Tibetan tectonics triggered China quake
The violent quake that shook China's Sichuan province this week is linked to a shift of the Tibetan plateau to the north and east, researchers say.
"There will certainly be many aftershocks," says Paul Tapponnier from the Paris Institute of Earth Physics, an expert on tectonics in the region.
The quake, with a magnitude of 7.8, struck close to densely populated areas of Sichuan province and was felt across southeast Asia.
Buildings swayed in Beijing and Shanghai, while the quake was felt in Hong Kong, Vietnam and in the Thai capital Bangkok, 1800 kilometres from the epicentre.
China's state-run Xinhua news agency quoted local disaster relief officials as saying 3000-5000 people were estimated to have died in just one district of Sichuan, Beichuan County.
Earthquakes are frequent and deadly along the fringes of the Tibetan plateau, which was raised when India collided into Eurasia, starting some 50 million years ago.
It is this powerful thrust that created the Himalayas, with Mount Everest the highest peak.
The mountains continue to reach skyward to this day, propelled by unstable tectonic terrain.
"Tibet is being pushed to the east. It is straddling southern China and locally the Sichuan basin," says Tapponier.
The quake that emanated in the Longmenshan margins of the Tibetan plateau "has a very complex geology", says the institute's Robin Lacassin.
"There are many major fault lines ... Some are ancient and they probably broke," says Lacassin.
The quake's epicentre was about 93 kilometres from Chengdu, a city of more than 12 million people, and 260 kilometres from Chongqing and its 30 million.
It struck from a depth of just 10 kilometres, according to the US Geological Survey.
An official says the landmark Three Gorges Dam in Sichuan province has not been affected.
An Olympic spokesperson says none of the 31 venues for the Beijing Olympics in the capital and other host cities have been damaged.
The deadliest earthquake to rock the Tibetan plateau in the 20th century was in 1920 when 230,000 people died in Gansu province.
Another quake in Yunnan in the southwest left more than 15,000 dead in 1970.