Chile quake called a ‘megathrust’

  • Sat Feb 27th, 2010 10:32pm
  • News

By Alicia Chang Associated Press

LOS ANGELES — The huge earthquake that struck off the coast of Chile belongs to an “elite class” of mega earthquakes, experts said, and is similar to the 2004 Indian Ocean temblor that triggered deadly tsunami waves.

The magnitude-8.8 quake was a type called a “mega- thrust,” considered the most powerful earthquake on the planet. Megathrusts occur when one tectonic plate dives beneath another.

That type of action gave rise to the Andes mountains that form the backbone of South America, and is the source of some of the largest quakes.

Saturday’s tremor unleashed about 50 gigatons of energy and broke about 340 miles of the fault zone, according to the U.S. Geological Survey’s National Earthquake Information Center.

The quake’s epicenter was offshore and occurred about 140 miles north of the largest earthquake ever recorded — a magnitude-9.5 that killed about 1,600 people in Chile and scores of others in the Pacific in 1960.

“It’s part of an elite class of giant earthquakes,” said USGS geologist Brian Atwater.

If the magnitude holds, it will tie with the 1906 offshore Ecuador quake as the fifth largest since 1900.

“We call them great earthquakes. Everybody else calls them horrible,” said USGS geophysicist Ken Hudnut. “There’s only a few in this league.”

The Chile quake was smaller than the Sumatra quake of 2004, a magnitude-9.1, and was not expected to be anything nearly as destructive. That quake and ensuing tsunami killed 230,000 people.

Another difference is that the Chile quake triggered tsunami warnings hours ahead of time in Hawaii and Pacific islands, allowing people time to flee to higher ground, an action that turned out to be unnecessary after all.

In 2004, there was little measuring technology in place to warn Indian Ocean countries about incoming killer waves.