S1 E9: The Big One with Harold Tobin and Audrey Dunham

Earthquakes can strike at any moment. On the final Season 1 episode of FieldSound, UW seismologists Harold Tobin and Audrey Dunham discuss the impending threat of “The Big One” - a large-scale earthquake that will strike along the Cascadia Subduction Zone. Tobin and Dunham also share recent advances in earthquake and tsunami preparedness for communities inland and along the coast in the Pacific Northwest.

Harold Tobin is a professor in the UW Department of Earth and Space Sciences and holds the Paros Endowed Chair in Seismology and Geohazards. He is also the Director of the Pacific Northwest Seismic Network, and the designated Washington State Seismologist, studying tectonic plate boundaries, how faults work, and the conditions that lead to earthquakes.

Audrey Dunham is a UW Department of Earth and Space Sciences Postdoctoral Scholar working with the Cascadia Coastlines and Peoples Hazards Research Hub (CoPes Hub) focused on ground motion simulations of potential Cascadia Subduction Zone earthquakes and quantifying hazards for coastal communities in the Pacific Northwest.

The Pacific Northwest Seismic Network is supported by the Friends of Earthquakes fund.

https://environment.uw.edu/podcast

Transcript

00;00;00;04 - 00;00;15;05
Audrey Dunham
We don't know what the earthquake will look like, but the best thing we can do is test a bunch of different scenarios, kind of getting getting at, like I said, those ranges of ground shaking that we might feel so that communities are more prepared for that.

00;00;15;08 - 00;00;17;10
Audrey Dunham


00;00;17;12 - 00;00;25;04
Sarah Smith
The from the University of Washington College of the Environment. This is field sound.

00;00;25;07 - 00;00;37;25
Sarah Smith


00;00;37;28 - 00;00;58;26
Sarah Smith
If you're from the Pacific Northwest, you likely know about the threat of the big one, a massive earthquake that's likely to cause catastrophic destruction. And we wouldn't know exactly when that would happen, just that it could happen at any moment and that we should be prepared.

00;00;58;28 - 00;01;14;00
Sarah Smith
But how exactly do you prepare for an earthquake and what exactly is an earthquake? Where do they come from and what will it be like?

00;01;14;02 - 00;01;32;07
Harold Tobin
The source where it's coming from is actually a slip on a fault. So a fault is just a kind of a break in the crust of the earth, a place where there's to, you know, absolutely gargantuan scale bodies of the Earth's crust rock that are pressed up against each other. And the plates are trying to move.

00;01;32;10 - 00;01;56;05
Sarah Smith
Harold Tobin is a UW professor in the Department of Earth and Space Sciences. His research involves the study of tectonic plate boundaries with a focus on how faults work and the conditions inside them that lead to earthquakes. He's especially interested in subduction zones where the planet's largest earthquakes and tsunamis take place. Tobin is the designated Washington State seismologist.

00;01;56;07 - 00;02;34;18
Harold Tobin
And I'm also the director of something called the Pacific Northwest Seismic Network, which is the research center that basically runs all the seismometers we have in Washington and Oregon. So if you hear about an earthquake happened and you know the magnitude and when and where that does, but these these massive scale plates, the Pacific Ocean floor, which is called the one to Fuca plate and then the North American plate, are sort of trying to to converge on each other and the plates are trying to move and they stick and they go at an incredibly slow rate on a human time scale like a few inches a year, but over hundreds of years that, you know,

00;02;34;18 - 00;02;54;22
Harold Tobin
that that builds up a strain just in the same way that if you pull the string back on a bow, you're bending the bow, right? And eventually the strain is so much that it's going to release and that plate slides over the other plate and that sliding stands out. All those waves and those ripples that that we feel as the earthquake.

00;02;54;24 - 00;03;01;08
Harold Tobin
So the larger the area over which that happens and the more it slips, the bigger the earthquake.

00;03;01;11 - 00;03;08;19
Sarah Smith
When we talk about earthquakes, we talk about magnitude or the size of the earthquake. How are earthquakes measured?

