Since the late 1980´s, the citizens of Oregon have become increasingly aware that their home is definitely earthquake country and that damaging earthquakes will strike the state. This growing awareness increased dramatically in 1993 when western Oregon experienced two damaging upper crustal earthquakes, Scotts Mills (magnitude 5.6) and Klamath Falls (magnitudes 5.9 and 6). The last significant earthquake in Oregon, prior to 1993, was in 1962. This earthquake shook the Portland area with a magnitude of 5.2. Next door in Washington, the Puget Sound area experienced even larger and more damaging intraplate earthquakes in 1949 and 1965 with magnitudes of 7.1 and 6.5, respectively.
In addition to earthquake activity in the historic record, prehistoric evidence for great subduction zone earthquakes and associated tsunamis has been found in coastal wetlands along the Pacific Northwest coast. The last one, approximately 300 years ago, may have been a magnitude 9 or greater, affecting coastlines from British Columbia to Northern California. What is most surprising is that evidence for this great earthquake also came from Japan. Japanese historic records indicate that a destructive distantly-produced tsunami struck their coast on January 26, 1700. It is very possible that the subduction zone earthquake, that produced this tsunami, occurred off the Pacific Northwest coast. Indian legends also lend some support to the timing of this last event.
A wealth of geological and seismological information on earthquakes in the Pacific Northwest is found on The
Oregon Department of Geology and Mineral Industries and the
U. of Washington Seismology Lab web sites. The sites include general information on the location and types of earthquakes, earthquake magnitudes and intensities, etc. Catalogs and location maps of recent PNW earthquakes, plus earthquake-related articles and hazard publications are also found on these sites.
For those of us who live in the Pacific Northwest, we can no longer be complacent about the potential risks that earthquakes pose to life and property. Therefore, it is imperative to prepare for the earthquake, especially before it happens. The
Federal Emergency Management Agency Mitigation and the U. of Washington Seismology Lab web sites offer much information on what to do before, during, and after the earthquake. By preparing for and mitigating hazards now, deaths, injuries and property damage will be greatly reduced and recovery from the earthquake will be much easier financially and socially and much faster.
If you have questions, or would like further information, please contact
Althea Rizzo, Geologic Hazards Program Coordinator.
