Emily Kwong (2:22)

We don't know when.

Hannah Chin (2:23)

We can't predict it at all. One scientist I talked to, his name is Chris Goldfinger, and he's a marine geologist and paleoseismologist at Oregon State University. He said they don't even use that word.

Chris Goldfinger (2:34)

Prediction is sort of in the science world as we call it, the P word. We just don't really even speak about it because nobody can do it.

Emily Kwong (2:42)

The P word. We don't do that in earthquake science.

Hannah Chin (2:45)

And listening to this, Emily. I was like, why is that right? Why do we know so many concrete details about certain parts of this looming disaster and then zero details about this other seemingly really crucial part of when is it gonna happen?

Emily Kwong (3:00)

Today on the show, the earthquake prediction problem, what we know and what we don't about quakes like the big one and how the science is shifting under researchers feet. You're listening to Shortwave, the science podcast from NPR Foreign.

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Emily Kwong (4:24)

Okay. Hand. Today we are talking about earthquakes and the difficulty of predicting them, which is kind of scary when it comes to the magnitude 8, the magnitude 9 ones, the big ones. But how do you know a big one is coming for the Pacific Northwest?

Hannah Chin (4:37)

That's a great question. So first, there's geologic clues of past earthquakes in the landscape. There's what we call ghost forests, these thousand year old trees on the Oregon and Washington coast that seem to have been submerged in seawater really quickly. And then in other places, you can find sand deposits in the soil that must have come from big earthquakes. And second, there's also more specific records that we have, human records from somewhere clear across the other side of the world, Japan.

Emily Kwong (5:03)

Oh, that makes sense because Japan is extremely earthquake prone. It sits at like the confluence of multiple tectonic plates.

Hannah Chin (5:09)

Yeah, exactly. So when a big earthquake hits there, it's often followed by a tsunami wave. It goes like earthquake, tsunami, earthquake, tsunami. But in the year 1700 on January 26, Japanese scholars have all of these records of what they called the quote unquote orphan tsunami. Orphan because they didn't know where it came from. It just didn't seem to have a parent earthquake preceding it.

Chris Goldfinger (5:33)

And this tsunami Arrived out of nowhere with no earthquake to go with it, no warning. It killed a few people, destroyed some boats and destroyed bales of rice in warehouses. And they had written records of this.

Hannah Chin (5:45)

So this is Chris again, the seismologist. He says the Japanese records were really accurate down to the height of the flooding and the amount of the destruction. And using these records, it was possible for scientists to do some detective work and figure out where that big wave came from.

Chris Goldfinger (6:00)

And so Kenji Sataki, a Japanese colleague, modeled the tsunami. You know, where did it come from? Did it come from Alaska or Kamchatka or Chile or wherever? And the only place that matched was.

Hannah Chin (6:12)

Cascadia, which, Emily, again, is that fault line right off the Portland coast. So that research is how we know that the last great earthquake in the Pacific Northwest was January 26th, the year 1700, about 9pm that is so precise.

Emily Kwong (6:27)

It's incredible actually that they were able to track the last, you know, big one in the region to that moment in time, 325 years ago.

Hannah Chin (6:35)

No, it's really cool. And scientists have done more modeling. They've researched earthquakes in the area further and further back. They've talked to indigenous people who have told stories about these quakes for generations. And they've realized that Cascadia has these really big earthquakes, usually magnitude nines every 500 years on average.

Emily Kwong (6:52)

Oh, then we're fine. Right. Because if the last big one was in 1700, that's way less than 500 years ago. So it's fine. Right.

Hannah Chin (7:00)

So this is what I thought too, but Diego told me it's not that simple.

Diego Melgar (7:04)

Earthquakes can cluster in time, so it can be that every now and then the Earth earthquakes happen in quick succession. So we could have a few magnitude nines, only 250 years apart, then maybe a thousand year period of calm, then a quick succession of other big earthquakes. So Even though it's 500 years on average, it is not the case that they happen. 500 years, nothing earthquake. 500 years, nothing earthquake. That's not how Earth works. I wish it were.

Emily Kwong (7:35)

These tectonic plates are like, we don't follow rules, we don't observe patterns.

Hannah Chin (7:39)

Yeah. So we could be due for a major earthquake or we could be fine for the next 500 plus years.

