Sichuan quake highlights threat to China's dams

The magnitude 6.6 earthquake that shook China's Sichuan province on 20 April, killing over 180 people, was small compared to the magnitude 7.9 quake that struck the region in May 2008, claiming some 69,000 lives. But it provided a sobering reminder that many of China's engineering projects are vulnerable because they sit along fault lines ? and raises questions about whether they could, in part, be to blame.

In unstable regions like Sichuan, it is critical to look at how building reservoirs, for example, might affect the local seismology, says Shemin Ge of the University of Colorado in Boulder. Ge and her colleagues have suggested that the 2008 quake may have been partially triggered by the creation a few years earlier of the giant Zipingpu Reservoir 20 kilometres from what would be the epicentre. The reservoir would have ratcheted up the pressure on the rocks beneath.

It's too early to know whether reservoir-building contributed to last week's quake. Of more immediate concern is the damage to dams and reservoirs, says Mian Liu of the University of Missouri in Columbia. According to the Ministry of Water Resources, two medium-sized and 52 small dams were damaged, with residents evacuated downstream of five of them.

Determining the factors behind the recent quake could help inform where future projects are sited, says Ge. China has already planned to build 60 hydropower dams between 2011 and 2015, many of which will lie along fault lines as these form natural sites for river courses. In theory, dams can be designed to withstand any amount of shaking.

The 2008 quake, whose epicentre was 85 kilometres away, may also have contributed to the latest event, by redistributing pressure along the Longmen Shan fault line, says Liu. In the aftermath, he calculated that it had increased the risk of another magnitude-7 quake within the next 50 years by a few per cent. "Seems nature was in a hurry," he says of last week's quake.

Although it's impossible to predict any quake with certainty, the area now most at risk, Liu says, is the Aninghe fault line further south ? the two recent quakes may have slightly increased the stresses there.

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