Chinese earthquake,a result of the geological processes that created the Himalayas
source: http://www.theaustralian.news.com.au/story/0,25197,23693851-30417,00.html
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Mount Everest and the Himalayas form part of the Tibetan Plateau and are still rising because of the collision, 45million years ago, between the Indian and Eurasian tectonic plates.The epicentre of Monday's earthquake lies on a fault line between the eastern border of the Tibetan Plateau and an area of sedimentary rocks.Material from the plateau is forcing its way underneath the Sichuan basin sedimentary rocks lying deep beneath the surface in China. Friction between the rocks holds up the movement, and an earthquake occurs when the opposing surface suddenly slips forward as the massive forces overcome the friction.John Whalley, a geologist at the University of Portsmouth in southern England, compared the process to attempting to push a heavy piece of furniture across the floor."It's like trying to move a wardrobe on a carpet - you have to build up your push, then you get a jog of movement," Dr Whalley said.The Himalayan mountains and the Tibetan Plateau are still being forced northwards and upwards by the Indian plate, moving at a rate of 5cm a year.Seismologists say the earthquake's epicentre was beneath Wenchun county, about 160km northwest of the city of Chengdu. It is calculated to have taken place 10km below the surface, a relatively shallow depth that is thought to have contributed to the violence of the earthquake on the ground.Energy from the subterranean slip spread out in every direction, and the powerful earthquake, which was measured at magnitude 7.8, could be felt as far away as Bangkok and Hong Kong, and in Shanghai, 1500km away.Dr Whalley said of the collision between the Indian and Eurasian tectonic plates: "The Himalayas and the Tibetan Plateau are the consequences of this continuing northwards push. As well as creating these extensive high areas, India's push generates an eastwards spread of material away from the Tibetan Plateau."In the Sichuan area, the margins of the plateau are being pushed under weaker sedimentary rocks. It is along one of the faults marking the boundary of these sediments that the earthquake occurred."
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