Why Can’t We Predict Earthquakes?

The Tohoku earthquake off the Japanese coast on March 11^th measured 9.0 on the Richter scale. That’s the fourth-biggest recorded earthquake in the world since 1900, the worst in Japan since modern instruments were first used 130 years ago. The earthquake and the tsunami it triggered led to shocking damage – loss of life, loss of property, all sorts of aftermath issues. But as shocking as the damage has been, the earthquake itself wasn’t all that surprising. Seismologists — the scientists who study earthquakes – they know a great deal about where they’re likely to occur, and how serious they’re likely to be.

The fact is that, according to the USGS — that’s the United States Geological Survey — several million earthquakes happen around the world every year. Only a select few make us sit up and take notice. Japan, unfortunately, is one of the places where those select few tend to occur.

So how good are we at predicting the next big earthquake? How good are we at prediction in general? That’s the theme of an hour-long special we’re producing right now, to air later this year on public-radio stations. Predicting the future is almost impossible; that said, human beings are practically addicted to prediction. With something as serious as earthquakes, you can’t blame them …

That’s what the Japanese earthquake sounded like, as recorded beneath the ocean’s surface by Japan’s Agency for Marine-Earth Science and Technology.

Back in the fall, I visited the U.S.G.S. office in Menlo Park, California. It sits just a few miles from the San Andreas Fault, the most serious earthquake threat in this country. At the time, the most recent earthquakes in memory had been in Haiti and Chile, not in Japan. I wanted to talk to a geophysicist about earthquake prediction. I knew they had a machine there, in the lab …

DUBNER: Okay, so describe just where we are.

Bill ELLSWORTH: So we’re in one of the laboratories where we have a very large machine that simulates earthquakes. Now this particular apparatus does something very interesting.  It starts sliding slowly, initially in a small spot, and that slow sliding will grow to a critical size until [popping sound] an earthquake happens.

That sound you heard [popping sound], that was actually the sound of the scientist slapping his hand on the machine. The real sound the machine makes is about like this … [ambient sound]. So I’ve got to admit, when I first heard about the USGS’s “earthquake simulator,” I envisioned something a little more dramatic. Some kind of an amusement-park ride, or something. But it’s just a metal frame, a few yards across, with a big slab of rock inside, and the frame is compressed by hydraulic pressure. The “earthquake” it simulates then is vanishingly small.

But still, how does this sound [ambient sound] translate into that [tape of Japanese earthquake ]? And how can that knowledge be used to predict the next Big One — whether it’s in Japan, in Chile, or in California?

*      *      *

Meet the scientist who was good enough to talk me through the science of earthquake prediction.

ELLSWORTH: My name is Bill Ellsworth, and I’m a geophysicist at the U.S. Geological survey.”

Ellsworth is a genial guy, low-key and soft-spoken, in his sixties, with eyeglasses and a trim white beard. Bald on top. He looks like a guy who’s very comfortable spending long days in the lab, digging into the earthquake data. But I wanted to know if he’d ever experienced a real quake.

ELLSWORTH: The most exciting earthquake I’ve been in was the 1989 Loma Prieta earthquake.  And it was at the end of the workday.  And I was closing down my computer, going home to enjoy the World Series, when I felt something that I’d never experienced before.  It was a very low frequency wave, but a very large amplitude. Large enough that you’d know something was going on.  And I fortunately guessed that this was the P-wave, or the fast-running wave, of an earthquake, and that the S-wave, the strong shaking wave, was to come later.  So I immediately got up, moved to the door frame in my office, braced myself there, and rode through the sheer wave, which shook the building hard enough that you could hear things wracking and moving. You could hear the beams shaking. You could hear things falling. Um, as soon as the shaking had stopped, the lights were out, since we had lost electrical power throughout the region. Which meant that the high tech digital telephones were dead. I walked down the hall, where I knew there was an old fashioned analog telephone and called my colleagues at the USGS headquarters back in western Virginia, who were also getting ready to enjoy the ball game and said, “Our world has just changed.”  And indeed, it had.

