The largest earthquake fault in Washington State is the Cascadia Subduction Zone (CSZ). It is located offshore, where the Juan de Fuca Plate is subducting beneath the North American Plate. The fault extends from northern California to southern British Columbia, and it can produce very large earthquakes, known as megathrust earthquakes.
The CSZ has the potential to generate earthquakes with magnitudes of up to 9.0 or higher, and these events can trigger massive tsunamis. The last major earthquake on this fault occurred in 1700, with an estimated magnitude of 9.0. Scientists believe the fault can produce such large events on a recurring cycle, with intervals ranging from 300 to 600 years.
Given the population density along the western part of Washington State, particularly around cities like Seattle and Tacoma, a major earthquake on the Cascadia Subduction Zone would devastate the immediate area and beyond.
An earthquake in Vanuatu could potentially trigger seismic activity on fault lines in Washington State. Still, the event would be highly unlikely to directly trigger a significant earthquake along the Cascadia Subduction Zone (CSZ) or other fault lines in Washington.