Plate subducting under the North American Plate.