Twelve earthquakes off the Oregon and Northern California
coasts were used in this research to study whether faulting associated
with these quakes was of the San Andreas type as observed in
California. The first motions of the incident P and S waves recorded
at various seismic stations in the Pacific Northwest were
used to obtain a fault plane solution for these earthquakes. Nine
earthquakes exhibited faulting which could be consistent with San
Andreas type of motion, where one of these motions was based on
first P and S data, six others were consistent with either northwesterly
right-lateral or northeasterly left-lateral motions, and
two were recorded at so few stations that faulting could not be defined
through a fault plane solution. One earthquake was located
in the region of the Gorda Escarpment west of Cape Mendocino,
California, and displacements appear to be associated with that
zone, one earthquake had Garlock-type displacements as defined
through P and S motions, and one earthquake was not associated
with any of the above types of faults.
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