The Song Tranh 2 Hydropower Plant in Bac Tra My District, Quang Nam Province. The plant, which opened last December, is suspected of causing underground explosions and minor earthquakes in the district
The Ministry of Science and Technology began Wednesday (November 30) a seismic survey in the central province of Quang Nam in response to local authorities' call for help in understanding unidentified underground explosion sounds and tremors that have terrified residents since the end of last year.
The survey is scheduled to be done over ten days in Bac Tra My and Nam Tra My districts.
On Monday, in a letter to the ministry and the Vietnam Academy of Science and Technology, Tran Minh Ca, vice chairman of Quang Nam's People's Committee, the local government, said the situation was getting worse in Bac Tra My District.
Ca said the district first recorded tremors in January, and they became stronger in June, adding that on November 16-17, locals heard many explosions underground.
Tremors and explosions have since occurred more frequently and strongly, shaking and damaging houses, Ca said.
Le Huy Minh, director of the Center for Earthquake Information and Tsunami Forecasting at the Vietnam Institute of Geophysics, said four quakes with magnitudes of between 1.9 and 3.3 on the Richter scale had struck the district last month.
"The problem has panicked and worried locals, and affected their lives," Ca said, requesting that the ministry and the academy study the phenomenon and solve it as soon as possible.
Meanwhile, in an interview with Thanh Nien, Dang Phong, chairman of Bac Tra My District's People's Committee, said everyone could feel the tremors, especially people who live on hills.
"My bed, which is placed next to the wall, hit it continuously. Moreover, other things like tables, chairs and wardrobes also moved as the tremors happened," Phong said.
Hydropower plant suspected
Several officials and experts suspect that the phenomenon is related to the Song Tranh 2 Hydropower Plant that stands in the vicinity.
Minh said it is probably induced seismicity, which refers to minor earthquakes caused by human activities that change the Earth's crust, because the recorded quakes' seismic depth was between three and five kilometers, which was shallower than most earthquakes that have hit Vietnam.
Moreover, the tremors at Bac Tra My District happened after the plant's reservoir went into operation in December last year, he said.
But further observation and study is needed to arrive at comprehensive conclusions, the official said.
Cao Dinh Trieu, vice chairman of the Vietnam Association of Geophysicists, also blamed the operation of Song Tranh 2's hydropower dam.
According to Trieu, the earthquakes might have occurred as water in the dam's reservoir had been absorbed by the fault zones in the area, causing seismic waves. Because the quakes happened at shallow depths, explosion sounds could be heard, he added.
He said dam-induced seismicity only happens when a dam has a height of more than 80 meters, is located in a fracture zone, and its reservoir's capacity is more than one billion cubic meters.
The phenomenon has been recorded many times in the world, and some of them have been of massive magnitudes, causing losses of human lives and property, the scientist said.
In Vietnam, an earthquake of 4.7-magnitude was recorded in 1989 after the Hoa Binh hydropower plant in the northern eponymous province began operations, Trieu said.
However, he told people not to be too worried, noting that scientists were starting to study the phenomenon and have proposed at least three observation stations around the Song Tranh 2 area to keep track of quakes.
The Song Tranh 2 hydropower plant was built with an investment of more than VND4.15 trillion (US$197.53 million). It started operations in December last year with an expected output of 190 megawatts.
The plant made headlines last month, along with other hydropower plants in the region, for worsening the danger and impacts of floods by releasing water from its reservoir.