The Science Behind Devastating Earthquakes

17:30 minutes

Map of Marrakesh, Morocco - 2017
Credit: Shutterstock

On September 8, 2023 at 11:11 PM local time, a 6.8 magnitude earthquake struck Morocco’s High Atlas mountains. So far, more than 2,500 people died and thousands more were injured or lost. 

Other natural disasters usually give off warning signs; we can predict when a volcano will explode, ring the alarms when a tsunami starts to build, or evacuate before a hurricane makes landfall, but we still can’t detect earthquakes before they strike. And victims are left to face “the particular trauma that comes from watching the world around you crumble in an instant,” writes science journalist Robin George Andrews for The Atlantic.

Ira talks with Andrews about the specifics of this earthquake, where the science stands with earthquake detection, and the particular kind of trauma that comes from watching the world crumble.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Last week, a 6.8 magnitude earthquake struck Morocco’s High Atlas mountains. In this devastating disaster, thousands of people were killed. Thousands more were injured or are still missing.

What’s especially horrifying about earthquakes is there’s no way to know when they’ll strike. Scientists have been trying for years to look for signs before a strike, but nothing dependable yet. So what is the science behind the earthquake in Morocco? And are we any closer to predicting earthquakes? And if not, how do we prepare ourselves?

My next guest has been reporting on this earthquake. Dr. Robin George Andrews, volcanologist and science journalist based in the UK. Robin, thanks for joining us.

ROBIN GEORGE ANDREWS: Hey, thanks for having me.

IRA FLATOW: All right, can you walk us through earthquakes 101– what are they, how do they happen, what’s going on in this one?

ROBIN GEORGE ANDREWS: Yeah, so earthquakes, they’re like the ambushes of the natural world. Normally, when something is happening in nature, you at least get some sense that it’s on its way, or there’s some precursory signal. Earthquakes, they kind of just happen.

And an earthquake can happen anywhere where you have a fault line. And a fault line is basically just a sort of rupture in Earth’s crust, sometimes a bit deeper. And faults move side to side or up and down, or a combination of both, or apart sometimes.

And in any of these scenarios, if that fault moves quite suddenly, you can get quite a powerful earthquake because earthquakes happen all the time. An earthquake is just when the ground is shaking. But a powerful earthquake, the things that we are concerned about, are when a fault jolts forwards, up, down, sideways, in one way or the other. And depending on the size of this jolt and the energy released, you can get either an earthquake that just rattles things on a shelf, or you can destroy a city.

IRA FLATOW: You know, I have been following earthquake news for quite some time. And I don’t recall ever hearing of another big earthquake like this in Morocco.

ROBIN GEORGE ANDREWS: Yeah, so Morocco is a seismically active part of the world. It’s just a little different from the ones we normally think of. California’s a great example. California is pretty much smack bang on a major tectonic boundary. And as a result, there’s quite a lot of movement. You get quite a lot of earthquakes. There’s the potential for quite big earthquakes.

So Morocco sits on the African, or as some people call it, the Nubian Plate. And just above it, Europe sits on the Eurasian Plate. They move quite slowly relative to each other. So when you get a slow-moving fault, you can get earthquakes. But you don’t get large earthquakes because you’re not really building up stress. Nothing is moving quickly, then getting caught, and then jolting forwards.

So large earthquakes have happened. In 1960, for example, there was the Agadir earthquake. It killed about 12,000 people. So earthquakes aren’t uncommon, but large earthquakes are relatively rare in Morocco.

IRA FLATOW: Yeah, so how did this one happen in particular? You described a lot of different things that could go on. What specifically happened on the earth beneath our feet in this one?

ROBIN GEORGE ANDREWS: So yeah, this one was really tricky to– earthquake scientists to work out. They’re still trying to pin it down. I mean, one of the major surprises is the location of the earthquake.

So the seismic hazard was thought to be highest in the north of the country, near the coastline, because that’s near the tectonic plate boundary. That’s where you’d expect most of the pressure to be building up and then released. This actually happened in sort of central-ish part of the country. It’s kind of an odd shape.

