Abstract:

This paper presents the risk assessment of triggered earthquake in the quarries Thuong Tan III, IV after exploiting 100 m depth and impounding water for landscaped lake. Combination methods of gravity and electromagnetotelluric were used to estimate fault parameters, as well as fault segmentation method, was used to estimate the risk of the maximum magnitude of natural and triggered earthquake. Further, these fault parameters are considered as input information to computing the influence of the Thuong Tan III, IV reservoir impoundment by using the concept of fault stability Coulomb stress in order to assess the risk of triggered earthquake occurrence. The results show that: The quarries Thuong Tan III, IV are within the sphere of influence of second-order active fault Thien Tan - Binh Son. Triggered earthquake source has a length and width of 4.8 km and 1.8 km, respectively, with Strike angle = 1400, Dip angle = 800 and Rake angle = 1800. The maximum magnitude of natural earthquake in this source is 5.0 while that of the triggered earthquake is smaller than 3.2. The peak ground acceleration caused by triggered earthquake M = 3.2 in the lake Thuong Tan III, IV is 30.809 cm/s2, corresponding to the vibration oflevel V (MSK- 64, approximately 0.0308 g). With this vibration level, many people can feel the earthquake. Some unstable objects are overturned or moved. The Coulomb stress field at 2 km depth can reach the maximum value of 9.485 kPa. The region of positive Coulomb stress shows the influence of reservoir impoundment indicating the region of risk of triggered earthquakes occurrence.