Big Bad Wave

December 28, 2004

Tidal Wave Began Beneath Indian Ocean
By THE ASSOCIATED PRESS

LONDON (AP) -- The chain reaction that sent enormous, deadly tidal waves crashing into the coasts of Asia and Africa on Sunday started more than six miles beneath the ocean floor off the tip of the Indonesian island of Sumatra.

Geologic plates pressing against each other slipped violently, creating a bulge on the sea bottom that could be as high as 10 yards and hundreds of miles long, one scientist said.

``It's just like moving an enormous paddle at the bottom of the sea,'' said David Booth, a seismologist at the British Geological Survey. ``A big column of water has moved, we're talking about billions of tons. This is an enormous disturbance.''

Moving at about 500 mph, the waves took more than two hours to reach Sri Lanka, where the human toll has been horrific, and longer to spread to India and the east coast of Africa.

...

The underwater quake, which the U.S. Geological Survey put at magnitude 9.0, was the biggest since 1964, when a 9.2-magnitude temblor struck Alaska, also touching off tsunami waves. There were at least a half-dozen powerful aftershocks, one of magnitude 7.3.

Enzo Boschi, the head of Italy's National Geophysics Institute, likened the quake's power to detonating a million atomic bombs the size of those dropped on Japan during World War II, and said the shaking was so powerful it even disturbed the Earth's rotation.

``All the planet is vibrating'' from the quake, he told Italian state radio. Other scientists said it was early too say whether the rotation was affected by the quake. ...

... The force of Sunday's earthquake shook unusually far afield, causing buildings to sway hundreds of miles from the epicenter, from Singapore to the city of Chiang Mai in northern Thailand, and in Bangladesh.

The quake probably occurred about 6.2 miles beneath the ocean floor, causing the huge, step-like protrusion on the sea bed and the resulting tidal waves.

As the waves moved across deep areas of the ocean in the early morning, they may have been almost undetectable on the surface, with swells of about a yard or less. But when they approached land the huge volumes of water were forced to the surface and the waves grew higher, swamping coastal communities and causing massive casualties.