The Cascadia Subduction Zone: Why the PNW is Boned

Hop on over here for a history of discovering this ticking timebomb.

What Will The Next One Look Like?

Buckle the fuck up.

As mentioned this fault is not like the San Andrea fault, with it’s two plates rubbing against each other in parallel. This is a subduction zone, where the Pacific plate is pushing the Juan de Fuca plate underneath the North American plate, but something, somewhere, has become stuck. That doesn’t stop the pushing, though. The North American plate over the Juan de Fuca plate is gradually becoming compressed at about an inch or two a year. Eventually, there will be enough built-up pressure to overcome the sticking point, and that land is going to decompress. Violently.

The Cascadia Subduction Zone has been calculated to be able to cause a Magnitude 9.2 earthquake. On the surface that doesn’t sound much worse than the 8.3 the San Andreas is capable of, but what you need to know is that earthquake magnitude is a logarithmic scale, which essentially means the worse things get, the faster they get worse. Intensity ramps up like a fight in the last two minutes of a Housewives episode and a 9.2 earthquake is roughly thirty times bigger than an 8.3. It makes The Big One look like The Manageable One. And research suggests there’s a one in ten to a one in three chance of it happening in the next fifty years.

So, let’s walk through a worst case scenario.

Your Name is Beezer

You’re a twenty-six year old sharing a house with your best friend Kyle. You love sharing a house with Kyle, but you also hate it and you’re only doing it because neither of you can afford a house on your own. It’s a two bed, two bath, with a sweet unfinished basement. In fact, that’s where the two of you are, having a jam out session.

The first thing that happens is your dog, Austin BowWowers, starts losing his mind. Barking, spinning around in circles, running around like he’s trying to find something. You don’t know it, because you and Kyle spent a week last summer putting up sound insulation to keep your stupid neighbor Mrs. Frances from complaining to the HOA again, but all the dogs in the neighborhood are having a Class Three Doggy Meltdown.

The plates have finally slipped, and sent something called a compressional wave along the ground. Humans can’t detect them, but dogs sure can, and while they don’t know what the fuck is about to happen, they do know they’re not supposed to hear them.

You don’t know any of this, because why would you? Austin BowWowers flips on you, you tell him to knock it off and toss a Milk Bone at him, and then forget about it. You never even connect it with the shaking that starts about ninety seconds later.

When it first goes off, you have no idea what it is. You’ve lived outside Portland your whole life and you’ve never experience an actual earthquake before. Your first thought is the boiler is about explode, and you take two steps toward the basement stairs before Kyle, who moved here from LA, tells you to calm down. Earthquake. Not even a big one.

Except then the shaking doesn’t stop. In fact, the shaking gets worse. And worse. Kyle stops giggling. This is more intense than everything he has ever experienced, and it just won’t end. The lights cut out. The house starts making weird groaning sounds and you swear the top half of the house is about to rock off the bottom.

It is. This is the first time you die. Nobody knew they needed to build earthquake proof buildings until, like, the nineties and since then they haven’t done a very good job of it.  Your house was built in the seventies, and when the earth pulls the foundation one way, the rest of the house stays put. And then falls in on you.

It’s the easiest way you’ll die today.

But Maybe You Weren’t in the Basement

Maybe you were out on the front porch smoking legal marijuana with Kyle. Now you hear the dogs barking but you still don’t know what the fuck is going on. Then the shaking starts. Kyle fills you in. At first, he tells you to stay near the house, but as the shaking continues and ramps up in intensity, the house behind you starts making some fucking weird noises. Kyle tells you to run into the yard. The two of you stand in the middle of your two hundred square foot patch of dead grass and hold on to the ground for dear life. The power cuts out, and transformers all around you explode in greens and purples. People are screaming. Your house collapses in on itself, as do the others on the block. They were all built at the same time, after all. The ground below starts to act more like a liquid instead of a solid and you want to run but where the hell would you even run to? The road splits behind you and Mrs. Frances Ford POS falls in. There’s an explosion. Then another. Gas lines all over the place are getting snapped in half, and it only takes a single spark.