The other thing is, the fault networks around these mountain, the High Atlas mountains, are not as well known as others. Some are really old. Some date back to Pangaea, the supercontinent that was around at the time of the dinosaurs, hundreds of millions of years old. Some of these faults were suspected to not have moved for eons, maybe before humans even evolved kind of level. And it’s really hard to tell if a fault has moved that far back in the past, the [? evidences ?] [? we ?] [? have. ?]

So in this case, what looks like happened was a very, very sleepy fault, one that most people didn’t have their eye on, thought was inactive, seems to be the one that kind of jolted forwards. And it just happened to jolt forward in an incredibly potent way. And it generated a lot of shaking, so much so that people felt it in Lisbon.

IRA FLATOW: Yeah. And how deep inside the Earth does this earthquake originate?

ROBIN GEORGE ANDREWS: So this one was incredibly shallow. So sometimes, earthquakes can happen, like, hundreds of kilometers deep. They’re kind of rare in terms of the ones that affect humans, but they can. But this one, I think it was 26 kilometers. So really, just a few miles beneath the surface, in a way.

And generally, when you get a shallow earthquake, more of that energy gets transferred to the surface. Like, the motions underground are coupled with the surface a lot more rigidly, often. So the shaking was a lot more intense because of the shallowness of the earthquake. So that was unfortunate.

IRA FLATOW: How do you know how deep an earthquake is? How does science estimate that?

ROBIN GEORGE ANDREWS: So we live in kind of a wondrous age, where a lot of science seems kind of magic, even to me, who’s trained in this sort of stuff. Seismology is a relatively young science. And it essentially is listening for– it’s picking up on the vibrations that are unleashed by earthquakes. And they come in different flavors.

And scientists 100 years ago were barely beginning to understand how to use these seismic waves to see into the Earth, to some degree. But in that time, scientists have managed to use seismometers all over the world, in the area. You know, they’ve used the motion of the ground with satellites in space. They can listen to this kind of symphony of seismic music that’s coming from the Earth, and match it up with ground movement they see at the surface. And they can use that to very accurately pinpoint not only how deep the earthquake was, but actually the specific fault that slipped kind of thing.

So it’s all in retrospect. It’s all after it happens, which is kind of part of the problem. But the fact that it can be done with this precision does give you some optimism for where the field will go in the future.

IRA FLATOW: There’s a huge difference in this case about how Marrakesh fared versus the villages in the High Atlas mountains faring, right?

ROBIN GEORGE ANDREWS: Yeah. Something that the seismologists often tell me is, like, earthquakes don’t kill people, buildings kill people. And that’s broadly true, really. I mean, the fact that we live in certain areas that have seismic hazards is the thing that makes the hazard. And a lot of deaths are down to bad building kind of construction.

Like, if you live in an area that has a seismic hazard, ideally, there should be funding to make your buildings resist the earthquake. Now, no building can resist any earthquake. But Japan’s a great example. I’ve been in Tokyo when there have been some fairly modest magnitude earthquakes.

And a lot of the skyscrapers there actually sway and wobble a bit. And it’s because they’re swaying with the motion of the ground, which stops them snapping and breaking, whereas in Marrakesh, some of the newer buildings kind of resisted the quake a bit more. It helped that the epicenter was also a bit far away.

But parts of the old town have no structures designed to resist earthquakes. So that suffered a lot more damage. And in the High Atlas mountains, like, whole villages have been razed to the ground. I’ve enjoyed visiting Morocco. And I’ve been to these mountains.

And the villages there, it’s, like, mudbrick construction, unreinforced masonry. Not only are they in valleys, but they’re also on the slopes of these mountains. And it’s just it’s exactly the kind of structure that unfortunately, stands no chance. You can drop to the floor, duck and cover all you like. But when your entire building is basically becoming a fluid, there’s nothing you can do, really.

So it’s unsurprising that that’s where most of the damage was. It didn’t help that the epicenter of the earthquake was basically in that area. But it doesn’t make it any less tragic. Entire villages have been obliterated. It’s quite unfathomable, really.

