Geology Reference
In-Depth Information
The Corvallis fault, up-thrown on its northern side, passes diagonally between Corvallis and a low
range of hills (Vineyard Mtn.) (photo by Western Ways of Corvallis).
pinpointed in time nor evaluated with respect to their
magnitude. A catalog kept at Oregon State University
lists a total of 1,286 known seismic occurrences from
1841 to 1986 in Oregon and southern Washington. Of
these, approximately 440 earthquakes were associated
with the eruption of Mount St. Helens in 1980, and
250 occurred before 1962 when records were first kept
by modern instruments. The seven largest earthquakes
in Oregon during this period began with the November
23, 1873, shaking of Port Orford and Crescent City at
an estimated magnitude of 6.3 on the Richter scale.
The outward limit of this shock was felt from Portland
to San Francisco. Of the Oregon cities, Port Orford
suffered the most with damage to chimneys. Other
powerful tremors shook Portland in 1877, Umatilla in
1893, Richland, Washington, in 1916, Milton-Freewater
in 1936, Sauvie Island in 1964, and the Adel-Warner
lakes area in 1968.
