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 6.0-6.9 seem to occur in 13 seismic sources, these being: Muong Te, Nam Nhe, Muong Nhe, Lai Chau - Dien Bien, Son La, Tuan Giao, Phong Tho, Muong La - Bac Yen, Song Da (Da River), Nam Tong, Mu Cang Chai, Lao Cai - Ninh Binh (Phan Sipan), and Mai Chau. Of these, an apparent risk of strong earthquakes, with 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.

Background seismicity and seismic monitoring in the Lai Chau reservoir area

“…In general, seismic activity in the region of the Lai Chau dam differs from average seismic activity in larger zones including the dam area (e.g. Pailopee and Choowong 2014;Lu et al 2017;Cao et al 2019). Parameters of b value and completeness magnitude obtained in our work seem to be better suited for testing the variability of seismicity caused by filling the reservoir than those discussed above, due to the lower magnitude completeness and a smaller area of the observation.…”

“…Lu et al 2017) or bordering the region of the Lai Chau dam (e.g. Cao et al 2019). All these estimates were obtained with catalogues covering large magnitudes, usually M c = 4.…”