The western part of Washington State lies above the Cascadia subduction zone , where the Juan de Fuca Plate is being subducted beneath the North American Plate . The seismicity of this region consists of rare great megathrust earthquakes , like the 1700 Cascadia earthquake and more common earthquakes originating from within the subducting slab . These events relate to normal faulting , associated with the bending of the slab , possibly related to a phase change below about 40 km from basalt/gabbro to eclogite
1700 Cascadia earthquake
1700 Cascadia earthquake
1965 Puget Sound earthquake