00;03;08;22 - 00;03;32;08
Harold Tobin
It's like everybody here is oh, it's a magnitude eight. It's a magnitude nine. It's magnitude 4.2, whatever. That's a scale of basically how how large the earthquake slip was and also how strong the the waves were that that came out from the earthquake. It's a scale that's logarithmic. So it's really important to recognize that they get so much bigger.

00;03;32;11 - 00;04;01;01
Harold Tobin
You know, a magnitude nine is the equivalent of 30 magnitude eights, and an eight is the equivalent of 37. So a nine is 900 times bigger than a magnitude seven. And you know, you can multiply it by 30 again, 18,000 times bigger than a magnitude six. So when we talk about earthquake of a three or four or five, those are big enough for people to feel, but they're really nothing remotely like what these very large earthquakes are like.

00;04;01;04 - 00;04;04;07
Sarah Smith
And what about intensity or how the earthquake is felt?

00;04;04;10 - 00;04;25;24
Harold Tobin
What you feel depends on how far away you are and the kind of ground you're standing on and whether you're in a tall building or a low building and all kinds of things like that. So we call that the earthquakes intensity. So the intensity varies with your location. You could feel a very strong intensity if you're close to the earthquake and nothing at all or a very low intensity far away.

00;04;25;26 - 00;04;43;08
Harold Tobin
The analogy I like is that the earthquake magnitude is like the wattage of the light bulb of a light bulb. So, you know, it just has a wattage. It's putting out a certain amount of light, how bright it is, where you are. That's the intensity of the light bulb. If you're far away, you barely see it. You barely see the light from it.

00;04;43;10 - 00;04;55;21
Harold Tobin
So that that's a distinction. So anyway, so we tend to talk about earthquakes in their magnitude because that that's a common thing for anyone who, you know, who is in the area that experiences that describes that earthquake.

00;04;55;24 - 00;05;22;29
Sarah Smith
Washington State is earthquake country. Growing up in this region, we practiced earthquake drills in school, drop, cover and hold. Yet there are many here in the northwest that have never experienced an earthquake. The last big earthquake in this area was in 2001, a 6.8 earthquake that caused destruction in the Puget Sound region and lasted nearly a minute. The big one will likely feel different.

00;05;23;01 - 00;05;41;09
Harold Tobin
In the northwest. You know, we have earthquakes from time to time. We tend to go a long time between earthquakes that people really feel here in our region, which creates some complacency. But really, you know, that doesn't mean they're not potentially going to come in the future. But we know they will. And that's that's a challenge. There's really more than one type of large earthquake that could happen.

00;05;41;09 - 00;06;11;05
Harold Tobin
But everybody talks about, you know, the potential for the big one. Right. And what we mean by that in the northwest is one of these offshore earthquakes, mostly offshore. That is where the two plates meet and one slides beneath the other. So-called subduction zone. Then in the Cascadia subduction zone. We know now through an incredible amount of sort of geological sleuthing and kind of inference, that place has the possibility of a magnitude nine scale earthquake.

00;06;11;08 - 00;06;33;20
Harold Tobin
And these are the largest earthquakes that the planet has. There have actually only been five magnitude nine since we started having seismometers well over a hundred years ago on the whole planet. So what is what does that mean? What is what is the big one? In our case, it's the potential for an earthquake where the actual fault lies at the coast or just offshore of Washington, Oregon, Vancouver Island, even northern California.

00;06;33;22 - 00;06;54;24
Harold Tobin
But that doesn't mean it's not going to shake us here inland in a place like the Puget Sound. Those earthquakes are so big that the shaking could be very strong and go on for not seconds, but several minutes long. The break of the fault happens so suddenly it spreads over the fault in a matter of seconds or less than a minute or so.

00;06;54;26 - 00;07;02;29
Harold Tobin
And so all we have is the ability to detect that earthquake as it's getting started, but not really to to show it in advance.

00;07;03;02 - 00;07;12;26
Audrey Dunham
There's a lot of unknowns in seismology. And I think the particular one that's been stumping seismologists since the field started is how we can predict earthquakes.

