Short Wave - Discovering 'Stormquakes'

Episode Date: February 5, 2020

Seismologist Wenyuan Fan explains the accidental discovery — buried deep in seismic and meteorological data — that certain storms over ocean water can cause measurable seismic activity, or 'stormquakes.' He says this phenomenon could help scientists better understand the earth below the sea.The original paper Wenyuan co-authored on stormquakes is here. Follow host Maddie Sofia on Twitter @maddie_sofia. Email the show at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. If you were in Seattle, Calgary, or Juno, you might have felt it. October 28, 2012, a 7.8 magnitude earthquake struck off the coast of Canada, near the archipelago of Haida Guay. Earthquakes aren't unusual in that area because there's a big fault line nearby. But it turned out, buried in the data associated with this earthquake, was something unusual. We were not particularly looking for something, but we were trying to look for earthquake evolution processes. When you and Fan is a professor at Florida State University. I am a seismologist, or you can say a geophysicist in a more general term.

And so a couple years back, when he was looking at the data from the 2012 earthquake off the coast of Canada, he noticed that before that big earthquake struck, there were records of what looked like. smaller earthquakes nearby. Just migrating from north to south. And by noticing that, I thought I found a precursor to the earthquake, and that was quite exciting to me. And that would have been pretty cool on its own, a previously unknown precursor to a big 7.8 earthquake.

But just to make sure it was a real thing, when you looked at some data from two years before and the year after. So not only 2012, but 2010, 2013. And what we started to find is that such activities would happen every year. Huh. But only happen during winter times. So those smaller earthquakes in the ocean weren't a precursor to the big earthquake after all. Because they happened before it and after it too.

Now, you don't have to be a seismologist to know that earthquakes don't exactly know when it's wintertime. That's right. That's right. Right. Yeah, earthquakes aren't seasonal, right. they kind of just happen when they happen. But the weather is seasonal. Sure is.

So that was a eureka moment saying, well, the seasonality of this seismic activity obviously is quite important. What Wenouin and some of his colleagues would later confirm is that storms out in the ocean were causing what they say is a seismic phenomenon that they never knew about before. Instead of finding earthquakes, we found some. Stormquakes. Storm quakes.

This episode, how they happen, and what they could teach us. I'm Maddie Safaya, and this is Shortwave, the Daily Science Podcast from NPR. So, stormquakes. We're not talking huge quakes. We're talking small quakes beneath the ocean floor, maybe 3.5 or so in magnitude. Not something you're necessarily going to feel from land, but definitely a new phenomenon to scientists. And to get why they're important, let's go back. when Wenewan fan first stumbled across them in the Pacific Northwest.

He and his fellow researchers had records of storms, synced up with records of seismic activity beneath the ocean floor. So maybe by now you're thinking what Wenuan was thinking. I do have to say, waves. The name of the show is quite compatible with the study. That's so true. As Wenuin and his colleagues outlined in their paper in the journal Geophysical Research letters, stormquakes all come down to waves. Because when you have large storms, it will couple with the ocean and make high waves.

Gotcha. And by doing the cross-examination of the ocean waves and the seismicity, we start to see a clear correlation between the occurrence of stormquakes and also the high wave conditions. Gotcha. And what was your reaction when you first kind of realized that correlation? Had anybody hypothesized about that possibility before? I was quite confused, to be honest. That's the beginning of science, you know what I mean? That is correct.

So one reason that this was a confusing result is that, like we said, seismic activity is not unusual in the part of the Pacific Northwest that Wenuin was looking at. There was a chance the data could kind of be contaminated by other seismic activity in the region. But it turned out... Storm days correlating with stormquakes. It's also observed offshore New England. For example, near Cape Cod, where I did my postdoc. So in that region, there are no faults.

We don't really have earthquakes there. Right. Okay. And during storm days, we see such activities during calm days, we do not. But the closer he looked, when you ensaw that a stormy day doesn't always equal a quakey day, even if the storm happens to be a powerful hurricane. For example, Hurricane Sandy off the coast of New Jersey, 2012, no stormquakes. Hurricane Bill, in 2009, also a northeast coast storm, generated hundreds of stormquakes. The difference, Wen says, is that you need a special combination of strong ocean waves,

interacting with the right type of topography on the seafloor. And one thing particularly important that is required to excite stormquakes is a sea floor topography feature called Ocean Banks. Okay. So an ocean bank is like a hill on land. And when such seafloor topography feature is present near the continental shelf, the interaction between the ocean waves and the sea floor topography would produce a storm quick. Gotcha.

