Mapping movements: This Dec 28, 2004, image from the US National Oceanic and Atmospheric Administration shows the epicentre of the quake marked with a red star, located east of the Sunda Trench, where the India Plate begins to get subducted beneath (forced under) the Burma Plate. The blue arrows along the plate boundary show the direction of subduction. As the India Plate slides beneath the Burma Plate, it meets pockets of resistance, which causes compressional forces to build up. When the bottom of the ocean is deformed by this type of ‘megathrust’ quake, the upward force acts like a fist rising up from underwater (see graphic on page 19). Water rolls down off the sides of the ‘fist’, creating massive waves that can travel as fast as an airplane. The waves can move across the ocean and barely disturb the surface, but when they reach shallow coastal water, the earthquake’s energy thrusts them tens of meters into the air. – AFP/NOAA
Geologists are striving to provide sound science so policy makers and people in vulnerable areas can make the right decisions.
A GEOLOGICAL time bomb is ticking in Indonesia, and the city of Padang on Sumatra’s western coast is sitting smack on top of it.
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