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Frequent earthquakes raise fears over Song Tranh Dam

Update: September, 08/2012 - 10:46


A view of the Song Tranh 2 hydropower plant. Earthquakes in the area have raised fears that tremors may cause cracks in the dam. — VNA/VNS Photo Ngoc Ha
HA NOI — Concerns are mounting over the safety of the Song Tranh 2 hydropower plant, after the Bac Tra My District in central Quang Nam Province was struck by a 10th earthquake in four days, sparking fears that the dam could soon be breached.

No one was injured by yesterday's quake but the frequency of the tremors is a growing cause for concern. Measuring just under 4 on the Richter scale, it was nearly as potent as the 4.2 Richter earthquake which rocked the area on Monday evening.

With a seismic focus at the depth of 7.3km, Monday's earthquake was the strongest of the 10 measured so far, however locals now fear it is only a matter of time before further damage is done.

Dang Phong, chairman of the district's people's committee said the safety concerns have caused many people to flee their homes.

He said local authorities have updated residents on the situation and are taking preventive measures to mitigate losses.

Nguyen Hong Phuong, deputy director of the Earthquake and Tsunami Warning Centre at the Institute of Geophysics said the hydropower plant was safe because the dam was designed to withstand a 5.5 Richter earthquake.

But he warned that the tremors and earthquakes have been becoming increasingly powerful.

According to the institute, the earthquakes possibly resulted from instabilities in shear zones Tra Bong, Hung Nhuong – Ta Vi within Song Tranh 2 hydropower plant reservoir.

Meanwhile, Dr Nguyen Dinh Xuyen, an expert in geophysics said the sequence of earthquakes in this area, which started at the end of last year, were happening according to the rule of earthquake excitation by the water storage of the hydropower plant reservoir.

"This means the water storage of the reservoir at a specific level will trigger a sequence of earthquakes and tremors. This sequence will come to an end when the strongest earthquake strikes, which as a rule never exceeds the reservoir's design limit," he said.

He added: "This sequence is yet to end but is forecasted not to go beyond 5-5.5 Richter. It may last for several years."

He warned that earthquakes of five and above on the scale have the potential to destroy nearby houses.

Xuyen added: "This situation is similar to that at the Hoa Binh Hydropower Plant in 1989 when the water storage level reached 85 metres and a sequence of earthquakes with stronger acceleration hit the region. The five Richter earthquake, the strongest one of the sequence, struck two years later. This was followed by weaker earthquakes which eventually ceased after a five-year sequence."

Experts called for earthquake observation stations to be set up to provide specific long-term data, so that the consequences of future earthquakes can be accurately predicted.

Four stations within Song Tranh dam are planned and would be able to record and analyse key data when an earthquake strikes.

Phuong said the institute's experts began a 10-day inspection of the area in a bid to draw final conclusions about the causes and patterns of the earthquakes.

The Ministry of Science and Technology has announced it would conduct detailed study of the geology and dynamics of Bac Tra My District next year. — VNS

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