- The Cascadia Megaquake will likely be the biggest disaster to ever hit the United States.

But new research now shows that it could be way worse than we once thought.

- There will be, you know, likely very large fuel spills, which are generally accompanied by fires.

- It may also create a toxic cloud.

- A power outage for six to 12 months.

- The last megaquake happened at 9:00 PM January 26th, 1700.

Scientists were able to pinpoint this exact moment in part because of Japanese record keeping detailing a mysterious orphan tsunami that hit coastal villages without warning.

This was 325 years ago.

But this is bad news because it means we're due for another one and we're not prepared.

Scientists predict a dire scenario when the next one hits.

Buildings will crumble.

Bridges and overpasses will collapse.

Critical infrastructure along our rivers and coasts will sink and spill.

Oh, and a tsunami up to 100 feet tall will overwhelm our coastal towns and cities.

But new research is providing a much more complete picture of what will happen after the shaking stops, and it might be even worse than the shaking itself.

- I stayed up many nights when I was writing this report out of fear.

So the whole thing is, you know, an environmental and economic kind of catastrophe waiting to happen - And stay tuned because although this new research is scary, we're going to go through some ways to keep yourself safe when the big one hits, and it's not what you might think.

In modern times, earthquakes are the most deadly natural hazard.

They hit suddenly, without warning, and their death tolls can be staggering.

Globally, the most deadly earthquakes have occurred in Asia.

The US has been spared from those horrifying death tolls.

The San Francisco earthquake of 1906 was the deadliest in the US claiming 3000 lives, mostly from the fire that followed.

But the West Coast is due for a much bigger quake, the largest one, the US as we know it, has ever seen.

And it has a unique quality that makes it especially deadly.

- The Cascadia Subduction Zone is a fault that is offshore of the Pacific Northwest.

It's about 700 miles long, and it's a place where two tectonic plates are colliding.

And one, the Juan de Fuca plate is diving beneath the North American plate.

And right now those two plates are locked against each other.

They're accumulating strain and sort of gathering up energy to release in the next earthquake.

But the unique thing about the subduction zone is that it's very seismically quiet.

- The Cascadia Subduction Zone is a relatively recent discovery.

Of course, native communities along the West Coast knew about it, but scientists didn't start piecing together the mystery until the eighties.

And by that time, whole cities, towns, and infrastructure were built all with no earthquake standards.

- We have a lot of very old infrastructure.

Buildings that are a hundred or more years old.

They were built decades before plate tectonics was even known.

- So we've built on low lying areas that are very sensitive to tsunami inundation and land level change.

- But while the subduction zone may be quiet on a year to year timescale, it's anything but inactive.

There have been over 40 major earthquakes along the fault over the last 10,000 years, and in the last 7,000 years, around 10 of those quakes were big ones.

Over 8.5.

Today, scientists estimate that we have a one in three chance of a quake hitting in the next 50 years, and around a 15% chance of a really big one.

And it could rival the 2011 disaster in Tohoku, Japan.

One of the most expensive natural disasters in history.

But there is one critical difference.

They were prepared.

We are not.

- In the Pacific Northwest, we're, you know, roughly a thousand years behind Japan in our preparedness.

- There's new research that the impact to our unprepared cities could be much scarier than we once thought.

We'll get into that in a bit, but first, let's talk about the major impacts that we've known about for years.

First, the shaking.

- Those kind of earthquakes generate heavy shaking.

Of course, the coastal areas will feel that as ridiculously strong shaking, probably exceeding one G, which is enough to lift cars and people off the ground.

And it'll go on for three to six minutes.

It seems endless.

- The major cities get a bit of a break with less severe shaking than the coast because they are slightly inland from the fault.

But there are a lot more people living in cities and a lot more vulnerable buildings and infrastructure.

- Bridges, water systems, electrical systems, natural gas systems, fuel systems, other transportation like rail and port and airports.

Most of these have not been designed specifically to tolerate shaking.

We would expect to have an electrical blackout for the entire impacted area.

- And then there's the tsunami.

- There'll be a tsunami launched from the offshore, and the delay time for that could be as low as 10 to 15 minutes for people who live just right adjacent to the earthquake.

- We covered the tsunami and how to stay safe in a past episode of Weathered.

If you live in a coastal area or vacation there often be sure to watch it.

Tsunamis are often the deadliest part of an earthquake.

- Over 30,000 casualties are expected in such an event and totaling over $81 billion of damage.

So the costliest natural disaster basically to ever affect the United States.

- The costliest natural disaster in US history, how could it be any worse than that?

Along the banks of the Willamette river in Oregon, just a couple miles from downtown Portland sits the critical energy infrastructure hub.

90% of Oregon's fuel comes through the hub to be distributed throughout the state.

