An earthquake that killed at least 80,000 people in Sichuan last year may have been triggered by an enormous dam just miles from the epicentre.
The 511ft-high Zipingpu dam holds 315 million tonnes of water and lies just 550 yards from the fault line, and three miles from the epicentre, of the Sichuan earthquake.
Now scientists in China and the United States believe the weight of water, and the effect of it penetrating into the rock, could have affected the pressure on the fault line underneath, possibly unleashing a chain of ruptures that led to the quake.
Fan Xiao, the chief engineer of 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,” said Mr Fan. “This earthquake was very unusual for this area.
There have been no seismic activities greater than a magnitude seven quake along this particular seismic belt before.”
The 7.9 magnitude quake struck last May and left more than five million people homeless. It remains a raw and emotional topic for most Chinese, and the government has been quick to quash any suggestion that Zipingpu may have been responsible for the catastrophe. Researchers have been denied access to seismological and geological data to examine the earthquake further.
Zipingpu is only one of nearly 400 hydroelectric dams in the earthquake zone. Mr Fan said the government had been warned of the danger of 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 ten 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,” he said.
Although Sichuan is an earthquake-prone region, many scientists were caught by surprise by the magnitude of the quake. Christian Klose, a scientist at 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 argued that the sudden shift of a huge quantity of water into the region could have simultaneously relaxed the tension between the two sides of the fault, allowing them to move apart, and also increased the direct pressure enough to cause a violent rupture. The effect was “25 times more” than a year’s worth of natural stress from tectonic movement, he said.
Although the official government line is that its massive construction projects had nothing to do with the quake, some state researchers in Beijing have called for a full investigation. Lei Xinglin, of the China Earthquake Administration, said that the Zipingpu reservoir “clearly affected the local seismicity and it is worthwhile to study the role it played in triggering the earthquake further”. He added that firm conclusions remain “premature” however.
There is a history of earthquakes triggered by dams, including several caused by the construction of the Hoover dam in the US, but none of such a magnitude.