IRA FLATOW: In a story in The Atlantic, you wrote that earthquakes carry their own trauma. What do you mean by that?

ROBIN GEORGE ANDREWS: Yeah, so every disaster has trauma. But there’s something uniquely nightmarish about earthquakes– not that it’s worse than something else, but it’s just a very– for example, a hurricane, you can see coming. You can even forecast these things.

A volcano can explode without warning. But almost all volcanoes give out some warning. They change shape. They heat up. They give off a certain kind of gas. They kind of splutter. And you get earthquakes, symbolizing the movement of magma.

Even a tsunami goes rushing across the ocean. It takes long enough now that with modern early warning networks, people can actually do something about it. An earthquake is almost like it’s everywhere all at once around you. Everything you take for granted, that you think is a permanent structure, from roads to buildings, entire neighborhoods just vanish.

And the only thing I can think that compares to is a nuclear bomb, really. It’s like a giant kind of explosion of energy. The physics are quite different, but it feels deific, somehow. Even with all the science of understanding how earthquakes work, when an entire city or entire villages can just be disappeared with no advance warning, crucially, it just feels particularly nightmarish, really. That’s just terror and horror.

IRA FLATOW: You talked about the frustration of not understanding yet how to determine whether an earthquake can happen. Tell me about where we stand in that effort to try to predict earthquakes.

ROBIN GEORGE ANDREWS: Yeah, so we stand– or rather, the earthquake scientists– I wouldn’t say they’re at square one. But in terms of prediction, prediction requires three things. You need to know exactly where an earthquake is going to happen next. You need to know how powerful that will be. And you need to know exactly when it will happen. That’s what defines earthquake prediction.

And it’s currently impossible. There’s not even, like, a famous paper where seismologists and geophysicists got together and they’re like, oh, we think we’ve found a precursor for all earthquakes. And then they tested it, and it didn’t quite work. Even that has not happened kind of thing.

It’s really difficult to find precursors. So much of the science is kind of retrospective. And even if scientists understand, OK, this fault has a high seismic hazard because it hasn’t ruptured in 400 years, and they can measure the amount of pressure, essentially, the tension building up on a fault– you can actually measure these things. But that doesn’t give you any way to say, in 10 days’ time, it will make the slip.

The best scientists can do in some parts of the world is probabilistic forecasting. That’s when you say, for example, the San Andreas Fault, the USGS say there’s a relatively high chance– I can’t remember the exact number, but it’s a relatively high chance in the next 30 years or so, either San Francisco Bay Area or the Los Angeles area is going to experience a relatively powerful earthquake.

But it’s not clear how reliable those kind of forecasts are. And even if they are, what are you supposed to do about that, apart from make sure your building codes are up to date, and make sure people have got their drop, cover, and hold on practice, really? I mean, that’s important. But without knowing what the precursor signs for a major earthquake are, they always bring about ruin.

IRA FLATOW: Yeah, but that’s pretty important, as you say, because if you did have the right kinds of buildings, perhaps you wouldn’t have such devastation like we’re seeing now.

ROBIN GEORGE ANDREWS: Yeah, and each situation is different, right? So parts of the West Coast in the US have pretty good building regulations. I mean, it’s a bit patchworky, but it’s better than a lot of places in the world. Like, Japan’s pretty good on this.

As we saw in Turkey, Turkey was almost the polar opposite of that. Not only were a lot of buildings in the affected regions not fitted or retrofitted for earthquake resistance, but systemic corruption in the construction industry and the increasingly authoritarian government meant that money and effort that was supposed to go towards making sure these buildings were earthquake resistant was not used kind of thing. So often, the death toll is a lot higher than it needs to be because of building codes.

But as you can see in the Morocco case, it’s quite complicated. Like, in Marrakesh, it would be a lot easier to have a local government go, OK, we’re going to make sure all buildings, even in the old part of the city, are going to be fitted to withstand earthquakes. But what do you do with scattered villages in the mountains? Like, that’s a much bigger logistical headache to get around. It’s not impossible, but there’s no perfect scenario, basically, for this.