DUBNER: I see you’re wearing a wedding ring.  You’re married now, I guess.  Were you married then?

ELLSWORTH: I was indeed.

DUBNER: But the fact is that after the earthquake hit here, your first phone call was to your USGS seismology colleagues, not to your wife.  Is this true?

ELLSWORTH: It is true.  She knew that when the earthquake hit some day, that she wasn’t going to see me for a while.  But I did contact her shortly thereafter and things were fine at home.

DUBNER: But that’s what happens when you marry a seismologist and you live in Northern California, right?

ELLSWORTH: I’m afraid so.

Ellsworth and his wife were all right after the Loma Prieta earthquake or, as some people remember it, the World Series earthquake. It hit 6.9 on the Richter scale, killed 63 people in northern California. The official death toll from the Japanese earthquake has already passed 9,000, and will likely go much higher. There are all kinds of reasons to want to know as much as possible about the next big earthquake, to be able to predict as much as you can, as accurately as you can. So that’s what I asked Ellsworth about …

DUBNER: Where does the word prediction fall into this?

ELLSWORTH: Well, we’re interested in predicting three things about earthquakes: one is, “Where will they occur?” The second is, “How strong will they shake the ground when they do occur?” And the third question is, “When will they occur?”  The first two are in pretty good shape actually.  The third one is the really tough problem.

DUBNER: And I’m guessing when you go to friend’s house, there’s a cocktail party, a barbecue, is that what they want to know from you, is it, “Bill, when is the Big One and how do I get out of here?”

ELLSWORTH: That’s usually the question they ask.  And my response is usually, “That’s a little bit like asking should I be buckling up my seatbelt in my car just before the accident?”  Better to put it on ahead of time and better to be planning for how to drive safely and not worry about when something bad might happen. If you’re prepared, you’ll get through the event okay.

DUBNER: Do you feel that there’s too much emphasis or too much attention paid to the prediction part of what you do?

ELLSWORTH: You know, it’s always a very popular topic.  Since no one knows how to predict earthquakes, it’s kind of an open field.  And people with all sorts of interesting ideas like to get involved.  We were, I think, quite optimistic at the beginning of the program that prediction was something we could do through our understanding of the basic mechanics.  And as time has gone by, I think we’ve been sobered by what we’ve seen.  That if earthquakes are predictable, we don’t yet know how to do it.  And there’s a good chance that they’re not predictable.

DUBNER: Talk a minute about the belief among certain people that they are very good at predicting earthquakes.

ELLSWORTH: I think there are many people who have the belief that they can predict earthquakes, and the real question is, “Can you show that you made a prediction before the fact?” and that that prediction can be tested in a scientific manner.  We can certainly say that there is going to be a magnitude five earthquake in the world somewhere today.  That’s an easy prediction.  We can probably say that there’s going to be a magnitude six earthquake in California in the next 100 years.  That’s a gimme.  But in terms of making a prediction that’s really testable, that’s a much harder thing to do.  One of the very interesting things that was done years ago, this was back in the days of telephone answering machines.  We had a project that had a group of volunteers.  People who had animals that were very sensitive to the coming of earthquakes.  And the instructions were that when their animals acted up, they were to call the number and leave a message.  There were never any messages left before earthquakes.  But lots of messages left after earthquakes.  Oh, they had meant to call, but they didn’t.

DUBNER: So in other words, “Moments before the earthquake, I noticed that my cat was pacing back and forth.”

ELLSWORTH: That’s the kind of thing.  Exactly, yeah.

DUBNER: We are speaking here at the USGS offices at Menlo Park, California.  Which is how far from the San Andreas Fault lines?

ELLSWORTH: San Andreas is about six or seven miles up the hill from us here.  So we’re living in earthquake country, definitely.  We estimate that in the next 30 years, there is a better than two to one chance that we’re going to be hit by a fairly major earthquake like the one that hit in 1989.

DUBNER: And where do you live?

ELLSWORTH: I live here in Menlo Park.

DUBNER: So you live a few miles from the San Andreas Fault line and a little bit further maybe from a few others.  Does it keep you up at night?

