Dams and Earthquakes

Chinese scientists talk about the Zipingpu reservoir-triggered earthquake

(December 15, 2008) In the wake of the big earthquake which occurred in China’s Sichuan province on May 12, 2008, there has been much discussion about ecological disasters caused by hydro dam construction, including the possibility that dams could induce earthquakes in China and elsewhere. To better understand the issue, Science Times interviewed two members of the CAS (Chinese Academy of Sciences) recently: Pan Jiazheng, [1] a preeminent expert in hydro engineering, and Chen Houqun, a leading expert in earthquake safety engineering in China.

According to official statistics, as many as 2,830 reservoirs nationwide were damaged by the May 12 earthquake, with 69 dams in danger of collapse in Sichuan province alone. Professor Pan Jiazheng points out that not all the 2,830 reservoirs were located in the earthquake-affected area, and that most of them were small reservoirs. Only four or five medium or large hydro dams were in the most affected region, namely in the Min valley upstream of the city of Dujiangyan. Zipingpu and Shapai, two high dams which were closest to the epicenter of the May 12 earthquake, were not seriously damaged and were easily repaired.

“More importantly, the loss resulting from the damage to the dams was limited to the dam itself and downstream areas escaped serious harm.[2] On the contrary, those hydro dams played an important role in the work of protecting property and rescuing people. For example, some projects were still operating after the big earthquake, providing electricity, and the reservoirs were used as waterways to transport materials to the earthquake-affected area,” Professor Pan said. “The media has been incessantly questioning the wisdom of building more and more hydro dams in earthquake-prone southwest China, but ignoring the fact that these water projects have played a significant role in the economic development of the region by supplying water for human use and for irrigation and so forth, which is not fair,” he added.

As for the controversy over whether building large hydropower projects induces earthquakes or not, Professor Pan said, “It’s impossible for the reservoirs to ‘make’ earthquakes, but what the reservoirs can do is to influence weak links to enable seismic activity to occur earlier. Therefore the earthquake research community tends to use the word ‘reservoir triggered-earthquake’.” While it is true that reservoir triggered-earthquakes are not uncommon, Professor Pan made it clear that “the earthquake research community outside and inside China has widely accepted the notion that the May 12 Wenchuan earthquake was a huge natural disaster caused by massive crustal movement, because no reservoir triggered-earthquake with a magnitude eight has ever occurred in history. And if the Zipingpu dam reservoir did play a role in the big earthquake, it was actually to reduce the energy released by the earthquake in general.”

Professor Pan told the Science Times reporter that, as a result of the extra large earthquake that occurred in Sichuan, he is even more confident about building more high dams and big reservoirs in southwest China. And he disagrees with the call “To temporarily suspend building large dams in geologically unstable zones in southwest” put forward by some Chinese experts. Instead, he argues, China must continue to build more hydro projects in the region to regulate and exploit water resources, especially as suspending dam construction would not solve geological disasters such as seismic activity, but rather make the situation worse.

Professor Pan emphasizes, however, that he favors strengthening safety standards in water project construction. “To learn lessons from the big Wenchuan Earthquake, it’s necessary to assess hydro projects that are under construction in southwest China, especially their ability to withstand seismic forces. The work should concentrate on several key dam projects, focusing on the maximum magnitude earthquake that dams in the region can withstand and using this analysis for the design of future dams.” Pan Jiazheng said he firmly believes that further in-depth study and analysis would prove the benefits of large dams and that larger hydro projects, able to withstand earthquakes of greater magnitudes, should be built for generations to come.

Referring to the Zipingpu dam which was damaged by the May 12 earthquake, Professor Chen Houqun, another leading scientist in earthquake safety engineering in China, said, “generally speaking, the main structure of the Zipingpu dam is stable after the earthquake, though deformation, cracks and other problems were found in the dam structure. But because it withstood an earthquake with a larger seismic intensity than it was originally designed for, this indicates that the dam was carefully designed and built.”

Regarding the possibility that the Zipingpu dam induced the earthquake, Professor Chen responded confidently that “the Zipingpu had nothing to do with the Wenchuan earthquake at all,” adding that “not all high dams and big reservoirs are able to trigger earthquakes.”

“First, filling the Zipingpu reservoir had no impact on the hydrogeological conditions (of the Beichuan-Yingxiu Fault Belt),” because the reservoir is located between the Beichuan-Yingxiu Fault Belt and Jiangyou-Guanxian Fault Belt, and because Zipingpu was operating at a normal pool level of 875 meters, which was lower than the natural water level of 877 meters in the Min River.

“Second, the seismic activity both before and after the filling the Zipingpu reservoir was unchanged,” he added. “Based on the monitoring data available from October 2005, when the reservoir started filling to April 2008, before the earthquake occurred, the location, frequency and intensity of seismic activity was within the normal range. There were small changes during that period of time, but these changes would have occurred even if the dam had not been built.”

[1] And one of chief designers and head of the inspection team for the Three Gorges dam.

[2]  In the event that the dams had collapsed – as was feared — and a tsunami had rolled down the valley wiping out everything in its path.

Xia Shuang, Science Times (Kexue shibao), December 15, 2008

Translated by Three Gorges Probe

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