The May 2008 Wenchuan earthquake (Mw 7.9) which killed almost 90,000 people and buried whole villages with landslides may have been triggered by the filling of the Zipingpu reservoir behind a high dam. Detailed analysis of the stress field around the fault zone shows that the weight of the water combined with the increase in pore pressure caused by the 100 meter deep reservoir was large enough to induce an earthquake hundreds of years before it would have happened without the reservoir.
By FishOutofWater
The Zipingpu Reservoir, is located close to the Yingxiu-Beichuan (YB) fault and a few kilometers west of the Guanxian-Anxian (GA) fault, both which ruptured during the Wenchuan earthquake. Reservoir filling began in September 2005, going up 120 meters to the maximum level in one year.
By FishOutofWater
The weight of the reservoir affected the static stress field within one year, but the increase in pore pressure caused by the high column of water, diffused downward more slowly.
By FishOutofWater
The change in effective Coulomb stress (Figure 3c) is obtained by summing the changes due to static loading (Figure 3a) and hydrodynamic diffusion (Figure 3b). Although the spatial pattern of the effective Coulomb stress changes is similar to that caused by the static loading (Figure 3a), the values are augmented by the positive pore pressure values shown in Figure 3b. At 2.7 years after the impoundment of the Zipingpu Reservoir, changes of more than ±0.01 MPa are observed in a region extending 20 km west and 20 km below the reservoir. Such changes are comparable in magnitude to those induced by large earthquakes and that have been shown to trigger or delay subsequent earthquakes [Reasenberg and Simpson, 1992; Stein, 1999], and to the coseismic Coulomb stress changes by the Wenchuan Earthquake [Parsons et al., 2008; Toda et al., 2008].
Human activities that increase pore pressures, such as hot dry rock geothermal injection of water have been known to cause small earthquakes. Reservoirs, such as the Oroville Dam in California are suspected to have triggered earthquakes. There have been discussion going on for many years about the seismic safety of the 610 feet high and 1.3 miles wide 3 Gorges Dam which is now being filled in China. It is designed to withstand a M7.0 earthquake, but not a M7.9 like the Wenchuan earthquake.
The Three Gorges Dam will be higher and will store 5 times more water than the Zipingu Reservoir.
Stress changes caused by the Zipingu Reservoir on the Yingxiu-Beichuan fault.
By FishOutofWater
This study has implications for any activity that causes significant stress changes in a seismically active region. Both the U.S. and China are planning CO2 sequestration, the injection of pressurized CO2 into the ground. In most of China and much of the U.S. pressurized fluids may trigger earthquakes. Spent and declining oil and gas fields have the capacity to take up only a small fraction of the CO2 being generated in the U.S. and China. Much of China and much of the western United States are poorly suited to carbon sequestration because earthquakes might be triggered and because long-term CO2 storage cannot be assured.
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