- These huge storage tanks full of everything from jet fuel to car gasoline to diesel to lubricants and things like that, sitting on the banks of the Willamette River.

- A lot of these large petroleum tanks that are located right along the Willamette River were built to insufficient seismic codes.

You know, many of them were built pre 1970.

- We've known this site poses a great threat during a megaquake for years, but Luke's research revealed a terrifying new detail.

- There are other hazardous materials besides petroleum products in the CEI hub and in the industrial areas.

It became very clear early on that there is information that is missing.

- But first, we need to understand what makes these tanks so unsafe in the first place.

And it has to do with the process called liquefaction.

- Liquefaction is where you have loose sandy soils that when you shake that sandy soil temporarily turns into a liquid.

And so a liquid cannot sustain anything built in it or on it.

So if it's a building, it could get torn apart.

If it's something buried like a pipeline or tank, it could pop up out of the ground.

- Soils along rivers and waterways are especially vulnerable to liquefaction, and that's where we built a lot of our critical infrastructure and hazardous material storage.

- So along with the shaking that is gonna cause sloshing inside of these large fuel tanks that shaking can directly damage the tanks.

This liquefaction in these forms of ground failure can exacerbate the seismic hazard and cause greater damage at these large fuel facilities.

Something like 50% of the material could be spilled.

It would be equivalent to the deep water horizon spill, which took place over months, and it would happen like that.

That could flow into the river and make it to the coast and light on fire and potentially affect Forest Park right there on the hills.

- With the right conditions a fire could spread rapidly in Portland's 5,200 acre urban forest and could threaten 70,000 people in the aftermath of a megaquake.

The resources typically available to stop a wildfire just won't be there, and the results could be catastrophic.

But it doesn't stop there.

When these tanks fail, they would emit toxic plumes that could wat over parts of Portland and could be deadly.

- So these are things like anhydrous ammonia or chlorine gas, a huge array of chemicals that can become a toxic inhalation hazard.

- The report focused on just four of the highest risk facilities and created different scenarios based on the most likely wind patterns.

The deadliest weather conditions could be in the summer when air is stagnant and the gases could linger.

More than 2,500 people could die from toxic gas exposure and hundreds of thousands could be affected.

- The people of the Linton neighborhood and people living up in the hills of Forest Park are in an incredibly dangerous position.

The evacuation challenges are going to be really fierce.

One of the most risky places in Oregon.

- The team modeled just four industrial facilities in North Portland, but identified 70 high risk sites mostly on liquefiable soil.

And that's only around Portland.

Similar risks can be found all throughout the Pacific Northwest.

Okay, so toxic gas clouds, fires in the hills, buildings and bridges collapsed.

It all sounds truly apocalyptic, but that's not all.

Climate change might make some of these hazards worse.

For this part of the story, we need to head out to the coast.

Remember, the Juan de Fuca plate is diving beneath the North American plate, pushing it up.

The rate of uplift hasn't quite kept up with sea level rise, but it certainly meant less of it so far.

But that won't last.

When the earthquake hits, the plates will shift and the land level will drop or subside by up to six feet.

- That is basically equivalent to a few centuries of climate driven sea level rise that can occur basically within minutes.

- Floodplains across the West would expand by up to 115 square miles.

Permanently putting more houses, businesses, and infrastructure in harm's way.

- We found that that expansion of the floodplain would basically double the flood exposure of people, structures and roads.

- But if the earthquake doesn't happen until 2100 sea levels will be higher, meaning subsidence would be happening on top of the already expanded floodplains.

- Then if a large earthquake occurs, the land drops down and you end up tripling the flood exposure.

- Okay, so this all feels really dire.

Should everyone living within a hundred miles of the Pacific Northwest coast just find somewhere else to live?

Well, we know there's nowhere that's safe from climate risk, and we also know that this is a problem we know how to solve.

There's a lot of work to be done to retrofit buildings, bridges, and critical infrastructure, but it can be done.

- We know that with modern construction of fuel tanks that are built to the appropriate codes, they can be built and designed to resist that magnitude of shaking.

- And beyond retrofits.

There's a lot that in individuals can do to prepare.

And it's not what you might think.

We made a whole episode about what to put in your go bag.

But being prepared isn't just about supplies.

- After any kind of disaster there's a lot of prosocial behavior.

People really come together.

- Emergency response expert Alice Busch says the single most important thing you can do.

Get to know your neighbors.

- You will know a little bit more about what maybe they're gonna need from you, and maybe they're gonna know a little bit more about what you're gonna need from them.

Whether that's medical provision or the fact that they are a ham radio enthusiast, or maybe they're a nurse.

Those skill sets people give freely in the immediate aftermath of a disaster.

- Make sure to know the risk that your home, school, or workplace faces.

Make a plan with your family and friends for what to do in different scenarios and talk to your neighbors both at home and at work.