Peru Quake Kills Hundreds, But No Tsunami Threat

August 16, 2007

More than 450 people are reported dead after a massive quake rocked Peru yesterday, and officials expect the toll to rise.

But further devastation was spared because the magnitude 8.0 quake did not fracture the ocean floor and spawn a major tsunami, experts say.

Peru has a long history of deadly quakes and tsunamis due to its location near a subduction zone, the area where two tectonic plates meet, experts say. (How does an earthquake happen?)

In Peru, the Nazca oceanic plate slips beneath the westward-moving South American plate, located off South America's west coast. (Related: "Giant Earthquake Predictions Aided by Historical Data" [September 15, 2005].)

The two plates are converging at a rate of 3 inches (78 millimeters) a year.

"Typically the world's most damaging earthquakes occur when an oceanic plate slides under a continental plate, which is what happened in this case," said Joann M. Stock, a geophysicist at the California Institute of Technology in Pasadena.

Yesterday's quake originated near the source of two earthquakes of similar magnitude that occurred in 1908 and 1974, according to the U.S. Geological Survey (USGS).

"This earthquake occurred as thrust faulting on the interface between the two plates, with the South American plate moving up and seaward over the Nazca plate," David Wald, a USGS geophysicist, told National Geographic News.

The earthquake originated near the country's central coast, experts say.

The quake occurred at the boundary between the Nazca and South American tectonic plates, some 90 miles (145 kilometers) southeast of the capital, Lima, according to USGS. (See a Peru map.)

Tsunami Fears

Many experts feared the quake's immense burst of energy would spawn a tsunami.

The U.S. National Oceanic and Atmospheric Administration issued a tsunami warming for Hawaii yesterday that has since been canceled, according to the agency's website.

A small tsunami was detected yesterday, said USGS' Wald. Earthquakes of magnitude 8.0 have historically produced extensive tsunamis, he added.

Daniel Huaco, director of CERESIS, a seismology study group in Lima, said the earthquake's fracture wasn't large enough to reach the ocean floor, however.

"Had it broken the ocean floor there probably would have been a large tsunami," he said in a telephone interview with National Geographic News.

Wald agreed. "This one had its uplift mostly under the land and under shallow water," he said. "Had it been under deeper water or further out to sea, there might have been a bigger tsunami."

South America's west coast forms part of the circum-Pacific seismic belt, a 24,854-mile (40,000-kilometer) horseshoe-shaped alley of underwater trenches and volcanoes.

About 90 percent of the world's earthquakes occur along this belt, some experts say.

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