Shallow Crustal Quakes in Washington and Oregon
Shallow (depth less than 25 km) earthquakes with magnitudes up to 7.5 may occur in Washington and Oregon. This type of earthquake occurs within the North American continental crust.
A schematic diagram shows the relative postions of the
Juan de Fuca and North American Plates. The blue dots show the positions of known large crustal earthquakes in map view and cross-section. These earthquakes include two on Vancouver Island (M 7.3 in 1946 and M 7.0 in 1918), the M 6.8-7.4 North Cascades Earthquake in 1872, and an earthquake on the Seattle Fault 1,100 years ago.
Largest Known Crustal Earthquakes in Washington, Oregon, and British Columbia
There are many sources of shallow crustal activity, but which faults are large enough to be a serious hazard is not well understood. Possible sources with recent geologic activity are under investigation.
Earthquakes losses from all types of faults can be decreased
through mitigation, retrofitting, good building standards, and planning.