Cascadia Subduction Zone
According to the United States Geological Survey (USGS) the forces that produce earthquakes in western Oregon are generated as the Juan de Fuca oceanic plate moves northeastward with respect to the North American continental plate at an average rate of about 1.5 inches per year along the Pacific Northwest coast. At the zone of contact between the North America and Pacific Plates, the Juan de Fuca Plate slides beneath the North American continent and sinks slowly into the earth’s mantle, producing the Cascade volcanoes and earthquakes. The zone of the shallow, east-dipping subducting plate is called the Cascadia Megathrust Fault.
Studies have shown through geological evidence provided by buried soil layers, dead trees, and tsunami deposits that about every 500-600 years the upper portion of the shallow dipping Cascadia Fault ruptures offshore and releases this compression and causes great earthquakes of magnitude 8 to 9. (The information provided for this section was from a very fascinating read from the USGS entitled Earthquake Hazards and Lifelines in the Interstate 5 Urban Corridor.)
The consequence of a Subduction Zone earthquake are the largest earthquakes in the world, with a result of a minimum 8.5 magnitude quake. The last “big one” from the CSZ was in January 1700, the average times between quakes are less than 300 years apart. Needless to say, we are overdue.
We can expect numerous situations during and after a large-scale earthquake:
- The earthquake could last minutes, followed by equally large aftershocks and Tsunamis
- No power for at least a month
- Full scale utility service restoration (power, gas, water, sewer, communications, etc.) could take 3 to 12 months, if not longer.
- No clean water
- No access to sanitation
- Broken waterlines
- Fires due to leaking gas lines
- Damaged roads and bridges destroyed
- Thousands dead
- Tens of thousands injured
- Tens of thousands homeless
Reading this can seem bleak, but if we prepare and educate ourselves on how to live through and survive a “megathrust” quake, our chances of survival with multiply.
We have created an earthquake preparation page with guides and checklists on how you can prepare for yourself and your family during and after a major earthquake.
Additional websites with information regarding the earthquakes in the Northwest and the Cascadia Subduction Zone:
- Pacific Northwest Seismic Network, PNSN monitors earthquake and volcanic activity across the Pacific Northwest.
- Cascadia Region Earthquake Workgroup, CREW is a coalition of private and public representatives working together to improve the ability of Cascadia Region communities, businesses and homeowners to reduce the effects of earthquakes.
- OR Department of Geology and Mineral Industries, studies the vulnerabilities from earthquakes in Oregon.
- USGS, Pacific Northwest Geologic Mapping and Urban Hazards, using mapping studies to locate the major fault systems in the Northwest and determine their slip sense and history.