The Cascadia Subduction Zone: The PNW Has Been Boned

The Big One

In case you missed that day in sixth grade science class when your teacher played the earthquakes episode of Bill Nye the Science Guy because he was hungover and wanted to sit in the dark while he nursed an oversized coffee mug full of Pedialyte and questioned his life choices, the crust of the earth is broken up into tectonic plates typically the size of continents and oceans.

Pictured: God surveys His mistakes, circa 1998.

These plates are floating around on molten lava, so they’re constantly jostling each other. Because the plates are made up of a bunch of broken geology mashed together, these plates often get stuck as they try to move. Pressure builds until it’s finally enough to get past the sticking point, and then the Rock shows up to punch the earth back into submission. Or something. I did watch that movie, but only as background while I played around on my phone.

Fault lines are where those plates meet, and the most famous is probably the San Andreas Fault (I’m assuming, anyway. I can’t name another fault, besides the one we’re about to talk about. If you can name another fault, please email me at It runs through most of California, but it’s the southern portion that will someday produce (overly dramatic drum roll)…The Big One. The northern section produced the San Francisco earthquake in 1906, and the central section the 1857 Fort Tejon earthquake, but the southern section has been without a major earthquake for over three hundred years. Three centuries of pressure building like a forgotten beer in the freezer. This is something scientists generally refer to as ‘A Bad Thing’ and officially refer to as ‘Oh Shit, Oh Fuck, We Are So Fucking Fucked’ (see also: climate change).

There is some relatively good news. Due to the depth of the Fault and the way it’s stuck, scientists believe that it could only ever reach an 8.2 on the Richter scale and is currently primed for a 7. Because it’s almost entirely on land and, again, because of the way it will move there’s almost no chance of it causing a tsunami. Most importantly, because the Fault produces regular earthquakes of the non-city-destroying size, everyone who lives in southern and central California know that earthquakes are part of the package. No one in the San Fernando Valley is getting rocked awake at two in the morning by a 4 and thinking to themselves, ‘This wasn’t part of the advertised packaged!’ Everyone knows the Big One is coming sooner or later, and that knowledge means that a lot of people and local governments are more or less prepared.

Golly, could you imagine living on top of a massive fault line your entire life and never even knowing?

Cold Coals in the Ring of Fire

The Ring of Fire is a colloquial term given to just about every coast that touches the Pacific Ocean. Starting in New Zealand, you can trace it all the way up through the islands of the western pacific and the east coasts of Asia including all of Japan, until it crosses the northern ocean to meet Alaska and then covers the entirety of the Americas’ west coasts. Unlike a lot of other science terms, the Ring of Fire is exactly as dramatic as it sounds, describing places where shifts in tectonic plates make earthquakes and active volcanos pop off at semi-regular to constant intervals. Japan is shook by minor tremors on a close-enough-to-daily basis, and the earth tries to toss Chile into the ocean every sixty-ish years or so.

Only, there was a gap. The Pacific Northwest of the United States, specifically Washington and Oregon, wasn’t known for having major earthquakes despite being dead squat center of Earthquake Alley. There have been some, of course, but comparing the amount of earthquakes recorded in Oregon or Washington to the amount in California or Alaska is like comparing the amount of sexual partners of the average male to Wilt Chamberlain. Back before plate tectonics were understood, scientists were probably all, “I don’t know, I guess the ground ghosts don’t like to do haunts here,” but eventually scientists realized a lack of ghosts was the least of their problems.

 They figured out the next part through logic. The San Andreas Fault, with its two plates grinding against each other in parallel, is actually an outlier. Most of the plate movement around the Ring of Fire is subduction, where one plate is diving under another. In the Pacific Northwest, scientists discovered that the relatively tiny Juan de Fuca Plate is being shoved under the North American Plate by the slowly encroaching Pacific Plate. The eastern end of the Plate was melting and forming the Cascade volcanoes (including Mount St. Helens, which famously exploded sideways in 1980). The western end, near the coast, should have been setting off earthquakes as regularly as every other subduction zone along the Pacific.

It just wasn’t. There were two possibilities here: the fault was stable enough that it never produced earthquakes, at least not big enough ones to be noticed. Or the area went through cycles of stability broken up by literally earth-shattering events, and the Pacific Northwest had been in one of those stable periods the entire time white people had been there.

You can guess which one made them shit their pants.

The Ghost Forests of Washington and Oregon

I know what you’re thinking, and you can stop packing your ghost hunting shit right this second. Ghost forests are not called that because the trees are infested with ghosts, and you are not mere days away from starting your own ghost hunting and befriending adventure. Your time is soon, buddy, but not today.

No, in a ghost forest the forest is the ghost. Broken stumps jut out from unforgiving sand and surf as though pointing a finger at the sky in indignation. In the Pacific Northwest, these dead forests can be made of old spruce and cedars, and are found along the coastline. Some of these ghost forests are thousands of years old and are simply the result of time marching on. Land changes, ocean waters rush in, the trees are like, ‘I fucking hate salt,’ and they die.

