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What is the Cascadia Subduction Zone?

The Pacific Northwest coastline has a hidden danger just beneath the surface. Its name is Cascadia Subduction Zone.

The Cascadia Subduction Zone extends along the coast of the Pacific Northwest. Pictured here: Escola State Park, Oregon Coast
Escola State Park, Oregon Coast.

How dangerous is the Cascadia Subduction Zone?

The last massive earthquake from the Cascadia Subduction Zone was in the year 1700 and measured at 9.0 magnitude. There have been countless smaller quakes, but many of these are hardly noticeable for inland residents. History, however, has something to say about that. Cascadia earthquakes usually happen every 200 to 530 years, and we are in that timeframe now. As time passes, more pressure builds in this underwater megathrust fault.

It is impossible to determine precisely when this earthquake will happen. We do know the results would be catastrophic.  The Cascadia Subduction Zone is one of the world’s most dangerous fault lines. This fault line spans the coast of the Pacific Northwest, putting large cities like Seattle and Portland in its path.

We only need to look to the south to see how the modern-day Pacific Northwest would be impacted. Mexico was struck by two massive earthquakes this year. The first quake was the most powerful earthquake to hit Mexico in a century measuring 8.1 magnitude. The second was a 7.1 earthquake just two weeks later. The first shock sent tremors through Mexico City despite originating in the south. This second 7.1 magnitude quake, however, unleashed catastrophic damage upon this second-most-populated city of the Americas. Hundreds perished, tens of thousands of homes and businesses were leveled in a matter of minutes, and millions felt the tremors.

There’s one difference between the story of Mexico and the Pacific Northwest: tsunamis.

Residents in Oregon and Washington, especially in populated metropolises like Portland and Seattle, could see the same reality as the 2017 Mexico quakes. The difference is the added threat of a significant tsunami.

The amount of tsunami power hidden in the Cascadia Subduction Zone would spell trouble for the Pacific Northwest. A subduction zone is where a tectonic plate dives beneath another tectonic plate. The Cascadia zone is unique in its formation: sediments collect to form wedges, and these wedges are thicker than at most other subduction zones. These two-mile-thick wedges sitting on top of the fault are the reason that a rupture would reach shallower depths. While many subduction zones may go unnoticed, Cascadia is more likely to move the water above it with enough power behind it. The force wouldn’t be focused at a central point, but instead could ripple along the length of the zone parallel to the coastline. The power behind the Cascadia Subduction Zone grows every year.

The Cascadia Subduction Zone is to blame.
Sometimes the source of the problem isn’t so obvious.

If the Cascadia Subduction Zone ruptures, who will help?

Local and federal organizations won’t be able to provide immediate help after the “big one.” Organizations such as the Red Cross and the Oregon Office of Emergency Management admit it would take up to 2 weeks to assist after a Cascadia earthquake. That means residents of the affected area would be on their own for survival in the meantime.

When you consider your preparation plan, what are you missing? In this series, we will take you through what you need to survive for two weeks on your own. We will also give you tips on how to rebuild when the dust has settled. Where do you start? Check out this article that takes you through the basics when thinking about your preparedness plan.

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