Assessment on maximum magnitude of natural and triggered earthquake when water is impounded in the mining pit: A case study in Nui Nho quarry, Vietnam based on gravity and magnetic data

The paper presents the assessment of the maximum magnitude of natural and triggered earthquakes when water is impounded to 130 m in the mining pit for the landscaped lake in the Nui Nho quarry in Di An commune, Binh Duong province, Vietnam. The maximum magnitudes of the natural and triggered earthquakes were estimated by using artificial neural network and source segmentation methods, respectively. Gravity method was used to estimate fault parameters including strike, dip and rake angles. As well as, these fault parameters are considered as input information to compute the influence of Nui Nho reservoir impoundment by using the concept of fault stability Coulomb stress in order to assess risk of triggered earthquake occurrence. The results show that the Nui Nho quarry is within the sphere of influence of second order Dong Nai River fault zone; the magnitude of natural earthquake that can occur in this area is 5.0; the triggered earthquake source of Nui Nho lake has the length of 4.8 km and the width of 1.8 km; the maximum magnitude of triggered earthquake can only be less than or equal to 3.2; the reservoir with depth of 130 m can cause direct stress on the lake bottom with the maximum value of 47.295 kPa and Coulomb stress field with the value of 4.338 kPa. The region of positive Coulomb stress shows the influence of reservoir impoundment indicating the region of risk of triggered earthquakes occurrence. KEYWORDS: Quarry; Nui Nho; natural earthquake; triggered earthquake; artificial neural network; incremental stress; Coulomb stress. © 2020 by the Geophysical Center RAS.