Overview of the Characteristics of Reservoir-triggered Seismic Activity at Some Hydropower Reservoirs in Vietnam

In this paper, the authors present the expression of triggered earthquakes at some hydropower reservoirs in Vietnam. The results indicate that: (1) The triggered earthquakes of magnitude M > 4.0 have occurred at the Hoa Binh, Song Tranh 2 and Son La hydropower reservoirs. All these reservoirs are more than 90 m deep and located on gneiss, granite or limestone rocks; (2) Triggered earthquakes at the Hoa Binh, Song Tranh 2 and Son La hydropower reservoirs are the rapid ones. The earthquake frequency has close ties with the water level change; (3) Vp/Vs ratio can be used as the main factor determining the triggered earthquake source. The natural earthquake sources interconnecting with the reservoir and having the Vp/Vs ratio of 1.63–1.69 have the highest risk of triggered earthquake occurrence and (4) There is no risk of triggered earthquake occurrence at Hoa Binh hydropower reservoir, the magnitude of 4.9 is the maximum. Triggered earthquakes in the Song Tranh 2 reservoir continue occurring with the magnitude of smaller than 4.7. In the Son La reservoir, triggered earthquakes have a magnitude of 4.3.