The Next Big Earthquake Could Sink Parts of the Pacific Northwest
Clip: Season 52 | 5m 8sVideo has Closed Captions
A massive earthquake along the Cascadia Subduction Zone could sink parts of the Pacific Northwest.
A 2025 study suggests that when the next "Big One" hits, coastal land could sink by up to 6 feet. That sudden drop could instantly double the number of people, homes, and roads exposed to flooding.
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The Next Big Earthquake Could Sink Parts of the Pacific Northwest
Clip: Season 52 | 5m 8sVideo has Closed Captions
A 2025 study suggests that when the next "Big One" hits, coastal land could sink by up to 6 feet. That sudden drop could instantly double the number of people, homes, and roads exposed to flooding.
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Learn Moreabout PBS online sponsorship- [Narrator] In this region, a massive earthquake is pretty much inevitable.
This is the Cascadia Subduction Zone.
It's one of the top hazards on the planet.
Here, the ocean floor is slowly diving under North America.
Massive earthquakes are expected here every 500 years or so, and the last one was in 1700.
- [Wendy Bohon] So it's not a matter of if, it's just a matter of when.
- [Narrator] A 2025 study suggests that the quake could suddenly sink part of the Pacific Northwest and climate driven sea level rise would only make it worse.
So why is the Cascadia Subduction Zone so dangerous and when will the next big one happen?
The Cascadia Subduction Zone is a major fault line that spans Vancouver Island in Canada to Northern California, but it's not really a line at all.
It's a crack where two massive tectonic plates meet.
It's where one of the largest earthquakes in the history of North America happened more than 325 years ago.
in January of 1700.
The earthquake had an estimated magnitude of nine, and it caused a tsunami.
A graveyard of trees that fell victim to flooding are still in the area.
The subduction zone has been pretty quiet ever since.
The last magnitude nine earthquake on Earth was caused by a subduction zone known as the Japan Trench in 2011.
It spurred a tsunami and caused widespread devastation, including a nuclear disaster at the Fukushima Daiichi power plant.
Subduction zones produce the biggest earthquakes in the world.
They happen where one tectonic plate is sliding down another plate.
- [Wendy] In Cascadia, you have one plate diving down beneath another.
This section gets locked and it pushes this part up.
When the fault ruptures, when the amount of stress overcomes the friction, it bounces back, which lifts up the water above it and causes that water to flow out in all directions.
And that water flowing out in all directions is the tsunami.
- [Narrator] The inevitable earthquake in the Pacific Northwest is what's called "the big one," and it would absolutely be devastating to a number of coastal communities.
But the Cascadia Subduction Zone is not actually one continuous fault line.
It has ruptures in it that form at least four major segments.
It's possible that an earthquake in one zone might not trigger an earthquake in the others, but the longer the segment, the bigger the quake.
One segment runs from Vancouver Island to the Oregon border.
Some scientists think that this is the most dangerous section and could spark the biggest earthquakes.
So when will this happen?
Unfortunately, earthquakes often happen without any clear warning signs, and scientists haven't yet identified reliable predictors.
The United States Geological Survey even says that, "Neither the USGS nor any other scientists have ever predicted a major earthquake," and that they do not expect to know how to predict earthquakes in the foreseeable future.
Whoa.
Even if scientists can't predict when an earthquake will strike, they can use analytical models to study the potential effects.
Some researchers found that if the Cascadia earthquake were to strike today, the coastline could suddenly sink by up to six feet raising the sea level.
And more than doubling the number of people, buildings, and roads currently exposed to coastal flooding risks.
Sea levels are already rising across the globe.
But the Pacific Northwest coast has seen much slower rise than other parts of the US coastline because of the subduction zone.
It's slowly pushing the coastline up almost as fast as the sea level is rising in some areas.
But a massive earthquake could quickly reverse that.
According to one projection, by the year 2100 sea levels along the Pacific Northwest could rise by almost three feet.
Combined with a Cascadia quake, that's a sea level difference of nearly nine feet compared to today.
And don't forget that when the earthquake strikes, it will trigger a tsunami, which could bring waves over 50 feet high in some locations.
For now, some communities are taking action against these deadly threats by creating high ground.
A tsunami could come only 15 minutes after an earthquake, and experts say it's imperative to get to high ground ASAP.
The thing is that in many low lying coastal communities, that isn't an option.
So vertical evacuation structures like towers and platforms where people can get to high ground without traveling, great distances are essential.
Right now, there are three vertical evacuation towers in the Pacific Northwest, a tsunami evacuation tower built by the Shoalwater Bay Indian Tribe, an elementary school gym that was rebuilt with a fortified foundation to withstand massive earthquakes and a new roof built to hold more than a thousand people, and an Oregon State University marine sciences building.
There are more vertical evacuation structures planned for the Pacific Northwest, but one study found that many more are needed.
The trouble is we don't know how much time we have until the next big one.
(pensive music) Thanks for sticking around.
Don't forget to subscribe to see more videos from Nova, and click the bell icon to make sure you don't miss anything.
See you again soon.
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