Some of these ghost forests, though, are much younger. And there was something else odd about them, too. In the late 80’s a geologist named Brian Atwater was at one of these ghost forests in Washington and, being a geologist, followed his basic nature and started digging. Instead of finding evidence of a gradual death, he found the exact opposite: a layer of local grass that had been preserved under the sand, indicating that the forest he was standing in had died in a matter of a minutes. These trees hadn’t been slowly smothered to death by encroaching ocean waves. The land they had all been chilling on had, seemingly out of nowhere, dropped an entire five feet, effectively dunking the trees and their roots directly into the ocean. Imagine what would happen to your self esteem if the literal ground beneath you went, ‘You know what, fuck you lmao’ and fucking destroyed itself to also destroy you. You wouldn’t make eye contact with anyone for a month.

Because Atwater was an actual scientist and not that ‘ancient aliens’ meme guy, he understood that the only thing that could have caused that sort of damage was an earthquake followed by a tsunami and not, you know, ancient aliens (real quick fun fact: ancient aliens aren’t real and ancient alien theories are thinly veiled racism. It’s just a white dude saying, ‘It’s literally easier for me to believe that a bunch of intergalactic travelers came here for the express purpose of building a smattering of pyramid shaped buildings for unknown reasons than to admit brown people are capable of construction.’). In fact, with help of another scientist, David Yamaguchi, they were able to determine that the forest’s death wasn’t even ancient! Because trees are insanely good timekeepers (seriously, if you are even three minutes late to a tree party they will all judge you harshly long after your dead corpse has become fertilizer for their roots) they were able to pinpoint a ten month period that this possible earthquake happened: August 1699 and May 1700.

Unfortunately there are no records from that time period. Barring some lucky break, it seemed the investigation into the missing earthquakes was at an end.

Some Lucky Break: The Orphan Wave

If an earthquake had happened, and if said earthquake had shifted the face of the earth enough to kill a bunch of forests, than surely the tsunami it set off would have been massive and far-reaching. Hey, where does the word tsunami come from, anyway?

So, someone gets the idea to go searching through Japan’s records. Japan’s history with earthquakes and tsunamis is long and exhausting, and they have detailed records of close to every single one going all the way back to about 599. Various towns and prefectures had kept their own records going back centuries, and these records were collected into a single catalogue in 1899. It was through this thorough record keeping that researchers learned about the Orphan Wave.

Every tsunami in the records had come after an earthquake, except one (probably. I’m not doing a deep dive here. What I’ve looked through implies that there wasn’t any other incidence of a tsunami without an earthquake, but I did not personally go through all of the records myself). This one had seemingly gotten all liquored up and decided to start a good time on its own, crashing the party without ever being invited. The villages that the waves overran were all asleep when they showed up, because there hadn’t even been a tremor to warn them it was coming. We now know how far and how fast tsunamis can travel and still be deadly, but at the time it must have been a terrifying development. The leaders of one village referred to the wave in their record as the Orphan Wave because it had no earthquake parents.

You can already guess when the Orphan Wave struck and what it was caused by. The interesting thing is, the record of this lone tsunami is so meticulous we know precisely when it struck: midnight Japan time, January 26, 1700. A seismologist named Kenji Satake finally put all the pieces together in a 1996 article: A massive 9.0 earthquake rocked the Pacific Northwest at around 9 pm on January 26, 1700, then sent a tsunami to go wake up Japan. This was what scientists were looking for. Further research has discovered that the area experienced a cataclysmic earthquake forty-one times in the past ten thousand years, a rough average of one every two-hundred and forty-three years.

How Fucking Cool Is That?

Before moving on, I really want to make sure we’re all appreciating how cool this entire scenario is. Why hasn’t somebody made this movie yet? In the span of about thirty years, we went from ‘this area doesn’t have earthquakes,’ to ‘wait, this area should have earthquakes’ to ‘oh, Christ, this area has bad earthquakes we’ve just been lucky and that luck is going to run out,’ and we got there with the help of a bunch of dead trees, a tsunami on the other side of the world, and a whole lot of science. I keep saying ‘scientists’ not to be vague but because there were a whole lot of disciplines involved. Within half a lifetime science was able to solve a mystery we didn’t even know we had.

Thunderbird and Whale

There are no written records from the Pacific Northwest around 1700, but not because there weren’t any people. The people who lived there kept their history in an oral tradition. One of their stories is about Thunderbird and Whale.

There are a lot of variations, as there usually are in oral storytelling, but the basics are often the same. Thunderbird and Whale have a fight. Sometimes Thunderbird is the bad guy, other times Whale fucked around and found out. What is strikingly similar, in each telling of the story, are the effects of the fight. The earth bucks or trembles as Thunderbird slams Whale into the ground, and great waves come in from the ocean and wash away land, trees, animals and people as Thunderbird drags Whale through the ocean.

There were also a lot of stories floating around from great and great-great grandparents that generally dated to the time of the earthquake that just…describes the earthquake and the landslides and the tsunami.

It took the people involved in solving the mystery of this 1700 earthquake an embarrassingly, but not surprisingly, long time to think of asking the native peoples if they had any sort of record of it. By the time they did, it only served to support their theories. As always, maybe if white settlers had actually listened to the people who knew the land they had been living on for generations, we might have been able to avert disaster.

Two Hundred and Forty-Three Years Ago

Eagle-eyed and calendar owning viewers may have noticed something fun in this article! The average time between earthquakes is less than two hundred and fifty years, and 1700 was over three hundred years! Now, of course averages are not strict schedules, but scientists have a term for this sort of differential.

Fucking. Yikes.

We’ll talk about what that means for the Pacific Northwest right here.


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