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Seabed shows tsunami scars

London, Feb. 10: These are the first images from a Royal Navy survey of the landslides, slumps and scars along 300 miles of seabed shaken by the earthquake that launched the devastating Indian Ocean tsunami.

The ocean survey vessel Scott studied the 'rupture zone' separating the two tectonic plates that clashed to create the magnitude 9.3 quake off the west coast of Indonesia. The results will aid understanding of earthquakes and help develop a tsunami warning system.

The depth of water in the zone west of Sumatra varies between 3,300ft and 16,500ft. Scott's high-resolution multi-beam sonar maps the sea floor by monitoring sound wave 'pings' bounced off the sea bed.

Scientists from Southampton Oceanography Centre and the British Geological Survey have been working with the Plymouth-based ship since January 26, one month after the tsunami claimed the lives of more than 250,000 people.

The earthquake occurred 20 miles below the sea floor where the Indo-Australian plate is colliding with the Eurasian plate. Movements of a few tens of yards of the seabed along the subduction zone of 750 miles created the pressure wave in the water column that became the tsunami.

The map of the seabed, displayed yesterday at the UK Hydrographic Office in Taunton, Somerset, showed the Indo-Australian plate ' marked in deep purple ' sliding under the Eurasian plate, causing the latter plate to bunch up to more shallow depths marked from blue, then green, yellow and red (most shallow).

Submarine ridges thrust up almost a mile and vast landslides left along 750 miles of seabed. The maps show the boundary between the deep, flat Indo-Australian plate, and the heavily deformed edge of the Eurasian plate. Scott's commanding officer Steve Malcolm likened distortion to 'the crumpling up of a carpet'.

The collision forced up spectacular large thrust ridges, almost a mile high. These unstable blocks have collapsed in places, producing large landslides several miles across. The survey also found a large landslide block some 300ft high and more than a mile down, and a diverted canyon.

Commander Malcolm said features appeared to be those of 'an absolutely enormous event in global terms'.

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