The characteristics of seismic activity in the ladder zone of Da river hydro-electric plants

Abstract

In this paper, the authors describe a study examining the characteristics of seismic activity in the ladder zone of Da river hydro-electric plants. The study results show that: The occurrence of natural earthquakes in the ladder zone of Da river hydro-electric plants is the strongest in Vietnamese territory. An earthquake magnitude of M=6.7 has been observed in the Tuan Giao and Lai Chau areas, with a b coefficient value (Gutenberg-Richter law) of 0.935. Natural earthquakes with magnitudes in the range of 6.W-6.9 seem to occur in 13 seismic sources, these being: Muong Te, Nam Nhe, Muong Nhe, Lai Chau - Dicn Bien, Son La, Tuan Giao, Phong Tho, Muong La - Bac Yen, Song Da (Da River), Nam Tong, Mu Cang Chai, Lao Cai - Ninh Bình (Phan Sipan), and Mai Chau. Of these, an apparent risk of strong earthquakes, w ith a magnitude of M=6.9, appears in Muong Te, Lai Chau - Dien Bien, Tuan Giao, Yen Chau, and Mai Chau areas. Triggered earthquakes with a magnitude M>4.0 have occurred in the region of the Hoa Binh and Son La hydro-electric plant reservoirs, which have a maximum depth of over 100 meters, and a geological structure comprising mainly limestone. No likelihood of triggered earthquakes in the region of the Hoa Binh hydro-electric plant reservoir; however, in the Son La hydro-electric reservoir region, a triggered earthquake is expected in the future with a strong magnitude of M=4.3, or possibly even M=5.0.