In the wake of the 6.5-magnitude earthquake in China’s Yunnan Province on August 3 that claimed the lives of more than 600 people, Chinese geologist Fan Xiao has released new data that supports a link between that event and the region’s mega-dams.
Chinese geologist and environmentalist, and the author of several reports for Probe International, Fan Xiao is the former chief engineer of the Regional Geological Survey Team of the Sichuan Geology and Mineral Bureau.
The 6.5-magnitude earthquake that devastated southwestern China’s Yunnan Province on August 3 has reignited speculation that the pace of large dam construction in a geologically vulnerable region, criss-crossed by active faults, is behind a jump in seismic activity, including the early August quake in Yunnan’s Ludian County.
Chinese geologist Fan Xiao, who has been instrumental in sounding the alarm on unchecked dam development in the country’s seismically active southwest, released his research findings this month on the deeper relationship between seismic events in the Sichuan-Yunnan region – an area that has been struck by a rash of earthquakes in recent years – and impoundment of the massive Xiangjiaba and Xiluodu dam reservoirs on the Jinsha/upper Yangtze River (the Xiluodo reservoir is located 40 km away from the epicenter of the Ludian earthquake).
Spanning a four-and-a-half year period from January 1, 2012 to July 31, 2014, Fan discovered a dramatic surge in seismic activity in the two reservoir regions after late October 2012, an increase that also coincided with the rapid and substantial rise of water levels at both the Xiangjiaba and Xiluodu reservoirs. Not only did earthquakes of ≥ 2M increase significantly and become widespread in this region but four dense seismic clusters also appeared as a result.
“The Jinsha, on which the Xiluodu and Xiangjiaba dams are located on, actually flows through two northeast and northwest fault belts, with the end-to-end reservoirs basically parallel to or along these fault lines,” writes Fan. “Thus, the region’s complex and active geology means the reservoirs behind the dams are more likely to trigger an increase in RIS.”
According to Fan’s analysis, the areas worst affected by seismic activity include the one close to the rupture that led to the Ludian earthquake.
“Considering the geological context of the seismically risk-prone Sichuan-Yunnan region, stronger quakes are likely,” says Fan, “because reservoir water will flow along fracture belts and will penetrate deeper and deeper than previously in the initial phases of impoundment.”
Scientists have observed that the phenomenon of reservoir-induced seismicity (RIS) is related to the filling and draw down of reservoirs and the rate at which it happens. Pressure created by the weight of the reservoir water, and the infiltration of water into seismic faults and fissures, can trigger tremors, earthquakes and geological disasters such as landslides, mountain collapses, mud-rock-flows and so on. The significance and role of RIS is a topic that has sparked escalating debate ever since a devastating magnitude-8 earthquake struck China’s Sichuan Province in May 2008 (known as the Wenchuan earthquake, named after the location of the quake’s epicenter in Wenchuan County). The event unleashed a chorus of analysis that the Zipingpu reservoir may have contributed to the severity of the earthquake, or helped to trigger it.
The Ludian earthquake is “very similar” to the Wenchuan earthquake in that it has also triggered a series of secondary events of significant magnitude, says Fan – the landslides, mountain collapses, mudslides and so on, that result from seismic events.
Once again, Fan Xiao is calling for the urgent monitoring of large dams in areas prone to seismic hazard, for more attention to be paid to the risk of strong RIS-related events and the most vulnerable regions prepared for more frequent and stronger earthquakes.
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Patricia Adams, Executive Director, Probe International
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