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Either or.

Emily Kwong (7:46)

Okay.

Hannah Chin (7:48)

Our other seismologist, Chris, he compared it to figuring out when your Thanksgiving turkey is ready. If all you did was stick it in the oven and walk away.

Chris Goldfinger (7:56)

Somebody says, is it almost done? Well, I don't know. When did you turn it on? I don't Remember? And you see the oven sitting there at 350 and you go, well, how long has it been gone at 350? I have no idea. And you don't have a turkey thermometer either. So you have no way of measuring when the cycle started or how far into it you are or how cooked it is.

Emily Kwong (8:15)

That sounds like how I cook. Point is, earthquakes are like chaotic turkeys.

Hannah Chin (8:22)

Right. And just to complicate this a little further, Emily, because I know that's what you're dying to hear, we don't even know for sure that this will be a magnitude 9 earthquake. It could be a little bit smaller, catastrophic, but not quite that big. Okay, but here's what we do know.

Diego Melgar (8:35)

We have really good idea of what the tsunamis are going to look like and what the shaking is going to look like. And that's actionable information that we put to use.

Emily Kwong (8:43)

That's important because since earthquakes can cause tsunamis, knowing what different size earthquakes will do to the land, to the water, is really important for human health and safety.

Hannah Chin (8:55)

Yeah. And so that's the second part of this story. There's all of these things about earthquakes that science can and does predict, like what could happen when the big one hits.

Emily Kwong (9:04)

How do scientists figure that out? Just knowing, like, if it's a X magnitude earthquake, it will do this.

Hannah Chin (9:10)

They look for clues from the past and they can find those in places like estuaries and tidal marshes.

Tina Dura (9:15)

So when we have a big Cascadia earthquake, tsunami washes in sand and deposits it on these marshes. And that sand is then preserved in the stratigraphic record, so in the coastal sediments over time.

Hannah Chin (9:29)

So this is coastal geologist and paleoseismologist Tina Dura. She works in the geosciences department at Virginia Tech.

Tina Dura (9:35)

We actually go out there with a tube and push it down into the ground. And, you know, the oldest earthquakes are at the bottom of the record. And as you go up towards the surface in the sediments, you see the younger earthquakes. And in some of these marshes, we have up to a 7,000 year record of past earthquakes.

Hannah Chin (9:54)

Tina showed me a picture of one of these sediment core samples. It kind of looks like a layer cake. You can see the marsh dirt and then the tidal dirt on top of it, and then the tsunami dirt. And then it goes all over again.

Emily Kwong (10:03)

It's like reading tree rings. It tells the story of the geology. What does looking at a record like that tell her?

Hannah Chin (10:10)

She told me that between earthquakes, basically, when there's pressure building up on these tectonic plates, it causes the land to rise. Which, for what it's worth, is part of the reason that climate driven sea level rise hasn't really affected the coastlines of the Pacific Northwest the way it has, say, the Gulf of Mexico, et cetera, because the land is rising along with the ocean. It's rising at about 1 millimeter a year.

Diego Melgar (10:34)

Whoa.

Tina Dura (10:34)

But of course, the next earthquake is going to reverse that. And this land level change, where it goes down is going to happen over minutes, and it's going to cause a sudden sea level rise of up to 2 meters.

Hannah Chin (10:47)

Combined with the already existing tsunami waves that were predicted to have, you'd get flooding, a lot of flooding, mostly in low lying areas along the coast. The places that are flat and easy to build on, where there are already airports and fire stations and wastewater treatment plants. And unlike tsunamis, where the flooding comes in and then goes away. Tina said the combination of the land drop and the waves is going to mean a much more permanent change to the landscape.

Emily Kwong (11:14)

So whole areas might stay flooded.

Hannah Chin (11:17)

Yeah.

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Wow.

Hannah Chin (11:18)

And the other thing that's important to know, Emily, is that this might not just affect the upper half of the West coast, it could also trigger another earthquake further south, the California big one. So just south of the Cascadia fault is this other tectonic plate boundary called San Andreas fault, and that one's responsible for a lot of earthquakes in California. Remember Chris Goldfinger? He's the paleoseismologist we heard from earlier.

