VietNamNet Bridge – Earthquakes and incidents of soil collapse have occurred more frequently near hydropower plant areas in recent months. No detailed conclusions have been made about the cases.

In July, three earthquakes occurred near the Song Tranh 2 hydropower plant area in Quang Nam province. In the Son La and Huoi Quang hydropower plant areas in Son La province, four earthquakes occurred at the same time. Meanwhile, two earthquake accidents occurred in Quang Ngai near the Dak Drink power plant.

A report of the Geophysics Institute showed that four earthquakes measured at 3.4-4.3 on the Richter scale on July 19 and 22. The earthquakes all occurred on the Muong La – Bac Yen zone of faults.

The zone of faults, shown on the geological map, may cause earthquakes in the northwestern part of the country.

Dr. Nguyen Hong Phuong, deputy director of the Center for Earthquake and Tsunami Warning Center, said the earthquakes in Son La are tectonic ones with magnitude of up to 4.3 on the Richter scale, the average magnitude.

However, he said, earthquakes are usually likely to happen on zones of faults, so more earthquakes may happen in Son La. However, it is still impossible to forecast their magnitude.

“There is no clear proof showing the relation between earthquakes and hydropower dams. However, it is still possible that the relation exists,” Phuong said.

“In order to find out if such a relation exists, it is necessary to keep monitoring the reservoirs’ areas to have more reliable figures to analyze,” he added.

According to Dr. Nguyen Truong Tien, chair of the Soil Mechanics and Geotechnical works, when conducting field research before building the Son La hydropower plant, involved parties had arguments about induced earthquakes.

The investor then decided to lower the height of the work in order to reduce the risks. However, arguments about the safety of the dam still continue.

Son La is a big hydropower plant with a reservoir capacity of 10 billion cubic meters and the 230 meter high dam. Therefore, if accidents occur, Hanoi and the North Delta would be inundated under water.

Soon after the earthquakes occurred in the Song Tranh 2 hydropower plant area, a system of 10 monitoring stations were installed by the investor in Bac Tra My area in order to collect figures and give warnings about earthquakes.

According to Dr. Phuong, as there is not enough seismic monitoring stations, many abnormal phenomena in the localities might have been missed.

Therefore, he emphasized the necessity of installing more monitoring stations to find out if there is a relation between hydropower dams and geological accidents.

However, Phuong said the Geophysics Institute only has the function of making scientific research and giving warnings, while it is not an investor.

Phuong had previously told Thua Thien – Hue provincial authorities to install a local monitoring system, after an earthquake occurred in the A Luoi hydropower plant area. However, no system has been set up.

T. Mai