(March 22, 2013) A new Probe International exclusive report by Chinese geologist Fan Xiao calls for urgent monitoring of China’s large dams in areas prone to seismic hazard. These areas may be at increased risk from dam reservoir-induced seismicity (RIS). Scientists have observed that reservoir impoundment may not only increase the risk of strong earthquakes, particularly in areas already vulnerable to high-intensity seismic activity, but may represent a more pronounced risk in the first few years after a dam is filled.
By Lisa Peryman for Probe International
A new report exploring the risk of reservoir-induced seismicity (RIS) in China’s southwestern Sichuan-Yunnan region, an area that has been struck by a rash of earthquakes in the past year, suggests there is cause for heightened concern in this region regarding the probability of reservoir-induced seismicity, and especially the risk of strong RIS.
Authored by Chinese geologist Fan Xiao*, the report states that while there is no evidence, yet, that the recent string of moderate to strong earthquakes that have occurred in the Sichuan-Yunnan region were induced by dam reservoirs, the frequency of seismic activity in the area exposes a geological vulnerability that unchecked construction of giant, even super-sized hydropower projects will provoke.
Fan Xiao warns that the government’s current plan to build huge, cascading dams, close together, along the great rivers of Sichuan-Yunnan in actively seismic zones increases the probability that these dams will both induce and be damaged by seismic activity. He adds that the next 10 years represent an especially dangerous period as scientists have observed that reservoir-induced seismicity is most likely to occur within the first few years after a dam is filled. Typically, it takes time for reservoir water to penetrate deep into seismic faults and fissures before it triggers seismic activity.
For his report, Fan Xiao compiled a list of earthquakes with magnitudes greater than 4 and looked in particular at two dams in the region. He found that some 1,834 small earthquakes recorded in the Pubugou Dam reservoir area, from October 2006 to December 2011, should not be dismissed as unrelated to the impoundment of Pubugou’s reservoir. Although experts at the Sichuan Seismological Bureau had ruled out a connection between the quakes and RIS, Fan Xiao said it was too early to tell.
Meanwhile, the Xiangjiaba Dam represents an unprecedented example of extremely rapid reservoir filling. Fan Xiao notes scientists have observed that RIS is related to the filling and draw down of reservoirs and the rate at which it happens. He writes:
“Therefore, this practice at Xiangjiaba undoubtedly increases the risk of reservoir induced seismicity and other reservoir induced geological disasters (such as landslides and mountain collapses).”
This year, from September to December, the Xiangjiaba reservoir will rise another 26 metres to its normal pool level of 380 metres above sea level, reports Fan, which, as with Pubugou, propels the Xiangjiaba reservoir area into a particularly dangerous period. The probability of RIS in the next few years is not only heightened, says Fan Xiao, it could even last for a decade or more.
“The situation must be closely monitored.”
Read the full report here.
* Fan Xiao is a Chinese geologist and chief engineer of the Regional Geological Survey Team of the Sichuan Geology and Mineral Bureau.
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