00;07;12;29 - 00;07;26;01
Sarah Smith
Audrey Dunham is a post-doctoral researcher at the University of Washington, focused on quantifying seismic hazards, using large scale ground motion simulations of potential Cascadia subduction Zone earthquakes.

00;07;26;03 - 00;08;07;10
Audrey Dunham
For my postdoc research, I'll be simulating the ground motion from different scenarios of large Cascadia subduction zone earthquakes. That's basically so that we can get a understanding of the kind of ranges of ground shaking that our population centers, our communities in the Pacific Northwest might feel from these earthquakes. So we don't know what the earthquake will look like, but the best kind of thing we can do is test a bunch of different scenarios, kind of getting getting at, like I said, those ranges of ground shaking that we might feel so that communities are more prepared.

00;08;07;12 - 00;08;14;24
Sarah Smith
What data do scientists use? What do these models consist of and what can they tell us? How do they work.

00;08;14;26 - 00;08;40;10
Audrey Dunham
For an earthquake are where the actual epicenter of the earthquake is located. How much slip or how much motion is along that fault and then how fast it's going. So we put all of those kind of things into our model. We also need to know about the Earth structure, which is basically how fast these waves are traveling through the rock where the earthquake is happening.

00;08;40;12 - 00;09;05;22
Audrey Dunham
And these are important because they either increase the ground shaking or decrease it in different ways. And we put these into a numerical model where we basically use supercomputers to calculate how those waves are traveling in 3-D. And then we pick at each location on the surface where we want that information. The output of our simulations or our models are actually seismic rams at the surface.

00;09;05;25 - 00;09;12;26
Sarah Smith
Researchers create models that essentially lay out potential scenarios of what a Cascadia earthquake might look like.

00;09;12;29 - 00;09;30;24
Audrey Dunham
And with that, we'll be doing a couple tsunami simulations. So we'll have these earthquake and we'll simulate the ground shaking that the the earth will feel will also simulate a tsunami that could happen from that to.

00;09;30;26 - 00;09;56;17
Harold Tobin
The coast of our state is likely to experience a tsunami of the scale of some of the biggest ones we've ever seen, like what happened in the Indian Ocean in 2004 or Japan in 2011, a little more than a decade ago. And so preparing for that is really important. Fortunately, we don't have really big cities on the outer Pacific coast, but we do have plenty of people who are living there or vacation there.

00;09;56;20 - 00;10;18;02
Harold Tobin
And the shaking, you know, is is potentially a hazard, but maybe even more of the hazard is just knowing that you have to get away from the potential tsunami inundation zone. If you feel strong shaking up the coast, you want to be secure during the earthquake, drop, cover and hold on. But as soon as the shaking is over, look at whether you need to to move to higher ground.

00;10;18;04 - 00;10;25;04
Harold Tobin
It's really important that people know that. So that like happened in Japan, you know, most people can actually escape and save their lives.

00;10;25;07 - 00;10;48;22
Audrey Dunham
I think there's been some really important progress on the coast recently, including the building of vertical evacuation structures. Some communities are in locations where it's just not feasible by foot to get to higher ground out of a region of a tsunami. So they build these structures that are high enough to get people into safety without actually having to run to higher ground so they can just walk up these structures and kind of stand.

00;10;48;27 - 00;10;54;25
Audrey Dunham
They really improve the hazard models in their regions because they build this vertical evacuation structure.

00;10;55;02 - 00;11;13;04
Sarah Smith
Adria is also applying her expertise as postdoctoral researcher with the Cascadia Copes Hub. Her work with large scale simulations can help improve our understanding of geologic hazards for coastal communities and positively impact earthquake and tsunami preparedness measures for communities on the coast.

00;11;13;06 - 00;11;42;27
Audrey Dunham
The Copes hub or the Cascadia Coastlines and People's Hazards Hub. It's a group of researchers that have a main goal of increasing resilience of coastal communities to things like natural hazards as well as climate change. Copa, I think, will really help to work with people who are already kind of doing these things. And I'm on the team that focuses on the geologic hazards, but there's also teams looking at how this impacts the communities and how we can increase.

00;11;42;27 - 00;11;51;00
Audrey Dunham
There their resilience using kind of our our new models that will be producing.

