Chile's Buckling Part Of Earthquake Belt

Chile's 8.8 magnitude earthquake occurred on one of the most seismically active areas of the planet. In fact, the largest earthquake ever measured stuck not far away, back in 1960. It was a magnitude 9.5. It, too, spawned a tsunami that swept across the Pacific.

  • Chilean troops and firefighters unload relief supplies Wednesday from a military helicopter in the coastal town of Dichato, which was heavily damaged by tsunami waves produced by Saturday's 8.8-magnitude earthquake.
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    Chilean troops and firefighters unload relief supplies Wednesday from a military helicopter in the coastal town of Dichato, which was heavily damaged by tsunami waves produced by Saturday's 8.8-magnitude earthquake.
    Ricardo Mazalan/AP
  • A policeman stands near medicine and other items donated Wednesday for earthquake victims.
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    A policeman stands near medicine and other items donated Wednesday for earthquake victims.
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  • A woman washes her hands at a makeshift shelter for displaced people in the seaside town of Constitucion on Tuesday.
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    A woman washes her hands at a makeshift shelter for displaced people in the seaside town of Constitucion on Tuesday.
    Fernando Vergara/AP
  • Secretary of State Hillary Clinton is greeted by Chilean President Michelle Bachelet at the airport in the capital, Santiago, on Tuesday.
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    Secretary of State Hillary Clinton is greeted by Chilean President Michelle Bachelet at the airport in the capital, Santiago, on Tuesday.
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  • Chilean army armored personnel carriers drive along a bridge Tuesday in Concepcion, the country's second-largest city. Bachelet said Chile has dispatched 14,000 to devestated areas.
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    Chilean army armored personnel carriers drive along a bridge Tuesday in Concepcion, the country's second-largest city. Bachelet said Chile has dispatched 14,000 to devestated areas.
    Daniel Garcia/AFP/Getty Images
  • People wait for supplies in front of a supermarket in Concepcion.
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    People wait for supplies in front of a supermarket in Concepcion.
    Aliosha Marquez/AP
  • Police arrest a woman who was carrying goods out of a supermarket in Concepcion.
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    Police arrest a woman who was carrying goods out of a supermarket in Concepcion.
    Mario Quilodran/El Mercurio/AP
  • Rescue workers help an injured woman in Concepcion.
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    Rescue workers help an injured woman in Concepcion.
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  • A man holds a child outside a quake-damaged building in Concepcion early on Saturday.
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    A man holds a child outside a quake-damaged building in Concepcion early on Saturday.
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  • A boat rests next to a building Monday after it was washed ashore by the tsunami in Talcahuano.
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    A boat rests next to a building Monday after it was washed ashore by the tsunami in Talcahuano.
    Daniel Garcia/AFP/Getty Images
  • Throughout central Chile, travelers faced obstacles. Here, a collapsed bridge across the Claro river, about 112 miles south of Santiago.
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    Throughout central Chile, travelers faced obstacles. Here, a collapsed bridge across the Claro river, about 112 miles south of Santiago.
    Aliosha Marquez/AP
  • Smoke from a burning building fills the sky on the outskirts of Santiago.
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    Smoke from a burning building fills the sky on the outskirts of Santiago.
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  • Firemen search for survivors in a destroyed building in Concepcion on Sunday.
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    Firemen search for survivors in a destroyed building in Concepcion on Sunday.
    Natacha Pisarenko/AP
  • People in Concepcion stand outside guarding their homes on Monday.
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    People in Concepcion stand outside guarding their homes on Monday.
    Natacha Pisarenko/AP
  • A man holds a torn and soiled Chilean flag on Sunday in a flooded area of Pelluhue, about 200 miles southwest of Santiago.
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    A man holds a torn and soiled Chilean flag on Sunday in a flooded area of Pelluhue, about 200 miles southwest of Santiago.
    Roberto Candia/AP
  • Bejamira Neira Zapata sits in the doorway of her house Monday after the massive earthquake struck the village of Penco. The tsunami engulfed the normally placid Penco and neighboring villages.
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    Bejamira Neira Zapata sits in the doorway of her house Monday after the massive earthquake struck the village of Penco. The tsunami engulfed the normally placid Penco and neighboring villages.
    Evaristo Sa/AFP/Getty Images
  • Concepcion, about 70 miles from the epicenter, suffered some of the worst damage.
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    Concepcion, about 70 miles from the epicenter, suffered some of the worst damage.
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  • Following one of the largest earthquakes ever recorded, a woman stands in front of a destroyed home in Pelluhue.
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    Following one of the largest earthquakes ever recorded, a woman stands in front of a destroyed home in Pelluhue.
    Roberto Candia/AP

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Big earthquakes are usually caused by events that occur on a truly planetary scale — that is, giant chunks of the Earth's crust — tectonic plates — that are slowly moving around. Seismologist Kate Hutton at Caltech says the coast of Chile is the perfect example.

"It's very seismically active because it's like California," she says. "It's on the boundary between two of the Earth's major tectonic plates. In this case, it's the Nazca plate and the South American plate."

The Nazca plate is moving east at the rate of about 3 inches a year. Since South America is already sitting to its east, the plate has nowhere to go but down. It plows beneath the South American plate. Over geologic time, the result is obvious.

"The deformation is causing an ocean trench — a very deep area offshore — and very high mountains, the Andes Mountains, with the volcanoes and everything on shore," Hutton says. In the short term, though, strain simply builds up in the rock.

"When it finally does break, there's a lot of stored energy within the deformed crust that can be released as an earthquake," she says.

In this case, not just an earthquake, but a tsunami — that sharp jolt underwater kicks up a wave.

"It's sort of like sloshing in the bathtub," Hutton says. "If it's a big enough earthquake, then the waves that are caused on the ocean will travel all the way around the Pacific."

This head-on collision of tectonic plates in Chile has been responsible for 13 quakes of magnitude 7.0 or higher since 1973, according to the U.S. Geological Survey. Still, this weekend's quake ranks among the strongest on record.

"There were only three earthquakes in the 20th century that were bigger than this earthquake," says Brian Atwater, who works for the USGS out of the University of Washington.

"Those three earthquakes were in Kamchatka in 1952, in Chile in 1960 and in Alaska in 1964."

Of course, there was another giant quake in 2004, the Indonesian quake that triggered the devastating tsunami. These are very rare events.

By comparison, the quake that devastated Haiti last month was a comparatively modest 7.0. The Chilean 8.8 released 500 times as much energy. So why was the Haiti quake so much more deadly? For one thing, the epicenter was much closer to a densely populated area. Atwater says it's also that the quake was surprisingly compact.

"Nearly all the energy from the Haitian earthquake came from a patch just ... 5 or 10 miles long," he says. "So it's very, very concentrated."

The Chilean quake, by comparison, caused a large area of ground to slip. Atwater says not to think of a dotlike epicenter in this case. Instead, think of a failure zone shaped like a giant sausage, 70 miles away from the nearest significant city.

Also, in Haiti the buildings that collapsed were poorly constructed to begin with. Unlike Chile, people there didn't have experience building for earthquakes. Besides, Hutton says, Chilean buildings haven't just been built better, they've been put to the test.

"Probably most of the really vulnerable buildings have already been destroyed in earthquakes," she says.

Of course, a quake of this size still causes lethal damage, spread over a large area. But it made a big difference that Chile knew something like this was inevitable, and made an effort to be prepared.

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