When it struck, we worried that May's massive Wenchuan earthquake in Sichuan province could catastrophically imperil nearby dams. Now a growing number of scientists are suggesting that the quake was triggered by the weight of a reservoir created by a dam less than four miles from a major fault.
A report by a Columbia University researcher (pdf) presented to the American Geophysical Union in December coincides with a recent finding by Chinese geophysicists that the dam caused significant seismic changes before the earthquake.
Given that dams are known to cause tremors, we mentioned the possibility that the world-beating Three Gorges Dam might have triggered the Wenchuan quake. But the idea was written off as preposterous at the time by officials and government-funded researchers.
Despite the new reports, many scientists inside and outside China remain suspicious of the link, calling preposterous the notion that such an enormous quake could have been triggered by a five-year-old dam.
The research is politically controversial too, potentially adding to weight to criticisms of China's dam building efforts. The construction of the Three Gorges Dam led to the largest relocation of people in history, an initiative that the government has acknowledged has been plagued by social problems, as well as landslides, pollution and tremors in the region. Yesterday, China announced it would again be moving an unknown number of relocated farmers to cope with these problems.
The new findings could also be explosive as China continues to sort through the wreckage of the quake, which killed 80,000 people. Nine months on, the government continues to suppress critical news coverage of the widespread collapses of schools. Officials have also silenced the parents of the victims, who have tried to sue the local government for neglect.
The final straw
It's unclear how exactly the Zipingpu reservoir may have triggered the quake, and even those who say it did underscore that its effect was more akin to the last straw than the underlying cause, and probably only affected the timing of the quake, not its magnitude.
The average time for quakes on this particular Sichuan fault line is a thousand years, making the seismic risk of building a nearby dam low. The reservoir was filled between 2005 and April 2008, but pressure on the fault would have been building up for years, insist scientists. (Some reports suggest that the level of the reservoir dropped slightly the week before the quake.)
"The weight of these reservoirs themselves is insufficient to cause an earthquake," geophysicist Rob van der Hilst of MIT told Wired Science. "It could be that the stress field is perturbed by the reservoir, but how exactly it translates into the onset of an earthquake, we just don't know."
(Wired also has a post explaining how to cause a man-made earthquake.)
Studying the data
Key will be the sharing of seismological data from the area with scientists around the world. While that data has yet to be made widely available, it is likely China's researchers will continue to study it in the hopes of preventing future disasters.
Even as the link between the dam and the quake remains sketchy, the new research is certain to trigger new concerns about the safety of massive dam building projects in China and elsewhere. These are concerns that the Chinese government, no matter how well it manages to muffle them, will not be able to ignore.
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