Scary Fact #2 – The Cascadia Earthquake

Posted: November 18, 2012 in Disasters and Geology, Scary Disaster Facts
Tags: , ,

Most people think California is THE BAD PLACE for earthquakes. I agree it’s pretty bad. After all, I grew up there (Northridge), shaking on a regular basis, and worrying about the big bad San Andreas earthquake that could happen at anytime. In fact, it was a relief to move to Oregon, where I wouldn’t have to worry about earthquakes anymore. NOT!!!!

A few years after we moved here in 1989, rumblings started about something called the Cascadia earthquake. The geologic news has worsened steadily since then. It turns out the Pacific Northwest is due anytime for one of the largest earthquakes in the world. Those of us who live here are gradually catching on, although it’s still a pretty big secret elsewhere. Even my daughter’s geology professor in Denver wasn’t really aware of it – sad!

The Cascadia subduction zone (a unique kind of fault) stretches from Mendocino in California to Vancouver Island in Canada – that’s 8oo miles long. It ruptures every 200-500 years, and we know the last one occurred on January 26, 1700 (~ 313 years ago). When the entire fault ruptures at once (sometimes only the southern half goes), it creates an earthquake lasting 4-5 minutes, magnitude of 9.0 or higher, involving everything from Mendocino to Vancouver, and extending inland to the Cascade mountains. It creates a tsunami 30-100 feet high that hits the entire coast within 15-30 minutes. The coastline drops 3-6 feet for good – goodbye beachfront! This will put it in the 5 largest earthquakes since 1900 (no one knows how large earthquakes were before 1900). Sounds very similar to the Japan earthquake of 2o11, except that our homegrown variety might cover a much larger area!

In human terms, the cities of Vancouver, Seattle, Portland, and Salem will all shake severely, with older buildings collapsing. The coast will be devastated by the tsunami, which will reach inland several miles. Most bridges along Interstate 5, our only major north-south highway, as well as most bridges over the Willamette River (which divides Portland and Salem in half) will be toast. Highway 1 along the coast will disappear, and landslides will close all the highways from the coast to the inland valley, leaving coastal towns completely isolated. They predict power out for weeks to months.

So if you live in the Pacific Northwest, the clock is ticking before we enter the history books. Good news: odds are that you will survive (unless you are on the coast). Bad news: life will be very, very different. Better start preparing now!

Stay safe,




  1. Deb says:

    Sheila, I was always intrigued by the cliffs alongside I-205 going through Oregon City. Perhaps they’re there from erosion by the Willamette, but they certainly look like they were pushed up by an earthquake. It’s sobering to think of what would happen if an earthquake took out the bridges. The Canby ferry, if it’s still in operation, might just be the only way to get across. Yikes!

    • disasterdoc says:

      I’m not sure about Oregon City area. I wonder if the Missoula floods caused the cliffs (luckily nothing to worry about until another ice age – definitely not the way the world is heading). I’m out of town, but now I’m curious, so I will check my resources when I get back!

      The bridges scare me terribly. Any bridge left standing, as well as boats, will probably be commandeered for emergency responders only.That’s why I push family plans and car emergency kits. If you’re on the opposite side of the river from your family when Cascadia hits, it may be days before you see each other (or home) again. Yikes!

      • disasterdoc says:

        Unfortunately, I was unable to find anything about the geology specific to the Oregon City cliff area. The whole Willamette Basin from Newberg north has a history of lava flows, severe erosion, smaller earthquakes, and the massive Missoula floods, but there wasn’t anything specific to Oregon City area. Any Oregon geologists out there with more information?

  2. […] of shaking, affecting coast and inland from Northern California to Vancouver Island (check out Scary Fact #2 – The Cascadia Earthquake to learn more about this terror). How do you prepare your house for something this big? The answer […]

  3. john says:


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