(April 9, 2014) Another earthquake has struck China’s seismically hazardous southwestern region in the same vicinity as one of the country’s mega-dams. Chinese geologist and environmentalist Fan Xiao says there is a “high probability” the Xiluodu dam, China’s second and the world’s third biggest hydropower plant, triggered the quake.

A 5.4-magnitude earthquake jolted Yongshan County in Yunnan province on Saturday, April 5, at 6:40 a.m. (local time) in Xiluodu township at a depth of 26 kilometres, striking an area shared by China’s second largest dam on the upper reaches of the Yangtze River, seven kilometres from the quake’s epicentre.

The 13.86GW Xiluodu hydropower plant located near Xiluodu Town, the county seat of Yunnan’s Yongshan County.

Details reported by the US Geological Survey, as  above, differ from the China Earthquake Networks Center which put the depth of the quake at 13 kilometres with a magnitude of 5.3.

Reports by Chinese state media say the Saturday event injured at least 10 people, two seriously; damaged at least 20 buildings and blocked roads, due to falling rocks in mountainous parts of the region.

High-profile Chinese geologist and environmentalist Fan Xiao — former chief engineer of the Regional Geology Investigation Team of the Sichuan Geology and Mineral Bureau — told Probe International that, based on the time and spatial characteristics of the quake, the probability was high that its cause pointed to the Xiluodu dam reservoir as it approached its first high-water mark.

Reservoir impoundment exerts great pressure on existing fractures and fault lines, particularly in the years after a dam reservoir is filled to its highest level, due to the time it takes for reservoir water to penetrate deep into seismic faults and fissures before it triggers seismic activity. Sharply rising or rapidly falling reservoir water levels pose a threat to geological stability and can trigger disaster.

According to Fan Xiao, impoundment of Xiluodu began in May 2013, reaching 560 metres with an increase of 120 metres over the last year. It is currently at its lowest level in anticipation of the region’s wet season. The dam operator plans to raise the reservoir’s water level to its normal pool level of 600 metres (above sea level) in August 2014.

Although, the effect of the earthquake on the Xiluodu dam itself was not substantial, damage to civilian structures however was, reports Mr. Fan, who says the region can expect more seismic disruption as a result of reservoir-induced seismicity (RIS).

RIS, he says, occurs when a dam reservoir’s water level reaches its highest point. Given that Xiluodu is on its way to reaching that mark, the next several years will be the most potentially hazardous for the surrounding region, he says.

In late July of last year, Mr. Fan revealed that analysis of a giant landslide in the same province as Saturday’s 5.4M earthquake indicated that impoundment of the nearby Xiluodu dam reservoir was most likely the cause of that event. At the time, he said more incidents could be expected when the reservoir, with an estimated capacity of 12.67 billion cubic metres, was filled again.

A rash of earthquakes have struck quake-prone southwestern China in recent times, including a magnitude-7 earthquake that hit Lushan County in April 2013, which killed more than 200 people and left thousands injured and tens of thousands homeless. Mr. Fan contends that quake may be an aftershock of the deadly 2008 magnitude-8 Wenchuan earthquake, one of the world’s worst disasters and an event he investigated in Did the Zipingpu Dam Trigger China’s 2008 Earthquake? The Scientific Case, which he linked to the dam’s impounding activities since 2008.

Time line of impoundment for the Xiluodu Dam:

May 4, 2013: Impoundment begins and the reservoir reaches a water level of 440 metres.

June 15, 2014: The reservoir is filled to 524 metres.

June 23, 2013: The reservoir is filled to 540 metres as the first phase of impoundment is completed.

December 8, 2013: The second phase of impoundment is completed as the reservoir is filled to 560 metres.

Currently, the Xiluodu’s water level is dropping and is currently lower than 560 metres.

The third phase of impoundment is set to begin in late August of this year when the reservoir will fill to its normal pool level of 600 metres (above sea level).

Further Reading:

Fan Xiao | Probe International
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