Emily Kwong (11:43)

Yeah, the one with the incredible Turkey metaphor.

Hannah Chin (11:46)

Absolutely. So in 1999, through a clerical error, he and his research team ended up sailing too far south and taking a sample of the San Andreas fault. And as they were comparing these samples, one from the Cascadia fault and one from the San Andreas fault, they realized that all the events that these cores recorded were happening super close together, just time wise, which is super weird. Right. So they took way more samples, they got way more data, and they realized that the Cascadia and the San Andreas were what geologists call seismically linked. They have the potential to trigger earthquakes in one another.

Emily Kwong (12:21)

That sounds like a big bad set of dominoes, just like tipping down the West Coast. Okay, so more flooding, more landscape change, bonus earthquakes. Is there anything else we should know about the big one? Like is it just gonna be, or are we just powerless in the face of it?

Hannah Chin (12:37)

We are not. There's good news because in the past few decades, scientists have developed the technology to create an earthquake early warning system.

Diego Melgar (12:46)

The idea is quite simple. We need seismometers, sensors that feel the first teeny Tiny vibrations.

Hannah Chin (12:53)

Diego told me we have thousands of these little sensors located all throughout Washington and Oregon and California. And they're all just listening to the Earth, waiting to hear these tiny, tiny vibrations.

Diego Melgar (13:05)

And using decades of research and models, we know that if the teeny, tiny vibrations look a certain way, then these teeny, tiny vibrations are not from a 5, they're not from a magnitude 6, they're probably from magnitude 8 or from a magnitude 9. And after a few of these seismic stations detect these teeny tiny vibrations, then all the logic algorithms and technology kicks in and the alert goes off by cell phones, by emergency sirens and so on. And it says, you know, earthquake drop, cover and hold on.

Hannah Chin (13:36)

This entire early warning system can be activated in 15 to 20 seconds, totally automated, without any human action.

Emily Kwong (13:43)

That's astonishing. I mean, 15, 20 seconds doesn't sound like a lot of time, but just even a little bit of advanced warning could be the difference between life and death, you know?

Hannah Chin (13:50)

Yeah, exactly. And all the scientists that I talked to, they told me it's really good to know everything we can about how this big earthquake will play out, even if we don't know exactly when it'll play out.

Diego Melgar (14:02)

This is the point in the conversation at which I tell people, knowledge is power, and I'd rather know that these are the challenges we're facing, that the tsunami is probably going to be this size, that the shaking is probably going to be this intense. Because armed with that knowledge, I can develop goals and objectives.

Hannah Chin (14:18)

And Diego says that's the next step. Right. If you're in the Pacific Northwest and especially if you're in a coastal town, make sure you have those goals and objectives. Make sure you have a flooding plan. Ask your neighbors if they have one, because when this happens, it's likely that medical experts won't be able to reach everyone. So we're going to need to rely on other people in our communities. Find out whether your state agencies and local emergency managers have an earthquake plan or write a letter to your legislators and ask them to push for earthquake proof buildings and evacuation centers. Yeah, it's going to take time, but Diego told me we're making progress. We have everything that we need to prepare.

Emily Kwong (14:56)

Hannah Chin, you have repped your region well to get ready for this. Thank you for bringing this to all of us.

Hannah Chin (15:03)

Thank you so much for having me.

Emily Kwong (15:06)

Troyvers, if you have a question about your local environment, open up your phone and record us a little voice memo about it. You know your feelings, your thoughts, your observations, and then email that voice memo to shortwavepr.org we will listen and may even build an episode around your question.

Hannah Chin (15:21)

Also, if you want to learn more about earthquake science and seismometers, you should check out another episode we did a while ago. We'll link to it in the show.

Emily Kwong (15:28)

Notes this episode was produced by Hannah and Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez. Tyler Jones checked the facts and Kwesi Lee was the audio engineer.

Hannah Chin (15:37)

Beth Donovan is our vice president of podcasting. And special thanks to Paul Lundgren and Suzanne Carbot, whose research and expertise helped inform this episode.

Emily Kwong (15:45)

I'm Emily Kwong.

Hannah Chin (15:46)

And I'm Hannah Shin.

Emily Kwong (15:48)

Come back for more shortwave from npr. See you later.

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