Was the 2008 Sichuan earthquake provoked by dam construction?

2008 Sichuan earthquake. Illustration: Wikimedia Commons

The construction of a dam near the earthquake’s epicenter may have hastened an impending earthquake by up to several hundred years, according to a recently published study by U.S. researchers.

The May 12, 2008 Sichuan earthquake in south central China measured 8.0 Ms and 7.9 Mw on the Richter Scale. It resulted in the deaths of at least 68,000 people and many thousands more are still officially listed as missing. Its impact was felt in several neighboring countries and made buildings sway in places as far away as Shanghai, located 1,056 miles (1700 kilometers) from the epicenter.

An American research team headed by Shemin Ge of the department of Geological Sciences at University of Colorado in Boulder, has raised the possibility of the dam being involved. The team’s conclusions are outlined in a paper recently published in Geophysical Research Letters.

This is the first time that a major international revue has published theoretical research on the possibility of the dam being implicated. The study’s conclusions are contained in the abstract, which reads:

“The devastating May 2008 Wenchuan earthquake (Mw 7.9) resulted from thrust of the Tibet Plateau on the Longmen Shan fault zone, a consequence of the Indo-Asian continental collision. Many have speculated on the role played by the Zipingpu Reservoir, impounded in 2005 near the epicenter, in triggering the earthquake. This study evaluates the stress changes in response to the impoundment of the Zipingpu Reservoir and assesses their impact on the Wenchuan earthquake. We show that the impoundment could have changed the Coulomb stress by −0.01 to 0.05 MPa at locations and depth consistent with reported hypocenter positions. This level of stress change has been shown to be significant in triggering earthquakes on critically stressed faults. Because the loading rate on the Longmen Shan fault is <0.005 MPa/yr, we thus suggest that the Zipingpu Reservoir potentially hastened the occurrence of the Wenchuan earthquake by tens to hundreds of years.”

Their research also contains the precise timescale of the filling operations at the Zipingpu dam. They state that the dam was filled in fall 2005 in a very rapid manner and that, contrary to official declarations at the time, the dam was not emptied thereafter. This evidence is said to indicate that water infiltration into the nearby fault, along with its associated lubricating properties, could have had an impact on the fault’s behavior.

Rumors concerning the possible implication of the construction and reservoir-filling of a recently constructed dam in the earthquake zone began circulating soon after the event. The Zipingpu dam was commissioned in 2004 and is 511 feet high, with a capacity of 315 million tons of water. It is estimated to be 550 yards from the fault line which ruptured in the earthquake -- the Longmen Shan fault -- and about three miles from the earthquake’s epicenter.

Fan Xiao, the chief engineer of the Sichuan Geology and Mineral Bureau in Chengdu, told the Daily Telegraph in February of this year that it was "very likely" that the construction and filling of the reservoir in 2004 had led to the disaster. The Chinese Science Academy dismissed the claims, saying that the earthquake had been provoked by natural forces.

Other official statements concerning the dam said that it was being emptied at the time of the earthquake, leading some specialists to consider the possibility that the ensuing modification of pressure being brought to bear on the fault line by the reduced weight of water could have played a role in the disaster which followed.

The increase of microseismicity due to the building and filling of dams is a phenomenon that has been acknowledged since the 1940s. It was first studied in the United States after the construction of the Hoover dam on the Colorado River. Seismologists have established that at least twelve earthquakes of magnitudes between 3 and 6 have been provoked by hydraulic installations.

The most serious of those incidents known today was the 1967 Koyna dam disaster in India which provoked an earthquake of 3.6 and resulted in the deaths of over 200 people. The dam itself was destroyed.

The University of Colorado team says it will continue to research the characteristics of microseismicity, as well as related research into the frequency of major earthquakes in the area and their causes, in order to help determine more precisely if the dam could have had an effect on the timing of the 2008 earthquake.