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Chile earthquake, Hawaii tsunami: Why this happens

The earthquake in Chile is a reminder of the lively geological activity under Earth's surface.

By Peter N. SpottsStaff writer / February 27, 2010

A Santiago apartment block shows major damage after Saturday's 8.8 magnitude earthquake in Chile. The quake earthquake and the Hawaii tsunami warnings it spawned are just reminders that our Earth is always moving.

Marco Fredes/Reuters

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The great earthquake that struck off the Chilean coast early Saturday serves as a stark reminder that the most violent earthquakes Earth’s restless crust can deliver happen along geological features that also appear along the Aleutian Islands, off the Pacific Northwest, and in the Caribbean.

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“We have the threat of this kind of earthquake and tsunami in our back yards,” says Brian Atwater, a geophysicist at the University of Washington in Seattle.

The magnitude 8.8 quake that hit Chile some 70 miles northeast of the coastal city of Concepcion resulted from action along what earth scientists call a subduction zone. A vast plate of oceanic crust known as the Nazca plate is sliding at a relatively speedy clip beneath the more buoyant continental crust of South America.

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