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Chile earthquake, Hawaii tsunami: Why this happens

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IN PICTURES: Images from the 8.8 magnitude earthquake in Chile

Quakes are like a growth spurt

The squeeze one plate puts on the other as it slides back into the Earth’s mantle is building the Andes. When an event such as today’s quake occurs, it’s like a growth spurt, pushing the overlying crust up by several feet. That sudden displacement of mass underwater triggered the tsunamis that spread into the Pacific basin.

Today’s rupture occurred along a 248-mile length of a zone that traces the outline of most of South America’s west coast. The amount of slip was on the order of 30 feet, says Ray Russo, a University of Florida geophysicist whose research focuses on the region. He estimated that the crust closest to the epicenter may have experience uplift of three feet or more.

A more firm number will emerge after he and colleagues see GPS and radar-satellite data, he says.

Large earthquakes along the Nazca subduction zone – indeed along all of the earth’s subduction zones – are common. Globally, quakes with magnitudes comparable to today’s temblor occur on average once a year.

Since the 1970s, some 15 quakes in the magnitude 7 and 8 range have occurred along the Nazca’s subduction zone. The global-record holder occurred in 1960, when a magnitude 9.5 quake struck off the coast south of Conception.

Hard to predict when another quake will occur

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