Earthquake hits Three Gorges Dam county

A magnitude-4.7 earthquake hit Zigui county, where the Three Gorges Dam is located on Sunday morning, the second in three days to strike near the world's largest hydropower project in Central China's Hubei province.

The epicenter was about 23 kilometers from the dam and the shake could be felt clearly, the Xinhua News Agency reported.

No casualties were reported in neighboring Badong and Xingshan counties as well as the cities of Shiyan, Xiangyang, Jingmen and Jingzhou, which felt the tremor, the Hubei Earthquake Bureau said.

The China Three Gorges Corporation announced on its official website it was closely monitoring the water plant complex. The quake did not affect dam operations, the Three Gorges Dam construction and operation administrative bureau told Xinhua.

Sunday's quake followed a magnitude-4.3 tremor early Thursday morning about 30 kilometers from the dam.

Zigui and nearby counties are not traditionally associated with earthquakes, according to the historic record. Some 18 earthquakes were recorded in 2003 when the Three Gorges project started operation, the 21st Century Business Herald reported.

Neighboring Badong county had one earthquake in 1,000 years before 1985. Between 2003 and 2011, there have been more than 70 earthquakes of magnitude-2 or stronger, the Beijing-based newspaper reported.

A magnitude-5.1 earthquake hit Badong and Zigui counties on December 16, 2013, injuring three people. The epicenter was 66 kilometers from the dam, Xinhua said.

Chinese experts increasingly support the speculation that the project itself causes local earthquakes.

It was perfectly normal for a large reservoir to cause earthquakes, Liu Shukun, a professor at the China Institute of Water Resources and Hydropower Research, told the Global Times.

"The water is 100 meters deep," Liu said. "Its huge weight exerts massive pressure on the land below. It causes the geological structure to transform or break."

Earthquakes were usually around magnitude 4, he said, with stronger ones rarely recorded. He warned authorities to closely monitor the issue.

Earthquakes happen more frequently during the initial stage of storing water, but decrease or even disappear as time goes by, the China Three Gorges Corporation told China Science Daily.

Chinese Academy of Engineering member Chen Houqun said in January that 100 earthquakes were recorded as caused by dams or reservoirs around the world, a "relatively small number" compared to the tens of thousands of dams globally.

The Three Gorges project is a multi-functional water control system consisting of a 2,309-meter-long and 185-meter-high dam, a five-tier ship lock and 26 hydropower turbo-generators.

The project generates electricity, controls floods by storing excess water and helps regulate the river's shipping capacity.