Malcolm Moore in Shanghai
February 4, 2009
THE earthquake that killed at least 70,000 people in China last year could have been caused by the presence of an enormous dam near the epicentre, scientists said.
The 150-metre-high Zipingpu Dam holds back 315 million tonnes of water. It lies 500 metres from the fault line and five kilometres from the epicentre of the earthquake in Sichuan province.
Scientists in China and the United States believe that the weight of water, and the effect of it penetrating into the rock, added to the pressure on the fault line, possibly unleashing a chain of ruptures that led to the quake.
Fan Xiao, a chief engineer at the Sichuan Geology and Mineral Bureau in Chengdu, said it was "very likely" that the construction and filling of the reservoir in 2004 had led to the disaster. "There have been many cases in which a water reservoir has triggered an earthquake. This earthquake was very unusual for this area," he said.
The quake, measuring 7.9 on the Richter scale, struck on May 12 and left more than 5 million people homeless. It remains a raw and emotional topic in China, and the Government has been quick to quash any suggestion that the dam was to blame.
Researchers have been denied access to seismological and geological data to examine the cause of the quake further. Zipingpu is one of nearly 400 hydro-electric dams in the earthquake zone.
Mr Fan said the Government had been warned about building so many large-scale projects in a seismically active area, but that the warnings had gone unheeded. "I not only opposed the construction of Zipingpu but also the overdevelopment of the reservoirs on Minjiang River. There are 10 major reservoirs on the main river, 29 on its tributaries and a lot more smaller-scale reservoirs, all of which block the flow of the entire river, and are very hazardous to the local geology."
Sichuan is an earthquake-prone region, but the magnitude of the quake took many scientists by surprise. Christian Klose, from Columbia University's Lamont-Doherty Earth Observatory, said there had not been any major seismic activity on that fault line for millions of years.
He said the sudden shift of a huge quantity of water into the region could have relaxed the tension between the two sides of the fault, allowing them to move apart, and could have increased the direct pressure on it, causing a violent rupture. The effect was "25 times more" than a year's worth of natural stress from tectonic movement, he said.
The government line is that its massive construction projects had nothing to do with the quake, but some state researchers in Beijing have called for an investigation.
Earthquakes after the construction of the Hoover dam in the US did not reach such a magnitude.
This story was found at: http://www.smh.com.au/articles/2009/02/03/1233423223292.html