Final answer:
The statement about strike-slip faults forming due to subducting plates in the Pacific Northwest, such as around Seattle, is false. The region's seismic activity is primarily due to the subduction of the Juan de Fuca plate beneath the North American plate, leading to volcanic activity, not strike-slip faulting like the San Andreas Fault in California.
Step-by-step explanation:
The initial statement regarding the formation of strike-slip faults in the Pacific Northwest due to the subducting plates is False. While strike-slip faults do exist in the region, such as the San Andreas Fault in California, the seismic activity in the Pacific Northwest, specifically around Seattle, is mainly associated with a subduction zone rather than strike-slip faulting. The major stress in this area comes from the Juan de Fuca plate subducting beneath the North American plate.
In the Pacific Northwest, the Cascade Range, which includes Mount St. Helens, was formed by the tectonic processes related to the subduction of the oceanic Juan de Fuca plate beneath the continental North American plate. This subduction process creates extensive volcanic activity, contributing to the formation of the mountain range. The stresses from the subducting plate do not typically result in surface rupture through strike-slip faults in this region.
The San Andreas Fault is a transform boundary between the Pacific and North American plates where the two plates slide past each other. Los Angeles, located on the Pacific plate, is moving northward. This fault structure is different from the compressive forces that generate the Cascade Range to the north.