The Cascadia Subduction Zone off the coast of North America spans from northern California to southern British Columbia. This subduction zone can produce earthquakes as large as magnitude 9 and corresponding tsunamis.
This shows Cascadia earthquake sources. (Image: USGS)
At the Cascadia subduction zone, the Juan de Fuca plate dives beneath North America (illustration: Oregon Department of Geology and Mineral Industries)
The area of the Cascadia subduction zone -- and the aftershock zone.
This image shows Cascadia margin turbidite (a current of rapidly moving, sediment-laden water) canyons, channels and 1999-2002 core locations. Major canyon/channel systems are outlined in blue. (Image: oregonstate.edu)
This is a seismic line. It shows "the sediment on top of the Juan de Fuca plate is scraped off and folded and faulted in what is called the “accretionary wedge”, which is essentially a wrinkled up rug of rock. That is what we can see best in these preliminary images, but the deeper subducting plate should be more visible out once the experts work their processing magic." (Image: PNSN)
Another rendering of the structure of the Cascadia subduction zone. (Image: USGS) Click here for more information.
This image of the Cascade Subduction Zone, shows the location of the trench, the downgoing slab, the active volcanoes and some major earthquakes. (Image: National park Service)
This shows what is going on in the subduction zone. "The Juan de Fuca plate, composed of dense oceanic crust and is covered in layers of sediment that has hardened into rock, is running into the North American plate," PNSN wrote on its blog. "Where they collide, the denser Juan de Fuca plate dives under (“subducts”) and the locked interface between the two is the Cascadia fault that breaks in magnitude 9-ish earthquakes every couple hundred years." (Image: PNSN)
This map shows the seismic lines PNSN shot overlain on the topography of the sea floor. "You can see the outline of Gray’s harbor and Long Beach Peninsula at right. to orient yourself. The black wiggly north-south-ish line at left indicates where the Juan de Fuca plate begins to subduct. The black lines show where we collected data to create 2D seismic images." (Image: NOAA)
A map, courtesy of the Washington State Seismic Hazards Catalog, shows expected shaking intensity in Washington. The New Yorker writes the cooler colors indicate lighter shaking, the warmer ones greater intensity. Photo via the New Yorker.
A new interest has sparked for some in the northwest, after the New Yorker's terrifying article on how the "big one" with the potential of a 8.7 to 9 magnitude will devastate Seattle and everything west of Interstate 5. In this slideshow, the Cascasdia Subduction Zone is explained in various images.
SEATTLE - The Cascadia Subduction Zone beneath the Northwest has the potential to cause the worst natural disaster in North American history.
Below is easy-to-understand information about the science behind the subduction zone and why people are talking about it now.
What’s the Cascadia Subduction Zone (CSZ)?
- A subduction zone is where two plates converge, and one plate is thrust beneath the other.
- A megathrust is when two crustal plates in a subduction zone collide.
The Cascadia Subduction Zone is a fault that sits along the bottom of the Pacific Ocean – stretching from Northern Vancouver Island to Northern California.
At the fault line: The Juan de Fuca plate is moving eastward underneath the North America plate at a rate of a few centimeters per year. Eventually, there could be a sudden slip at the fault line. This would create a megathrust earthquake.
What’s it capable of?
Earthquake experts say CSZ could cause the worst natural disaster in the history of North America, if it ruptures entirely. The CSZ has produced magnitude 9.0 or greater earthquakes in the past, and undoubtedly will in the future, according to PNSN.
The CSZ could deliver three to five minutes of shaking and a tsunami.
When did the last big one happen?
The last known megathrust earthquake in the Northwest was in January 1700.
The Cascadia Subduction Zone usually ruptures every 200 to 500 years, and we haven’t had one in 300 years.
What are the chances "the big one" will never come in our lifetime?
It’s impossible to predict when a monster quake occurs. But tectonic stresses have been accumulating in the CSZ for more than 300 years.
The area is more likely to have another deep source quake like the Nisqually, which occurred in 2001. Chances for another one are above 80 percent within the next 50 years, according to the PNSN.
Should I prepare?
Emergency management leaders encourage families to have a plan in the event of a disaster. People should prepare to survive on their own for seven to 10 days. Here's how to make an emergency kit on a budget.
Related headlines to the 'big one'
- SLIDESHOW: Geologic illustrations explain the Cascadia subduction
- How to build a 7-day disaster emergency survival kit on a budget
- State's largest quake drill ever to test readiness for ‘The Big One'
- Mexico's strongest earthquake in a century recorded at Mt. Rainier
- New simulations show how the 'big one' could play out in Seattle
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