The Hindu : International : Ocean floor images offer tsunami clues

Online edition of India's National Newspaper
Friday, Feb 11, 2005

International

International

Ocean floor images offer tsunami clues

By David Adam and John Aglionby

By David Adam and

John Aglionby

LONDON/JAKARTA, FEB. 10. The first images of the seabed at the focus of the massive earthquake that caused the December 26 tsunami were released yesterday by scientists working on the British Royal Navy survey ship HMS Scott.

Though it is too early for experts to be sure what generated the Indian Ocean waves, the images have given them important clues. The sonar images show a section of the ruptured fault about 43 to 50 miles long, running roughly north-south.

The image shows the Indian plate which slides underneath the Myanmar plate at about 2 cm a year along the line marking the plate boundaries. Scientists think the Myanmar plate was pushed up about 10 to 20 metres when the earthquake struck, forcing the water above into the destructive waves.

Seismologists at North-western University in Illinois have upgraded the quake to magnitude 9.3, three times bigger than previously thought and the second largest ever recorded.

Little research has been done in the region and there are no maps of what the fault looked like before the earthquake, making it difficult for experts to pinpoint how it moved.

There are signs of recent activity. The image from the British survey ship shows two landslide blocks on the Indian plate, each about 2 km across and 100 metres thick. The earthquake probably shook them loose and slip scars can be seen. Dr. Russell Wynn, of the Southampton Oceanography Centre, England, said: ``An area the size of a small town fell away from the slope and broke up into bits.

Slabs of material

Slabs of material travelled about 10 km down the slope on to that flat bit of Indian plate and are just lying there. We don't know for definite that was caused by the recent earthquake but it's a very fresh looking feature.'' One of the researchers on board HMS Scott, Dr. David Tappin of the British Geographical Survey, said the images he had seen showed seabed movement, landslides and tectonic plate movement. ``There has been a lot of movement over a distance of about 1,000km and there is evidence that there has been several phases of movement,'' said Dr. Tapin

- Guardian Newspapers Limited 2004

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