Yang: 【5】Earthquakes

Sichuan Earthquake map

       
         
A possible threat affecting society mentally is not the only concern. The weight of millions of tons of water behind a dam can increase the chances of an earthquake. With any minor effects of an earthquake, the dam is subjected to breaking or severe landslides can occur. If the dam were to break, this would cause a major flooding of the Yangtze delta. The destroying of the dam would wash away millions of people into the sea while destroying all viable land surrounding the river. Back in 1975, in Southern Henan Province, heavy rains caused a break in a chain of dams (Jhaveri, 1988). Millions of people below the dam were washed away into the Pacific Ocean and the remaining lives were left homeless. Other cases of dam breaks were reported in USA, Italy, and many other countries.

Two scientists at the Geophysical Institute are working together to help the Chinese assess the earthquake risk of Three Gorges Dam. Born in the mountains of the Tibetan Plateau, the Yangtze River flows almost 4,000 miles to the ocean, making it the third longest river in the world after the Nile and the Amazon (the Yukon is half the length of the Yangtze). Hoping to harness the power of the river, the Chinese government began building the dam a few years ago, expecting to finish by 2009. When the mile-wide, 600-foot high dam is complete, the flooding upstream will begin. As the water rises, it will drown more than 1,400 rural towns and villages abandoned earlier by government decree. The water rising behind the dam will power 26 huge turbines to provide electricity, and will allow people to control a river that has killed 300,000 people by flooding during the 20th century.
       

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.)

The biggest fear of all is a dam breach. The dam’s failure would result in one of the worst disasters in history. Some 75 million people live directly downstream of Three Gorges. No one knows how local seismic faults will react to the incredible mass of water behind Three Gorges Dam. Like heavy snow on an overloaded roof, the weight of water blocked by dams can cause existing cracks in Earth's crust to slip, resulting in earthquakes. Faults tend to slip more often when a nearby giant reservoir is filled with water.

Reference: 
Jhaveri, Nayna. 1988. "The Three Gorges Debacle." The Ecologist 18:56-63. 
Giant Chinese Dam May Cause Earth to Move, Alaska Science Forum." Giant Chinese Dam May Cause Earth to Move, Alaska Science Forum. <http://www2.gi.alaska.edu/ScienceForum/ASF14/1465.html>.

Birchard, George. "Daily Kos." Deadly M7.9 China Earthquake Triggered by Reservoir. <http://www.dailykos.com/story/2009/11/11/803536/-Deadly-M7-9-China-Earthquake-Triggered-by-Reservoir>.