The earthquake in Bac Tra My is an earthquake

After nearly a month of survey and research, from November 29 to December 29, the mission consisted of geological and geo-physical experts specializing in natural disasters in the Institute of Science and Vietnam technology, has identified the cause of vibration phenomenon accompanied by explosion in Song Tranh 2 hydropower area, Bac Tra My district, Quang Nam province.

Based on the results of the survey and evaluation of the mission and earthquake monitoring data of the Institute of Geophysics, the Science Council of the Sciences of the Earth, Vietnam Academy of Science and Technology announced. The earthquakes that occurred in the North Tra My area were excited earthquakes.

When the reservoir is filled with water, the lake water load increases the pore water pressure in the breakage zones and thus reduces the shear strength of the rocks in the zone. When the breakage activity is in a critical stress state, reducing the shear strength of the rock in the fracture zone leads to the occurrence of a shear that causes the earthquake to arise. The emergence of stimulated earthquakes by reservoirs is one of the normal phenomenon, local people should not be too concerned.

Song Tranh hydroelectric lake 2

Vietnam has observed the occurrence of stimulating earthquakes with magnitude M = 4.8 at Hoa Binh hydroelectric reservoir after 6-7 months of water storage. Small earthquakes can also be observed up to 4-5 years later with decreasing frequency and magnitude, when stress in the Earth's crust in the area has reached equilibrium, dynamic activity ends, active mode The earthquake in the area will return to the normal tectonic activity mode. The phenomenon of stimulating earthquakes is also observed in many parts of the world, there are special cases of excited earthquakes phenomenon lasting up to 20-40 years such as Koyna Hydroelectricity Lake, India.

Thus, the earthquake data at Hue station shows that the oscillations recorded with S wave amplitude (transverse waves) are much larger than the amplitude of P waves (longitudinal waves) reflecting the vibrations generated in Sliding translation mechanism. Therefore, it can be concluded that vibrations with explosion in Song Tranh 2 area are not related to volcanic activity.

The phenomenon of earthquakes accompanied by explosions is also encountered in many places in Vietnam such as in Dien Bien, Lai Chau, Son La, Cao Bang . in Bac Tra My district, Quang Nam province in the coming time. Similar earthquakes occur even more strongly but will gradually decrease over time and cannot exceed the value of the 5.5 Richter maximum earthquake as assessed before the construction of the Song Tranh 2 hydropower dam.

According to Dr. Tran Tuan Anh, Director of the Geological Institute, to timely monitor earthquake activity in the Song Tranh 2 hydropower area, it is necessary to place an earthquake observation system with 5 seismic stations. Station allocation depends on actual conditions but it is expected that 1 station in the center of Bac Tra My district, 1 dam site and 3 distribution stations around Song Tranh hydroelectric reservoir 2. The distance between stations is about 10 -20km. The observation time of this station network lasts 2-3 years. Such a station system can accurately locate earthquakes in hydropower areas, assessing the development trend of regional earthquake activities.