00;11;51;03 - 00;12;17;22
Sarah Smith
The recent tragic earthquakes impacting Turkey and Syria serve as an example of how unpredictable and devastating earthquakes can be. And also why it's important to prepare. Earthquake experts like Carole Tobin and Audrey Dunham offer a few words of advice to remind us that when we prepare, we improve our chances to mitigate loss, and we're more likely to make it through a big earthquake just fine.

00;12;17;25 - 00;12;43;12
Harold Tobin
Most people come through fine from even bigger earthquakes, and that will be true here as well. Most people don't realize that that normal wood frame houses like single family sized houses, one or two or three storey buildings are pretty safe buildings to be in for the most part in earthquakes. They're not likely to collapse in these these events, except the ones that are shaking the absolute hardest, and that's a small percentage of the total.

00;12;43;15 - 00;13;09;24
Harold Tobin
The Japan tsunami is another example where it was a terrible disaster. 19,000 people lost their lives in that tsunami, but something like 350,000 were are known to have been in the tsunami sort of fatal zone at the time of the earthquake. So between the earthquake and when the tsunami washed ashore, almost 95% of the people you've got out of that zone and were safe.

00;13;09;26 - 00;13;23;09
Harold Tobin
And it's terrible that people lost their lives. And of course, we need to do better. But again, it's just a reminder that that these disasters are not so all encompassing, that we should just throw up our hands and not prepare.

00;13;23;11 - 00;13;43;01
Sarah Smith
In an earthquake. Every second counts. And preparedness is key. Shakealert is another tool that can potentially protect lives from the destruction of earthquakes by notifying people just seconds after an earthquake begins. Via mobile apps, emergency alerts on cell phones and public address systems in buildings.

00;13;43;04 - 00;14;03;27
Harold Tobin
In the past five, seven years or so, we've really built up and actually doubled our capacity in the region because of this new earthquake early warning program, which is a way to, you know, detect earthquakes as they begin and give people sort of ten, 20, 30 seconds or more of warning before the shaking actually starts. It's a whole new game.

00;14;04;03 - 00;14;26;18
Harold Tobin
If you feel shaking or if you get one of these shakealert messages that comes in on your phone, then, you know, move away from anything that looks like an object that could really topple on you, but drop cover and hold on and get under the table. Get under something sturdy because most injuries actually come not from the building collapsing, but from objects falling, you know, within within a room or a space like that.

00;14;26;20 - 00;14;47;23
Harold Tobin
And then secondly, you know, know how to be prepared for the disruption and the aftermath. So have your your your go bag that has some some food and flashlight and, you know, know your communications system, maybe have a family plan to to to know, you know, where you'll meet up if the cell phones aren't working in your different places after the event.

00;14;47;25 - 00;15;06;19
Harold Tobin
Something like that is worth worth at least talking about once a year. Just being aware of you can go for all kinds of information on what should be in your so called two weeks ready bag or you know sort go kit. The Washington State emergency Management Department, Washington AMD has a great website and they have all kinds of information on earthquake preparedness.

00;15;06;19 - 00;15;25;26
Harold Tobin
They're a great place to go. There are also links at our Web site, which is PNAS and Pacific Northwest Seismic Network, dot org, PNAS and dot org, which we have all kinds of earthquake information there and a map of what's happening right now or in the last week or two weeks in our in our region.

00;15;25;28 - 00;15;27;15
Sarah Smith
All right. So be prepared.

00;15;27;20 - 00;15;32;02
Harold Tobin
Absolutely. Prepare not despair. That's my motto on earthquakes. That's a good one.

00;15;32;05 - 00;15;33;23
Sarah Smith
And it rhymes.

00;15;33;26 - 00;15;39;17
Harold Tobin
Exactly with the It's.

00;15;39;19 - 00;16;03;21
Sarah Smith
A thank you to our guests, Harold Tobin and Audrey Dunham. To learn more about Harold and Audrey's work, Pinson in the Cascadia Copes hub, visit our Web site at Environment UW Talk Radio or click the links in this episode Description for all of us at Field Sound. Thanks for listening.