This blog offers updates, independent analysis and comments on international financial relations, the environment, and dams. As International Rivers' Policy Director and before, the coordinator of a Swiss NGO, I have advocated for human rights and the environment for more than 20 years. When I'm not at work, I spend time with my family, hike, and visit the opera. My favorite river is the Albula in the Swiss Alps.
Sichuan earthquake of May 2008 (mike at bloggin-ads.com)
Last year's devastating Sichuan earthquake, which took at least 69,000 lives, may have been unleashed by the huge Zipingpu Dam. New scientific evidence links the impoundment of the Zipingpu reservoir to the activation of a fault line near the dam site. A thorough scientific assessment is needed before China builds more dams in earthquake-prone areas.
It is well established that large dams can trigger earthquakes through what is called reservoir–induced seismicity. There is evidence linking earth tremors and the raising and lowering of reservoirs for more than 70 dams. Reservoirs can both increase the frequency of earthquakes in areas of already high seismic activity and cause earthquakes to happen in areas previously thought to be seismically inactive.
Zipingpu is a 156-meter-high dam on the Min River, a tributary of the Yangtze. The project, which displaced 33,000 people, was completed with Japanese funding in 2006. Fan Xiao, a chief engineer with the Sichuan Geology and Mineral Bureau, had warned about Zipingpu's seismic risks since before the dam was completed. After the disaster, he explained that “Zipingpu has all conditions that provoke reservoir-induced earthquakes,” and said that “we cannot rule out the possibility that building the Zipingpu Dam induced the earthquake because the epicenter is so close to the dam.” (Fan’s interview with the South Urban Daily, like other useful documents on the topic, has been translated by Three Gorges Probe.)
Zipingpu Dam (AP Photo/GeoEye Satellite Image)
Geophysical hazards researcher Christian Klose of Columbia University’s Lamont-Doherty Earth Observatory has found that the fault line that triggered the Sichuan quake had not been active for millions of years. Klose presented his research at a meeting of the American Geophysical Union in San Francisco in December. According to Klose, “the ensemble of geophysical observations suggests that the root cause of triggering the M7.9 Wenchuan earthquake may have stemmed from local and rapid mass changes on the surface.” As a news article on Klose's findings in the January 16 issue of Science elaborates, “the added weight [of the Zipingpu reservoir] both eased the squeeze on the fault, weakening it, and increased the stress tending to rupture the fault. The effect was 25 times that of a year’s worth of natural stress loading from tectonic motions. (…) When the fault did finally rupture, it moved just the way the reservoir loading had encouraged it to.”
In a recent paper in the Chinese journal Geology and Seismology, Lei Xinglin, a geophysicist at the China Earthquake Administration in Beijing, and four colleagues produced further evidence for the seismic impacts of the Zipingpu Dam. According to the paper, “some clear correlations were verified between the local seismicity and stress change, thus we concluded that the impoundment of Zipingpu clearly affected the local seismicity and it is worthwhile to further study if the effect played a role in triggering the Wenchuan earthquake.”
More research into the cause of the Wenchuan earthquake is needed. What is clear is that the tremor almost broke Zipingpu and other dams. During the quake, the fault line slipped up to seven meters upward. In a story in New Scientist, Fred Pearce describes that “as the tight valley sides juddered, the [Zipingpu Dam] structure was squeezed and ended up to 18 centimeters downstream, and 70 cm lower. The concrete was ripped apart but the core of the dam survived.” According to China’s Ministry of Water Resources, 69 dams were in danger of collapse after the earthquake in Sichuan Province alone, 310 were at “high risk,” and 1,424 posed a “moderate risk.”
At the time of the earthquake, the Zipingpu reservoir was half-empty. Pearce suspects that if the tremor had happened two months later during the monsoon season, “Zipingpu and the other dams would probably have failed,” inundating Dujiangyan, a city of 600,000, and other downstream areas. The reservoir is now empty, awaiting repair of the dam.
The mountainous areas of Sichuan and Yunnan Province are geologically unstable. Yet they are also at the center of current Chinese dam building. After the Wenchuan quake, 62 experts in geology, water management and environmental protection appealed to the Chinese authorities to “temporarily suspend the approval of big hydro dams in geologically unstable areas in southwest China.” They asked the government to take five measures, including studies to assess the risks of reservoir–induced seismicity in geologically unstable regions, and to assess the safety risks posed by cascades of dams to the downstream areas in earthquake-prone regions.
So far, the Chinese authorities have dismissed evidence linking the Zipingpu Dam to the Wenchuan quake, and have declined to release seismic data which would allow further research on this topic. At the same time, China is building dams like there is no tomorrow.
President Obama has promised to “restore science to its rightful place” in the United States. In China, the concept of scientific development has become the guiding principle of Hu Jintao’s presidency. Free scientific research and debate is now needed to assess the seismic risks of China’s massive dam-building program.
For more articles on the Zipingpu Dam and Sichuan Earthquake, see below:
If the Zipingpu, a dam on the Min River (a tributary of the Yangtze) which is merely 156 meters high can cause such a devastating earthquake, imagine what might be in store from the world's largest dam-- now under construction along the Yangtze. The Three Gorges Dam, approx. 185 meters high and 1.6 km wide, produces a reservoir nearly 600 km long. If the Chinese ignore the seismic risk and continue to build the Three Gorges dam, I fear we must be prepared for a much more deadly earthquake along this newly activated fault line.