So like, okay, this might be hard. But so I'm underwater. So I'm underwater. Yes. I'm looking at like this ocean bank is the idea that the storm kind of like pushes the water into that bank and the way that the water interacts with that seafloor pushes and creates. Help me out when you want. Right. No, you're almost there.

So what really happened is actually an interesting unknown process. But our current understanding of the process is when storms are approaching the coastlines, it starts to drag the ocean surface. That's why we have high waves. When these high waves propagate towards the coastline, it starts to create a new type of ocean waves, which is called infrared waves. This kind of infrared waves would have much longer wavelengths.

Gotcha. And because of that, it can touch the seafloor. Oh. Once it's able to touch the seafloor, that's the initiation of interaction between these ocean waves and the seafloor topography. So, okay, all right, all right, I'm going to try it. So, you know, like a hurricane moves through,

and as it moves across the water, it drags the water on the surface creating a wave. And those waves are big enough or powerful enough that when they crash back down, they can actually interact with the seafloor, and that is what, you know, like initiates a stormquake. Yes. Hey!

Not bad. I'm getting it. Very good. I'm getting it. Very good. As you can hear, y'all, physics, not my strong suit. So, you know, in the physics world, everything is a wave, right? So the seafloor topography, if you think about that, it is also a type of wave. It's just this wave doesn't move. It has the shape of up and down, but it is a frozen wave. You're blowing my mind right now. Think about that. It makes sense, right?

So it has up and downs, it has the shape of a wave, it just does not move back and forth. But the ocean waves can move around. And because of that, the interaction between the sea floor topography and the ocean wave is almost inevitable. In the datasets that Wen sampled, they found over 14,000 stormquakes off both U.S. coasts over roughly a nine-year period beginning in 2006. That's more than 1,000 each year. year, which raises the question. Shouldn't somebody have noticed this before? You know what? We asked the same question as well. We can't be the first. The answer has something to do with how seismic data is gathered, via thousands of seismic

sensors all over the world that are constantly recording huge amounts of data. In reality, only about 5% of those records are about earthquakes, and the remaining ones are recording everything around us, a car driving by the ocean, and someone doing a dance lesson. So without knowing where to look for or what to look for, it is actually kind of hard to harness the power of those seismic data to extract useful information. Gotcha. So it is only because we designed a new method that deals with continuous data to process them in large scales. That is how eventually led us to.

the finding of stormquakes. I see. So it's almost like there was too much data out there to be able to find a pattern like this without, you know, some like big computational abilities. Yes. Although to a seismologists, there is never such a thing of too much data. You know what? I get it. I get it. When Nguyen and his colleagues still have a lot of questions about stormquakes. Like how exactly the water interacts with the seafloor to produce them. But simply knowing that stormquakes exist could provide an entirely new source of information about the earth below the sea floor.

Traditionally, when we image the earth structures, we need a signal that is clean, that is simple, and that is recognizable, right? So the stormquakes are like flashlights traveling through the earth and get to be picked up by seismometers. And now by using these stormquakes like lights. illuminating the subsurface, we will be able to know a little bit more about the subsurface structure and potentially the long-term tectonics. So using information that we can get from stormquakes that will help us kind of understand what the earth looks like even below the ocean floor? Yes.

Awesome. That's cool. I like that. Shining in a little light all the way down to that crust. What are you doing down there? What do you look like? Yes. You talk to the earth like that all the time when you are? Yes. Okay, because I think if you haven't, you should start trying it, you know. That's right, that's right. Hopefully it will give me some answers.

When you win fan at Florida State University, we've got a link to his paper on stormquakes in the episode notes. This episode was produced by Brent Bachman, fact-checked by Emily Vaughn, and edited by Viet Le, who is celebrating a birthday today. Happy birthday, Viatt. We are so glad you were born. I'm Maddie Safia, and we're back with

More shortwave from NPR tomorrow.