By Sid Perkins
The magnitude 9.0 earthquake that struck the ocean bottom west of Indonesia on the morning of Dec. 26, 2004, triggered several tsunamis that killed an estimated 145,000 coastal residents and tourists, claiming lives on shores even thousands of kilometers away. Researchers are now analyzing the events that led up to the destruction and modeling their possible long-term effects.
The largest temblor in 40 years occurred along a subduction zone where the immense fragment of Earth’s crust known as the India plate is forced beneath the Burma plate at an average rate of 6 centimeters per year. Analyses of seismic vibrations produced by the quake place its epicenter just north of the island of Simeulue, which lies about 150 kilometers off the western coast of Sumatra. From there, at a depth of 18 km, the rupture raced northwest at supersonic speeds for more than 200 seconds, says Chen Ji, a seismologist at the California Institute of Technology in Pasadena.
In all, slippage occurred along about 1,200 km of the interface between the tectonic plates—a distance that would span California from north to south with about 100 km to spare. At some spots along the interface, one plate may have slid as much as 20 meters past the other, says Ji.