This paper presents the application of Digital Elevation Model (DEM) for mapping seismic zones in Cao Bang province and adjacent areas. The application of the Analytic Hierarchy Process (AHP) in this study consists of four analytical steps namely: (1) Determination of the geomorphic indices' sensitivity with respect to the earthquake activity using the MLP (Multi-layer Perceptron) neural network; (2) Calculation of the weight coefficients of all indices according to principle Eigenvector (AHP method); (3) Estimation of the ranking sensitivity of each geomorphic indices to the earthquake activity using their value distribution and (4) Identification of the Seismic Susceptibility Index (SSI). The results show that there are 6 seismic zones in the study area, including Na Hang, where the largest earthquake occurred with M4.

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.

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