For the first time applying modern statistical methods, the study of stimulated earthquakes occurring near hydroelectric dams
In Vietnam, stimulated earthquakes have occurred at some reservoirs after accumulating water such as Hoa Binh, Son La and Lai Chau. Especially, in Song Tranh 2 hydropower area, the earthquake showed signs of abnormal activity when regular activity continue from 2011 until now with no signs of abating. Song Tranh 2 hydropower was stored in November 2010, soon after which earthquakes began to occurappear near the lake. Earthquake manifestations have increased since 2011, especially two earthquakes with M = 4.6 and 4.7 occurred on October 22 and November 15, 2012, causing minor damage to houses in Bac Tra My district. To understand the situation, the research team conducted a detailed study to clarify the dynamic process caused by the change in the lake level affecting earthquake activity stimulating the Song Tranh 2 hydropower area.
Map of the study site and earthquake epicenter (ML ≥ 1) of Song Tranh 2 hydropower area from September 2012 to March 2020
The relationship between earthquake activity and reservoir level changes between October 2011 and March 2020
To solve the set objectives, the project has chosen to use a combination of research methods including: Method of solving the seismic tensor reverse problem to study earthquake seismic mechanisms; Simulation method for changes in Coulomb stress field and pore pressure due to reservoir water accumulation to study the mechanism of stimulated earthquake generation; Some modern statistical methods such as the nearest neighbor method; The method of spectral analysis of the sequence of earthquakes and changes in lake level is aimed at finding the main period of earthquake activity.
The study identified the seismic mechanism of 21 earthquakes with a right-sided sliding mechanism with a slope angle between 50o and 77o. The compressive stress axis (P) is northwest-southeast, and northeast-southwest.
The results of Coulomb stress simulations show that the majority of earthquakes occur in the positive value zone of ∆S, meaning that the reservoir's water accumulation has an effect on the occurrence of earthquakes. The results of Schuster spectroscopic analysis have determined that the main cycle of earthquake activity of Song Tranh 2 hydropower area is about 390 days, this result is consistent with the main cycle of water accumulation. The study results support the conclusion that the reservoir water accumulation cycle is a factor driving the ongoing seismic activity in the Song Tranh 2 hydropower reservoir area.
The application of modern methods to study the mechanism of occurrence and the law of earthquake occurrence has profound scientific and practical significance. This is the first time modern statistical methods have been applied in the study of seismicity and the law of earthquake occurrence in Song Tranh 2 in particular and in Vietnam in general. The results of the project will create a new direction and new approach in reservoir stimulated earthquake research, which is a premise for further research on stimulated earthquakes for other reservoirs in Vietnam. The results of the project will be handed over to research units, disaster prevention and mitigation units, the Ministry of Industry and Trade, Song Tranh 2 hydropower plant and relevant agencies, contributing to research on disaster warning and mitigation.
Translated by Phuong Ha
Link to Vietnamese version