IRA FLATOW: This is Science Friday from WNYC Studios. In case you’re just joining us, we’re talking about the science of earthquakes. Well, if you’re building a building from scratch, how do you make it earthquake-resistant?

ROBIN GEORGE ANDREWS: So one of the ways is, you make sure it sways with the motion of the ground. So earthquakes make the ground move, broadly, in two ways. They make the ground move up and down, which doesn’t help.

But the side to side motion is really problematic. I mean, that’s the sort of thing that can tear buildings apart. And then you get some seismic waves that cause other kind of vibrations. So it’s hard to plan for all scenarios. But making sure it moves with the motion of the quake helps.

An example of a lot of the problems in Turkey is, a lot of apartment buildings, building contractors saved costs by– instead of having a really strong foundational base, like with really rigid pillars at the base of these buildings, they put a [? shop ?] in. And that required knocking out a few of the kind of foundation pillars. So when the earthquake happened, the buildings just pancaked down on themselves because of that kind of thing.

So to actually make a building earthquake-resistant is complicated, but it’s not so complicated that it can’t be done if governments and, in some cases, private companies are willing to invest in doing it. It’s basically a question of what cost saving is worth the risk of losing a human life kind of thing. And I think many people would argue that no cost would be too high.

IRA FLATOW: With the rise of AI and now all these other artificial intelligence technologies, do you think that AI might help predict earthquakes or alert people sooner?

ROBIN GEORGE ANDREWS: So what AI is particularly good at is pattern recognition. It can do it tirelessly. And it’s much better than humans at that kind of thing.

So AI is already being used in seismology. It’s tentatively being used in forecasting efforts. But really, the main use right now is to map out fault networks in absolutely stunning resolution. And it does that by essentially listening to the entire sum of the seismic noise coming out of, for example, California. And there’s a lot of seismic noise in California, not just from earthquakes, but from traffic, from people walking about, from Taylor Swift gigs. A lot of noise happens.

And what these networks do is, they train themselves on what is an earthquake and what isn’t. And they are finding millions and millions of really imperceptibly small earthquakes that kind of light up hidden fault lines like a flare. So really, the strongest use I’ve seen in this field is to help scientists work out where all of the faults are, including ones that may not have moved for a long time, so are harder to detect, exactly like the ones in Morocco.

So I think it’s a promising thing. But it’s not going to be a panacea, I don’t think, for earthquake forecasting. That will require some sort of scientific revelation.

IRA FLATOW: In the couple of minutes I have left, let’s talk about how do you protect yourself if you feel there’s an earthquake coming or you live in an earthquake-prone neighborhood.

ROBIN GEORGE ANDREWS: Right. So the advice does vary in different parts of the world because of things like building codes. But on the West Coast and broadly speaking, the best advice is to drop, cover, and hold on. So that means you feel shaking. Even if you’re not sure how powerful the earthquake’s going to be, you drop to the floor. And you go under something that’s relatively rigid, like a strong table, or some sort of alcove, or something that would shield your head from falling debris. You then hold on and wait until the shaking stops. Like, sometimes, you might think the earthquake’s over, but it’s not. So you have to kind of be patient with it.

So broadly speaking, that’s the best advice. But the other thing I would say is, especially if you live in the West Coast, is download apps or make sure your phone is able to get alerts from the US Geological Survey’s ShakeAlert System. But basically what it does is, there are seismometers all over the West Coast. And if enough of them detect an earthquake, and their autonomous systems quickly process that, and it’s above a certain magnitude, it will warn people in the area, an earthquake is coming. You’d better get to cover.

And that may sound like you wouldn’t have any time at all. But the speed of telecommunications is the speed of light. And that’s faster than the speed of seismic waves, even though they’re really, really fast. So if you live 50 miles away from the epicenter, it may give you a valuable 5, 6, 7-second lead, which could save your life.

IRA FLATOW: Robin, I want to thank you for sharing your reporting with us. Very informative.

ROBIN GEORGE ANDREWS: You’re very welcome. Anything to help.

IRA FLATOW: Dr. Robin George Andrews, volcanologist and science journalist based in the UK. And our thoughts go out to the victims in Morocco.

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