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Earthquakes are a common phenomenon occurring somewhere on earth everyday (See: http://www.iris.edu/seismon//) Although infrequent in Oregon, our state has a history of earthquakes. (See PDF Map)
For example, the Scotts Mills (magnitude 5.6 on the Richter Scale) and the two earthquakes in Klamath Falls (magnitude 5.9 and 6.0) occurred in 1993 and caused extensive damage.
Based on geologic studies, Oregon is prone to great subduction zone earthquakes (magnitude 8 to 9). These earthquakes occur on average every 500 to 600 years, with time between such events ranging from as little as 150-200 years to as much as 800-1000 years.
The last great earthquake of a magnitude 9 or greater occurred in about 1700 AD. It shook the Pacific Northwest from British Columbia to northern California. Historically, though, Oregon experiences smaller earthquakes: such as the Scotts Mills and Klamath Falls earthquakes, more frequently.
Because of the state’s proximity to the Cascadia Subduction Zone, located just off the Pacific Coast, and to volcanic activity associated with the Cascade Mountains, it is important to be aware that there exists a chance you could experience a major earthquake while living in Oregon. If such a natural disaster occurs, how prepared will you be?
This section of the Department of Land Conservation and Development’s website will be expanded over time to help prepare Oregonians and their local governments to deal with earthquakes. Many local governments are the process of assessing their vulnerability to earthquakes through the development of a hazard mitigation plan that addresses the Federal Emergency Management Agency (FEMA) hazard mitigation planning guidelines.
The department has found several Internet links that will be useful in preparing for earthquakes and assessing your community’s vulnerability to earthquakes and other natural hazards. A greater awareness and understanding about earthquakes will make us better equipped to respond after an earthquake strikes.

Earthquakes: Helpful Resources
Damage to Molalla School via Scott Mills Earthquake in 1993