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Seabed shows impact of quake

Huge 'scars' seen in first pictures of Indian Ocean

BANDA ACEH, Indonesia -- The first images yesterday of the seabed battered by the earthquake that triggered Asia's catastrophic tsunami revealed huge ruptures spanning several miles.

A British naval ship collecting data off the coast of Indonesia's Sumatra Island produced the digital images using sonar, and they could be used to help develop a tsunami early-warning system for the Indian Ocean region.

The vibrantly colored seabed maps show the 9.0-magnitude quake caused the tectonic plates to clash ''like the rumpling up of a carpet," according to Steve Malcolm, commanding officer of the HMS Scott. The images show ''scars" more than 6 miles wide resulting from the Dec. 26 quake. They depict the line where the Indian tectonic plate suddenly collided with, and was pushed underneath, the Burma plate.

The maps, created with multibeam sonar, show ridges as tall as 4,950 feet that were created over thousands of years by the slow collision of the deep, flat Indian plate and the ragged edge of the Burma plate. That collision has resulted in the Indian plate being gradually shoved under the edge of the Burma plate in a process known as subduction, said Russell Wynn, a marine geologist at the Southampton Oceanography Centre, which took part in the survey.

The Dec. 26 quake was caused by a sudden movement of the two plates, which in turn caused the ridge of the Burma plate to spring up about 30 to 60 feet, Wynn said. That sent water surging up and out, creating the devastating waves that menaced the region. More than 160,000 people in 11 Indian Ocean nations were killed.

Wynn said scars seen on the digital images were probably landslides created by sediment being loosened by the earthquake. The epicenter of the earthquake was 24 miles below the seafloor, Wynn said.

Scientists from the Southampton Oceanography Centre in southern England and the British Geological Survey have been working with the crew on the HMS Scott since Jan. 26.

The images show deep areas in dark purple and blue, and the high ridges caused by the slow plate collision in green, yellow, and red. The images were on display at the United Kingdom Hydrographic Office in Taunton, southwest England, and on the body's official website.

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