ELLSWORTH: It doesn’t keep me up at night.  My house is 60 years old or so and likely will have some damage if an earthquake strikes.  I don’t think it has any chance of collapsing.  So I think we’ll get through the earthquake okay.  But it’s a hazard that I feel I can live with.

DUBNER: You say that the odds that a serious earthquake will hit this area where we’re sitting now by 2040 are significant, damages would be significant, potentially loss of life significant.  Yes, we are agreed on that?

ELLSWORTH: We are agreed on that.  We made some estimates based on the repeat of a big earthquake on the Heyward fault, and that would be really a very serious event.  We’d be talking about many tens, if not hundreds of billions of dollars in losses.

DUBNER: Do you ever just say, “Why the heck do people live in obvious potential harm’s way?”  So we see with hurricanes that people have been flocking in millions to places where hurricanes happen a lot.  California, which has probably more earthquake danger than any other state, I’m guessing, per mile, per capita, would that be true?

ELLSWORTH: We have the most exposure, in terms of people who are exposed to earthquakes.  We have earthquakes that are just as severe in many, many other states.  Perhaps what we have done a better job of in the West is adopting the codes that are necessary for structures to survive earthquakes.  I could draw a parallel perhaps between two earthquakes that happened this year with very, very different effects.  Neither were within the US, but this past September, there was a magnitude seven earthquake just outside the city of Christchurch in New Zealand.  And this earthquake did tremendous damage to chimneys and things within the city.  There were many older brick buildings that collapsed.  But fortunately it occurred in the middle of the night and there were no lives lost.  That earthquake is really no different in size and in severity than the one that hit Haiti in January.  And look at the difference there.  Engineering does work.

DUBNER: There are obviously big earthquakes and small earthquakes.  The big ones are the ones that people hear about, the ones that people care about.  How many earthquakes, however, are there in a given day around the world, let’s say?

ELLSWORTH: Well, we typically see an earthquake of magnitude six once a week, globally.  And the way that earthquakes work, if you have one magnitude six, you’ll probably have ten magnitude fives, and you’ll have a hundred magnitude fours, and a thousand magnitude threes, and it just goes on and on down the Richter scale.  So in a sense, the earth has organized itself in an interesting way — that the worst it does is in the biggest earthquake, but those are the rarest ones.  So instead of being peppered with damaging ones everyday, we get the “Big One” once a century.

Coming up, what small earthquakes can tell us about “The Big One,” and what geophysicists think of the public’s understanding — and misunderstanding — of earthquake predictions.

*      *      *

DUBNER: We’re in California, where big earthquakes have happened and caused real damage, in recent years and in faraway years.  So talk to me a bit about what the future looks like here and how scared we should be.

ELLSWORTH: Um, unlike the atmosphere, which say, meteorologists work with, we can’t see underground.  And also unlike the meteorological situation, we don’t have satellites that allow us to map the system.  We don’t even really know the equations that govern the way that earthquakes work.  And it turns out that the small earthquakes are one of the most important things that we can gather. They actually allow us to map out in space where the faults are.  And from that we can actually begin to build these physical models that hopefully will lead to more accurate predictions in the future.

DUBNER: But did you just say, did you just say that you don’t really understand the equations that describe the way earthquakes work?

ELLSWORTH: That is correct.  We have—

DUBNER: I was starting to feel safer around you, and all of the sudden—

ELLSWORTH: Well, we know a lot about how seismic waves propagate in the earth.  That we understand.  But what actually happens on the fault the moment when the earthquake starts, what leads up to the occurrence of the earthquake, and how does that propagate, we’ve got some good models, but we don’t have any other real samples of faults that are active today.  So science moves forward by people putting something on the line, and then you have to see what happens.  If your prediction is correct, it doesn’t mean your theory is correct.  It means that it’s possible.  If your prediction is wrong, then it tells you something is wrong with your theory.  What people don’t remember about science is you can’t prove that something is true, but you can prove that it’s false.  So we’re always working in this duality of trying to build better theories, better models, that can explain the natural world, but knowing that ultimately they’re going to fail some test.  The good models work well.  The bad models go away in a hurry.

