(April 4, 2012) A new report finds more than 130 large dams being built in western China could trigger disaster — earthquakes, even tsunamis — due to their construction in seismic hazard zones.
More than 130 large dams that China is building in its western region, an area of high seismicity, are vulnerable to earthquakes or could induce earthquakes, according to a new report released by the Canadian-based environmental group Probe International. In a worst-case scenario, dams could collapse creating a tsunami that would wipe out everything in its path, including downstream dams, and cause untold loss of life and property.
To pierce the Chinese government’s secrecy over its dam-building, the Probe report overlays a Chinese map of dam locations with US Geological Survey earthquake data and a United Nations’ seismic hazard map. Probe also used Google Earth satellite images to confirm the state of completion of about one-half of the dams.
According to the report, 98.6% of the dams being constructed in western China are located in moderate to very high seismic hazard zones. The Zipingpu Dam, for example, which is now thought to have triggered the magnitude 7.9 Sichuan earthquake in 2008 that killed an estimated 80,000 people, was built in a moderate seismic zone. The force of that quake cracked the dam and shook it so severely that it sank one metre and moved 60 centimetres downstream.
The location of large dams near clusters of recorded earthquakes with magnitudes greater than 4.9, and especially when the earthquake focal points are also close to the surface, “is cause for grave concern,” said John Jackson, a geologist and the report’s author.
Earthquakes over M4.9 have been known to damage dams and other structures. Shallow earthquakes (less than 10 km deep) indicate active faults that could be reactivated by routine practices, such as the filling of a reservoir to accommodate flood waters and its drawdown to generate power, he says.
“In addition to the hazard of high natural seismicity in western China, reservoir-induced seismicity is likely to increase the frequency and perhaps the magnitude of earthquakes in this area,” he warns.
Western China is known to be a large regional stress field because of the rapid — geologically speaking — northward motion of the Indian subcontinent into western China. This “continental collision” has, for example, lifted seafloor sediments to the top of Mt. Everest and created the Tibetan Plateau. Since detailed recordkeeping began in 1973, nine earthquakes with a magnitude of 4.9 or greater have occurred in western China each year, on average.
Especially worrying in this environment, said Mr. Jackson, is the cascade-like positioning of the dams which follow one another so closely there is no terrain between them for energy to dissipate in the event of catastrophic dam failure.
“If one dam fails, the full force of its ensuing tsunami will be transmitted to the next dam downstream, and so on, potentially creating a deadly domino effect of collapsing dams,” he says.
China is the world’s largest hydropower producer with some 87,000 dams and reservoirs (about one-third are hydrodams), of which nearly half are considered to be dangerous and at risk of collapse.
In the interest of public safety and a sound power sector, the Probe International report urges the Chinese government to disclose the details of its current slate of dam construction, and to ensure that a thorough and independent regional seismic risk assessment is done without delay and publicly disclosed.
Chinese citizens are becoming increasingly vociferous in their outrage over lives risked, and lost, to shoddy standards, most recently in the country’s food and high-speed rail industry. Should a dam suffer catastrophic dam collapse, says Patricia Adams, Executive Director of Probe International, that anger would spill over to the hydropower industry for threatening ordinary citizens’ lives with dangerous dams.
To read the full report, see here
To read the full report in Chinese, see here
John Jackson is a pseudonym for a geologist with detailed knowledge of western China who must remain anonymous.