Dam could have triggered Chinese earthquake, say scientists

Weight of water may have affected disaster that killed 90,000 in Sichuan last year

• Tania Branigan, Beijing
• guardian.co.uk, Thursday 5 February 2009 12.49 GMT

Pressure from a large dam could have helped to trigger the earthquake which killed up to 90,000 people in south-west China last year, some scientists have claimed.

Chinese and overseas experts suggested that the weight of waters in the Zipingpu Dam in Sichuan may have affected the timing or scale of the 7.9 magnitude quake. The dam stands just 3.5 miles from the epicentre.

Scientists agree that dams can produce tremors. But several today played down the claims that this was an issue in Sichuan, arguing that the area lies on an active fault line and that the shock was too great for the reservoir to be a major factor.

Fan Xiao, a chief engineer at the Sichuan Geology and Mineral Bureau, said May's earthquake was the largest in the area for thousands of years and suggested that the weight of the reservoir's waters – 315m tonnes – was a key factor.

"I'm not saying the earthquake would not have happened without the dam, but the presence of the massive Zipingpu dam may have changed the size or time of the quake, thus creating a more violent quake," he told the Associated Press in a telephone interview.

Fan said sudden changes in the water level – like the rapid drop at Zipingpu shortly before the quake – could greatly destabilise an existing fault.

He added that he had opposed the dam's construction in 2003 because he was worried about such a disaster and was concerned that dams are now being built on the Dadu and Jinsha rivers to the west and north-west of the quake zone.

The Chinese government has promoted the building of large dams to reduce flooding and meet the country's energy needs without increasing pollution from coal-fired power stations.

Christian Klose, a geophysical hazards research scientist from Columbia University in New York, has also suggested the extra water could have triggered the earthquake.

But in a blog posting on the subject he warned: "Scientific evidence for such a statement is needed! Some questions need to be answered: How much water was impounded, where and when? Did resulting stress changes alter stresses deep in the Earth's crust? Were stress alterations significantly large enough? Where was the highest seismic energy release – close to the reservoir?"

Dr Alex Densmore of Durham University, who was studying the Sichuan fault before the quake and has carried out further work there since, said he was "pretty sceptical".

"The fault the earthquake happened on is active; we know there have been earthquakes there in the past and geologically that happened yesterday – just a few thousand years ago. It's impossible to say whether or not the reservoir might have advanced the time of the earthquake, but if it did so it did it by a very short period.

"The size of the earthquake is ultimately determined by the length of the fault which breaks and how far the two sides move relative to each other. A reservoir by itself isn't going to affect those things … It won't give you a bigger earthquake than you would otherwise have had."

Dr Roger Musson of the British Geological Survey said the Aswan Dam was a good example of how large reservoirs could produce earthquakes in previously unaffected areas.

But he said he would be extremely doubtful that the Sichuan dam had played a role unless there was a record of smaller quakes dating back to when it was filled.

Musson added: "That kind of [induced] earthquake can go up to magnitude 6.5, let's say. This earthquake was totally outside that level and was on a 300km-long rupture. That's a major tectonic fault.

"To my mind it's a sterile discussion [anyway] – either the earthquake is going to happen or it's not. If you have advanced it by a year or two, is that a big deal?"

Lei Xinglin, a geophysicist at the government's China Earthquake Administration, called for further investigation.

"A reservoir in the region will have positive and negative effects on a potential earthquake, but it is ridiculous to say an earthquake was caused by the dam," he told AP.

"We still need to carefully research this topic rather than jumping to conclusions."