Finally, after roughly six minutes, the shaking stops. Despite the intensity, despite the mayhem around you, the two of you are okay. The two of you start giggling because laughter is a valid emotional response to trauma and you are still high as balls. Kyle says you should stay put and see what shakes out – literally and figuratively. He’s used to earthquakes from the San Andreas Fault, after all, where the worst after-effects of an earthquake are aftershocks and fires. He says to stay, see if emergency services can come, see if there’s more shaking.

Within the next half hour you’re both dead, because there’s something about this earthquake that Kyle didn’t know was coming.

Tsunamis 101: Down, Up, Woosh

The Cascadia subduction zone is not a strike-slip fault like San Andreas. It is a subduction zone. A huge portion, hundreds of miles, of land directly under the ocean will be shoved down before rebounding back up a hundred or so feet away. The very basics of tsunami creation. One wave will be shoved out across the Pacific to inconvenience Japan in roughly ten hours. The other will have destroyed the coast of the Pacific Northwest in about thirty minutes.

The two of you are still carefully wandering around the neighborhood surveying the damage when the ocean shows up. Depending on where you are off the coast it will be anywhere from twenty to one hundred feet above your head and will be going about twelve miles an hour. Which doesn’t sound like a lot, but a fully grown man can get knocked on his ass in ankle high water going only six miles an hour. And think about the miles of land it had to get to you. You don’t live near the beach. Everything is mixed in with that water. Land and dirt from landslides. Entire cars. Hell, entire buildings. This is not something you can surf to safety. This is the end.

But Maybe You Knew It Was Coming

You and Kyle like to watch National Geographic a lot. You’d seen stuff on the potential for an earthquake here. As soon as the shaking stops you both know there is only thing to do: get Austin BowWowers in your Jeep Rubicon and drive east. Hell, you even pick up Mrs. Frances as she’s stumbling away from the ruins of her house and shove her in the back with Austin BowWowers before peeling out of the driveway and around the sinkhole that ate her car.

You know your goal: Interstate 5. Everything west of the interstate is going to be completely destroyed. You have to get east of the I5, and then keep going. Now that you’re in a car, the twelve miles an hour pace of the tsunami seems easy to beat.

Except this is the part where you die, like, three dozen times. Remember, everything has already been destroyed in the worst earthquake the continental United States has ever seen ever. You get stuck in traffic with others also trying to outrun the wave. You get caught behind huge tears in the ground even your precious Ruby can’t get across, or piles of rubble that used to be buildings that the Jeep just can’t get over. You have to know exactly where you’re going, and it has to work out perfectly.

Eventually, finally, you make it past the interstate. You just keep going. You’ve survived the Cascadia Megathrust earthquake and the tsunami that followed.

Oh, and One More Thing

You have an aunt living in the middle of nowhere in eastern Washington so you just keep driving. Thank Christ you filled up two days ago because the gas stations are all mob scenes. Very few people understand what happened and everyone’s panicking. You drive straight through and have to talk down your Aunt Sheryl because she tries to blow you away with her shotgun before you can even get the door open. You and Kyle and Mrs. Frances and Austin BowWowers pile in. She’s got a generator going, and you flip on the news because what the fuck else are you supposed to do?

They’re talking about it, of course. But there’s also about a one in four chance that’s not the only thing. Looking back through the records of the previous forty-one earthquakes, scientists discovered that that the Cascadia megathrust earthquake triggered the San Andreas fault eleven separate times. So, in one of these universe where you’ve made it to Aunt Sheryl’s, you’ve done so just in time to hear that the San Andreas has finally snapped. The Big One. There will be no other tsunami when the San Andreas goes. Just those fires that Kyle was so worked up about. Good thing out of control fires aren’t really an issue in southern California.

Aunt Sheryl goes into the basement to get the emergency moonshine and the five of you watch as the destruction of the entire American west coast unfolds in real time. At least until the generator runs out.


Sources

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