Magazine article Science News

Tsunami Disaster: Scientists Model the Big Quake and Its Consequences

Magazine article Science News

Tsunami Disaster: Scientists Model the Big Quake and Its Consequences

Article excerpt

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.

In the most-affected region, a broad expanse of seafloor--and thus the sea above it--was abruptly thrust upward as much as 5 m. The waves spilling away from that sudden bump raced across the Indian Ocean at jetliner speeds, says Ji. The first tsunami may have been 15 m high when it slammed into Sumatran shores about 15 minutes after the quake.

Satellite photos taken after the disaster indicate that the tsunamis deposited beach sand and soil or stripped away vegetation as much as 3 km inland along much of Sumatra's western coast. As of press time, the death toll in Sumatra was estimated to be in excess of 94,000. …

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