Two earthquakes this year that struck China’s southwest Yunnan province, dotted with major Himalayan rivers and dams, are stirring up concerns that the seismic zone may be becoming more active.
This year’s Ludian earthquake, which killed 617 people and injured 2,400 in August, has shaken up both government and non-government seismologists, who are raising concerns about possible linkages between the region’s hydropower dams and seismic activity.
“After 18 years of inactivity, Yunnan, located in a seismic zone, has entered a new active phase. These three earthquakes may indicate that a bigger quake is going to occur," says Sun Shihong, a research fellow at the China Earthquake Networks Center.
According to Chinese seismologist Fan Xiao, whose latest findings were reported this fall in the scientific journal Nature, earthquakes of at least 2-magnitude grew more frequent from late 2012 through July 2014, around the time when the 6.5-magnitude Ludian earthquake occurred. The heightened activity strongly correlates with the filling of reservoirs in the Jinsha River area.
Fan’s research depicts three seismic clusters in which major earthquakes have been highly concentrated: one near a dam site at Xiluodu, another at the tail of the Xiangjiaba reservoir, and a third near the tail of the Xiluodu reservoir, which is close to the fault whose rupture led to the Ludian earthquake.
Reservoirs Filled Rapidly
Located on the main stem of the lower Jinsha, with a height of 285.5 meters and a storage capacity of 11.57 billion cubic meters, the Xiluodu Dam is China’s second-largest hydropower station, after the Three Gorges Dam. Back in 2005, the former State Environmental Protection Agency (SEPA) suspended construction of the Xiluodu Dam for “violating regulations.”
This past July, water levels in the Xiangjiaba reservoir rose a total of 100 meters, increasing its total storage capacity by 4.9 billion cubic meters in just 11 months. Similarly, Xiluodu’s levels increased by 132 meters and its total storage capacity increased by more than 7 billion cubic meters in 15 months.
“It is noteworthy that the water levels of the two reservoirs were not being increased gradually during these periods, but were raised rapidly in several short periods of impoundment during the 11 months and 15 months respectively,” Fan Xiao told the Chinese magazine Caixin. “In both cases, the rise in water levels in these two reservoirs breaks previous records at other big dams in China and abroad. Doing so was very dangerous.”
Arguing on similar lines is Yang Yong, an independent geologist and director of the Hengduan Mountain Research Institute in Chengdu city, who points out that the epicenter is just seven kilometers from Tianhuaban dam in the Niulan cascade and 10 kilometers from the Xiluodu dam on the Jinsha river, a tributary of the Yangtze.