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Pacific Northwest Earthquakes
Figure 11.
Cross sections of Washington showing plate convergence (top fig
ure) and earthquake
hypocenter locations. Some major topographic features and underl
ying geologic structures of
Washington are shown diagrammatically in the upper figure. In th
e lower figure, selected hypocenters of
earthquakes that occurred in 1982 through 1986 between latitudes
47' and 48'N are projected onto a vertical plane that generally
corresponds to the diagram in the upper figure. Because of the
great number of
shallow earthquakes that occurred between 1982 and 1986, only hy
pocenters of those having magnitudes
equal to or greater than 1.8 are shown in the lower figure. Belo
w 30 km, hypocenters of all earthquakes
having magnitudes of 1.0 or greater that occurred during this pe
riod are shown. The distribution of deep
earthquakes indicates the slope of the zone of subduction. In th
e lower figure there is a vertical exaggeration of 2 to I below
sea level; this creates the illusion that the subducting Juan de
Fuca plate dips more
steeply than it actually does. Topography indicated on the lower
figure has a vertical exaggeration of 12
to 1.
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