Tracking The Geologic Impacts Of Earthquakes

The earthquake that shook Chile last weekend was powerful enough to push up the Andes a few feet, shift Earth's axis and even speed up the planet’s spin. Ross Stein, a geophysicist at the U.S. Geological Survey, explains the fallout of the quake and the physics that triggered it.

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IRA FLATOW, host:

This is SCIENCE FRIDAY from NPR. I'm Ira Flatow. Did you ever wonder where mountain ranges come from? How do they just appear? Well, last weekend's 8.8 magnitude earthquake rocked more than Chile's coastal cities.

Geophysicists estimate that the quake pushed up the Andes Mountains, pushed them up a few feet more. It also shifted the Earth's axis by about eight inches and shook up the planet's innards enough to change the speed of the Earth's rotation. Our days are about a microsecond shorter, according to one estimate. So if you feel tired, you can't get your work done, you know why: There's just not enough time left.

Up next, we'll talk about this quake and how it upset the whole balance of the Earth and reshaped it, and since then, there have been numerous other tremors around the world. There have been earthquakes in different places out there. Are they all related?

Our number, 1-800-989-8255. You can also tweet us, @scifri, that's @-S-C-F-R-I. And you can take a look at the shake map. We have a shake map of the Chilean earthquake on our Web site at sciencefriday.com.

Let me introduce my guest. Ross Stein is a geophysicist at the U.S. Geological Survey in Menlo Park, California. Welcome to SCIENCE FRIDAY.

Mr. ROSS STEIN (U.S. Geological Survey): Hi, Ira, glad to be here.

FLATOW: You're welcome. As I said in the last week, there have been major earthquakes. We've had them in Japan and Chile, Taiwan, following the one in Haiti. Are these all related in any way?

Mr. STEIN: We don't think so. Now, we could be wrong, and that happens, and I'm in a field where data trumps any kind of theory, but our understanding is that while the entire Pacific Ring of Fire is subject to earthquakes, the event in Haiti has only affected the Caribbean neighborhood, and the Chilean event has only affected the Andes and the trench that's off that coast.

FLATOW: Give us a little geology lesson in the Andes there. What was going on in the Chilean earthquake?

Mr. STEIN: Well, what we call the Nazca Plate, one of a dozen or so very thin pieces of the Earth's crust that are sliding around at speeds of a few inches a year is jamming its way into and under the Andean mountains. And so what's happening there is it is stuffing itself under the continent, and it does so in colossal earthquakes.

FLATOW: And it sort of pushes up. Every earthquake pushes up a little bit more of the mountain.

Mr. STEIN: That's right, and so in this earthquake we calculate that the coastline of Chile for three, 400 miles was uplifted several feet during this earthquake.

FLATOW: And does this shifting of mass around the world every time the Earth moves, does it make the Earth we heard about it wobbling. Is it that big an effect that it can actually affect the wobble of the Earth?

Mr. STEIN: Well, what's happening is that the denser material, the plate, what we call the Nazca Plate, the oceanic material which gets shoved underneath the continent because the continent is just a little less dense, you're basically jamming dense material deeper into the Earth, and just like a spinning skater that we watched during the Olympics, when she brings her arms in, she spins faster.

So that's the same phenomena, that you're just moving the density of the Earth a little closer to the center.

FLATOW: And we're also experiencing a period where we're seeing other masses move. I'm thinking about melting glaciers, right? They're forming pools of water. The ice is moving from one place to another. Could that also affect the Earth?

Mr. STEIN: Yes, it can. I mean, obviously that's not an earthquake-related phenomena, but as you melt glaciers, you actually put more of the water into the ocean, and then you also remove the load, and the land comes up because essentially the crust of the Earth is just like a slab of rubber over Silly Putty, and when you release, when you remove the mass above it, it'll start springing back, first quickly and then slowly.

FLATOW: What does it mean that this earthquake shifted the Earth's figure the axis eight centimeters? How did that happen?

Mr. STEIN: Well, it's just because we are not at the equator. We're down in the mid latitudes, the mid-southern latitudes, and so it causes the axis to shift slightly because we've changed the density structure of the Earth.

In fact, it's very, very easy with a gravimeter to measure when you've moved up a few inches that you're farther from the center of the Earth.

FLATOW: Let's talk about this Chilean earthquake and the 1960 earthquake. Could they be related, even though they're 40, 50 years apart?

Mr. STEIN: I think they're strongly related. First, the 1960 Chile earthquake is a magnitude 9.5. That's 20 times larger than the one we just had, and that's the largest earthquake ever recorded with seismic instruments.

So it is a colossus compared to the earthquake that we had on the 27th, and we calculated that that earthquake jacked up the stress at the site of the epicenter of this event by about a half a bar. That's about one-fifth or one-sixth of the pressure you put in car tires, and it seems to be enough in general to trigger seismicity.

FLATOW: And let's talk about the difference between a main shock, an aftershock, a foreshock. Are they all different phenomena or basically the same thing?

Mr. STEIN: No, this is the sham of seismology. They're all the same, and we just use these words after the event. So if we have some little earthquakes, and then we have a big one, in retrospect, we'll call those little earthquakes foreshocks. If we have a big one, and we get little ones afterwards, which we always do, we'll call them aftershocks.