DUBNER: Should I move here?  Will there be an earthquake here?  My children are 8 and 10.  Will there be an earthquake here in their lifetime that is potentially devastating to us?

ELLSWORTH: There’s certainly a good chance there would be an earthquake, but there’s really no reason not to move here.  Public schools are one the safest places to be for your children.

DUBNER: Oh, so you’re saying that it’s okay they’re in school, but I’m worried about them being—on the weekend I’m worried, though.

ELLSWORTH: So, on the weekend, you need to think through what your hazard is.  You should probably look at the house you live in as well and decide, “Is this one that’s earthquake safe?  Do I have things that are going to fall down and injure someone in bed?”  You spend a third of your life in the bed.  Make sure nothing’s going to fall on you there and kill you.  Have a plan.  These are the kind of things that we remind people to do.  And if you take those very sensible steps, the earthquake problem is not going to be the most severe thing that you have to experience in your lifetime.

DUBNER: What is that?

ELLSWORTH:I wish I knew, but it won’t be that.

DUBNER: What did people used to think caused earthquakes?

ELLSWORTH: The Greeks thought they were related to gases escaping from the earth.  Of course, in Japan, the tradition is that the islands are riding on the back of a big catfish that shakes its tail from time to time.  But the scientific understanding of earthquakes really developed in the 19^th century when people began to collect systematic observations and realized that there was something that was mappable about the earthquake shaking.  And in a sense, rocks are a relatively simple system.  Everybody know they’re brittle.  If you strain them hard enough, they’re going to fracture.  But they’re also elastic.  That if you push on them, but not to the point of breaking, and then release the force, it’ll spring back.  And that’s exactly what happens in an earthquake: most of the rock is behaving elastically, except the inelastic part along the fault.  And it’s that inelastic part which is the challenge for us to understand.

DUBNER: So last year, there were a pair of very large earthquakes, one of which was wildly devastating in terms of property and life.  The other one somewhat so.  One in Haiti, one in Chile.  And it seemed as though much of the world thought there was an earthquake epidemic upon us.  Was there?  Is there such a thing?

ELLSWORTH: You know, we’ve looked at that question.  Were there an unusual number of large earthquakes, either this past year or the past decade?  And the answer is no.  That they’re all within statistical norms.  And it’s when we have a couple of events in a row that impact society that we hear about it.  There were bigger earthquakes that were out in the middle of the ocean that nobody had ever heard of.  So from a global perspective, we’re not looking at a kind of global earthquake cluster.

DUBNER: What has your work in seismology taught you about the human yearning for prediction in general?

ELLSWORTH: Well we love black and white answers, I think, and it’s very difficult for people to grapple with concepts of probability.  So if I say that there’s a 100% chance that the sun is going to rise tomorrow, people will be pretty confident that that’s going to happen.  But if you tell them that simply by commuting in their car today, they’ve increased their risk in dying today by a factor of 1000, as opposed to staying home, they have trouble grappling with that.  It certainly doesn’t freeze us out of our cars.  But it indicates to me that we have a long ways to go as human beings to understand low probability events and how to take effective and wise actions in the light of those.

There’s something weirdly satisfying about hearing an expert say, without reservations, that the future is impossible to predict.

In just about any realm you can think of – finance and politics, parenting — most experts will tell you they have all the answers  — about the past, the present, and the future. It barely matters that they’re often wrong — that they’re only right about as often as a monkey with a dartboard would be right. What matters is that our thirst for prediction is so severe that we’ll drink it up again and again and again.

But a scientist like Bill Ellsworth, even with all the data at his fingertips and all the computer modeling money can buy, he admits that predicting earthquakes to some degree… escapes him. I’ve got to say, I find some comfort in that admission. If the first step in dealing with a problem is admitting you have a problem, then maybe the first step toward predicting the future is admitting you can’t. Or something like that. You’ll hear a lot more on this topic this summer on Freakonomics Radio, on a public radio station near you — and at freakonomics.com.