A trigger is a device that sets in motion a sequence of actions that result in an explosive discharge. The explosive discharge is powered by chemicals, which in the presence of some catalyst (substance or applied energy) change into other chemicals, and cause the explosive discharge. For that reason, the hydrostatic pressure caused by the water impounded by the dam is aptly called a trigger. Unfortunately, many may assume the "trigger" produced the earthquake, when in fact, pent up stress in the earths crust was the energy source that the "trigger" actuated. Very similar to the powder in the bullet casing exploding causing the gun to fire when the trigger causes the hammer to fall on the detonator. In this region, the movement of tectonic plates continues to build up stress in the earths crust, the release of that stress at this point in time as a result of the hydrostatic pressure may have released stress that could have continued to build to even higher levels before it released and resulted in an even greater magnitude earthquake. In a way, "triggering" earthquakes that otherwise would not have occurred may serve to protect an area from even more devastating earthquakes in the future.
Some years ago scientists were contemplating using hydrostatic pressure along the San Andreas fault in California. The concept was to reduce the hydrostatic pressure at two points some distance apart along the fault line, "locking up" the fault and increase the hydrostatic pressure between the two points, "triggering" a small earthquake in that part of the fault as the hydrostatic pressure acted as a lubricant allowing the rocks on either side to move past each other more easily. Continue the process by leapfrogging along the fault triggering small earthquakes all along the fault. This process would relieve the strain building up as the northwest-bound North American plate moved past the southeast-bound Pacific plate in small segments at a time, avoiding the great earthquake an extensive rupture could cause. In view of the potential cost of failure in such an experiment, it seems to have been put on a back burner.
It's true many scientists prefer the term triggered, vs. induced, which may more realistically reflect most RIS/RTS cases worldwide (where reservoir loading sort of pushed the stress level past the breaking point, rather than providing the energy for the earthquake). Whichever term you use, it seems important to remember that no matter how direct of an impact human activities can have on seismicity, it's unquestionable that there will be unforeseeable costs regardless of whether we caused an earthquake, or just sped up a "natural one" (or in this case, according to Klose, produced an effect that was 25 times that of a year's worth of natural stress loading).
In terms of triggering earthquakes to prevent the next big one, here's what I found on the USGS site:
"Seismologists have observed that for every magnitude 6 earthquake there are about 10 of magnitude 5, 100 of magnitude 4, 1,000 of magnitude 3, and so forth as the events get smaller and smaller. This sounds like a lot of small earthquakes, but there are never enough small ones to eliminate the occasional large event. It would take 32 magnitude 5's, 1000 magnitude 4's, and 32,000 magnitude 3's to equal the energy of one magnitude 6 event. So, even though we always record many more small events than large ones, there are far too few to eliminate the need for the occasional large earthquake. As for "lubricating" faults with water or some other substance, if anything, this would have the opposite effect. Injecting high pressure fluids deep into the ground is known to be able to trigger earthquakes — to cause them to occur sooner than would have been the case without the injection. This would be a dangerous pursuit in any populated area, as one might trigger a damaging earthquake."
Comments
If the Zipingpu, a dam on
If the Zipingpu, a dam on the Min River (a tributary of the Yangtze) which is merely 156 meters high can cause such a devastating earthquake, imagine what might be in store from the world's largest dam-- now under construction along the Yangtze. The Three Gorges Dam, approx. 185 meters high and 1.6 km wide, produces a reservoir nearly 600 km long. If the Chinese ignore the seismic risk and continue to build the Three Gorges dam, I fear we must be prepared for a much more deadly earthquake along this newly activated fault line.
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Earthquake Triggers
A trigger is a device that sets in motion a sequence of actions that result in an explosive discharge. The explosive discharge is powered by chemicals, which in the presence of some catalyst (substance or applied energy) change into other chemicals, and cause the explosive discharge. For that reason, the hydrostatic pressure caused by the water impounded by the dam is aptly called a trigger. Unfortunately, many may assume the "trigger" produced the earthquake, when in fact, pent up stress in the earths crust was the energy source that the "trigger" actuated. Very similar to the powder in the bullet casing exploding causing the gun to fire when the trigger causes the hammer to fall on the detonator. In this region, the movement of tectonic plates continues to build up stress in the earths crust, the release of that stress at this point in time as a result of the hydrostatic pressure may have released stress that could have continued to build to even higher levels before it released and resulted in an even greater magnitude earthquake. In a way, "triggering" earthquakes that otherwise would not have occurred may serve to protect an area from even more devastating earthquakes in the future.
Some years ago scientists were contemplating using hydrostatic pressure along the San Andreas fault in California. The concept was to reduce the hydrostatic pressure at two points some distance apart along the fault line, "locking up" the fault and increase the hydrostatic pressure between the two points, "triggering" a small earthquake in that part of the fault as the hydrostatic pressure acted as a lubricant allowing the rocks on either side to move past each other more easily. Continue the process by leapfrogging along the fault triggering small earthquakes all along the fault. This process would relieve the strain building up as the northwest-bound North American plate moved past the southeast-bound Pacific plate in small segments at a time, avoiding the great earthquake an extensive rupture could cause. In view of the potential cost of failure in such an experiment, it seems to have been put on a back burner.
Triggering vs. Induced