Answer :
Because unlike Pacific coast, East coast is not along the sides of tectonic plates.
The reason why there is intense geological activity in Washington and Oregon is
because both states are part of what is known as the "Pacific ring of fire." All
around the Pacific Basin there are not only volcanoes but also tsunamis and
earthquakes. The San Andreas fault is another example of such geological
activity in California. The study of plate tectonics applies here, and is
most interesting.