But if I were to take, let's say a magnitude 5.4 shock of a big main shock, and a magnitude 5 aftershock of a big main shock and a magnitude 5 run-of-the-mill main shock, and I were to put them on a card table in Manhattan and ask someone as kind of a card Monte to tell me which one is which, there's not a seismologist on Earth who could tell them apart.

FLATOW: Wow, the sham of geology.

(Soundbite of laughter)

Mr. STEIN: So really, we don't know what marks a little earthquake for future greatness, and we don't know what really is a foreshock except looking backwards.

FLATOW: So give us an idea of perspective then. From a geology point of view, how do the Haiti and the Chile earthquakes compare in size and magnitude?

Mr. STEIN: Okay, if we think of if we represent an earthquake's magnitude by - or size - by the volume of a sphere, then imagine a ping-pong ball. That's Haiti. Now imagine a big high school globe. That's Chile.

FLATOW: Wow.

Mr. STEIN: So you could put 400 to 500 of those little ping-pong balls inside the big high school globe. So there is an enormous difference in the size of these events.

FLATOW: And so why were so many people killed in Haiti but not in Chile?

Mr. STEIN: Buildings. It's really staggering that when we try to remove the effect of the size of the earthquakes and say what percentage of people died who were subjected to severe shaking in both earthquakes, in Haiti it was eight percent. That not only means everybody knows somebody who died, everybody knows someone in their family who died.

Now, compare that to Chile. The number, the percentage of people who died, who were subjected to severe shaking, was .01 percent, and what that means is the buildings in Haiti were hundreds of times, maybe a thousand times, less safe.

FLATOW: Wow, wow. Let's talk about Charles Darwin, and I don't think people realize that he was actually around for another Chilean earthquake, right?

Mr. STEIN: Not only another Chilean earthquake, but the earthquake that occurred right where this one was. So he was on the Beagle in 1835. They felt the earthquake and he rowed ashore. And he got to shore and the first thing he noticed is that it stunk. He wrote in his journal that it was putrefying.

And he couldn't figure this out. Maybe it was gases. And then he began to see that all the marine inner-tidal life, all the little creatures there, were all dead, and that's why it stunk. And then he realized they were dead because these are creatures that get bathed by sea water twice a day, and they were all above sea level.

So he said, okay, there's only two possibilities here. Either the water level has dropped, or the land has risen. And he said: All the oceans are inner-connected. There's no real way to drop the ocean. So he said the land must have risen.

And that's breathtaking all by itself because at that time nobody thought earthquakes involved permanent movement of the land. They thought they were just underground explosions, and so he saw that this earthquake jacked up the coast several feet during this event.

FLATOW: Wow, so he was like the father of modern geology...

Mr. STEIN: It gets better.

FLATOW: I'm listening. Go ahead.

Mr. STEIN: And then he did what only Darwin could do. He stood there on the beach and he looked up at the 18,000-foot peak of the Andes, and he said, okay, that's how mountains are built. This mountain gets built by being jacked up several feet every several hundred years in earthquakes. And that's why Lord Byron plucked fossils out of limestone at the top of the Andes.

FLATOW: Wow.

Mr. STEIN: And it gets better still.

FLATOW: There's more?

Mr. STEIN: And then he goes: Okay, at the rate this happens, the Earth must be extremely old. It must be millions of years old. It requires eons to build 20,000-foot mountains out of jacking them up two feet at a time every several hundred years.

FLATOW: There's more, I'll bet.

Mr. STEIN: And so really, it's just a scandal that the biologists have absconded with Darwin's memories.

(Soundbite of laughter)

Mr. STEIN: He's ours. He's a geologist, and we're filing a class action suit.

(Soundbite of laughter)

FLATOW: I'll tell you, I never heard this story before. Is this a well-known story among geologists?

Mr. STEIN: It should be. And you know, it points out something else, which is that what makes geology unique is that that observation look, all he is he smelled and he looked. Something like that is out there waiting for all of us. It's right in front of our nose. It doesn't necessarily take complex instruments. That ability to see what's right in front of you and make these connections is something that makes it special and is available to everyone.

FLATOW: And that's the genius of a lot of scientists. They can look at the simple things and synthesize something totally new out of it.

Mr. STEIN: Yes.

FLATOW: Wow. Did he write much about this except that little observation?

Mr. STEIN: He did. He did write about it in "The Voyage of the Beagle," and Captain FitzRoy also wrote about it, the captain of the ship. So the and he did further investigations. He also saw that there were remains of Indian villages that had previously been at sea level and been jacked up by older earthquakes.

So he could see that when he looked back over kind of periods of 10,000 years or so that what had once been right on the water was now 10 or 12 feet up. So he saw the continuity of these observations all pointing to the ability of mountains being built by successive earthquakes. So if you see a mountain, you're looking at past earthquakes.

FLATOW: That's a great thought to end our conversation, and thank you for that Darwin. We're going to go read about the Beagle again and his recollection. Thank you, Ross.

Mr. STEIN: Okay, bye-bye.

FLATOW: You're welcome. Ross Stern(ph) is a geophysicist at the U.S. Geological Survey in Menlo Park, California. We're going to take a break, (unintelligible) Google through Darwin there and see what he wrote about the Beagle and the earthquake in Chile. Quite fascinating.

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