Pacific Northwest Earthquakes
This is the basic geology that contributes to earthquakes in the Northwest.
The Juan de Fuca Plate is being pulled to the east and under the North American Plate by currents in the earth's mantle.
The North American Plate is slowly creeping to the west.
This illustrates the basic movements of the Northwest crustal plates in relation to each other.
FAULT LINES are boundaries between two crustal plates.
The MAJORITY of the world's earthquakes occur on boundaries that slide past each other (strike slip), like California's San Andreas Fault, at the southern end of the Juan de Fuca Plate, and the Queen Charlotte Fault on its northern end.
On the other hand, the earth's LARGEST
earthquakes occur on subducting plates. The Juan de Fuca Plate is subducting – or diving under – the North American Plate.
The Pacific Northwest is unique in the lower 48 states because we have both types of earthquakes, the most frequent and the largest.