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 "megathrust," considered the most powerful earthquake on the planet. Megathrusts occur when one tectonic plate dives beneath another. Saturday's tremor unleashed about 50 gigatons of energy and broke about 250 miles of the fault zone, said U.S. Geological Survey geophysicist Paul Caruso.

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.