Sat, Feb 07, 2009 - Page 5 News List

FEATURE : Giant reservoir might have caused Sichuan earthquake


The devastating Sichuan Earthquake that killed more than 80,000 people last May might have been partly caused by a huge dam and reservoir, a Chinese expert said.

“The likelihood is very big,” said Fan Xiao (范曉), chief engineer of the investigation team of Sichuan Province’s geological office.

The waters of Zipingpu reservoir, which reach depths of more than 120m, put too much pressure on the geological faults underneath, Fan said. Furthermore, water entering crevices was weakening the rock layers, he said.

Around the world, a number of quakes were caused by dams, experts said. Owing to Zipingpu’s size, holding 1.12 billion cubic meters of water, the likelihood that the reservoir could trigger a quake is estimated around 30 percent to 40 percent.

While the case needed further examination, “the possibility was very big, according to preliminary results,” Fan said.

The danger is not at its height, however, when the reservoir is bursting full.

“It often happens when the water rises or falls quickly,” Fan said.

The reservoir on the Min River filled over the course of two years, but water levels dropped drastically just before May 12. On that tragic day, the earth shook along the Longmenshan fault zone stronger than ever before.

Geophysical hazards scientist Christian Klose of Columbia University said he believed the reservoir’s waters increased the strain on the earth’s crust 25 times more than the tectonic activities.

“Different geophysical observations show that the quake was triggered by changes in tension on the earth’s surface,” Klose said. “The changes in tension were induced by the waters in the Min River valley.”

When the fault ruptured, it moved in the direction in which it was pushed by the pressure emanating from the reservoir.

While the analyses of other Chinese geologists also hinted at the reservoir as a cause of the quake, the thesis that the catastrophe was manmade bears great risks in China, not last because of politics.

Therefore, Fan has been alone in his demands of closer scrutiny of the causes, and said necessary data for analyzing the reservoir’s effects had been suppressed.

“The data are not released,” he said. “The data should be offered to different scientific departments to share. This should be open. But until now it is not.”

After the quake, the dam showed cracks, and probably only its low water levels prevented a catastrophic flooding of the 600,000-inhabitant town of Dujianyan a short distance downriver.

Government statistics say the earthquake damaged 2,830 — mostly small — reservoirs in the region, but in Sichuan alone, at least 69 dams were in danger of breaking.

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