Mechanism of loud sound in a powerhouse during operation of a hydropower station based on microseismic monitoring

The main objective of this study is to investigate the mechanism of loud sound (LS) events encountered in a powerhouse during the operational period of a hydropower station in Southwest China and to analyze the statistical characteristics and potential predisposing factors. For this purpose, a microseismic monitoring system surrounding the rock mass of the powerhouse is established to obtain information about the microseismic (MS) events of rock mass rupture; this information is used to plot the cloud map of the source parameter and the relationship between the magnitude and frequency. In addition, the moment tensor inversion theory is introduced to invert the rupture mechanism of the MS event in the process of LS events and reveal the relationship between the MS activity and LS events. The results show that the LS event is induced by fault instability under the coupling of multiple factors such as the near-field earthquake, geological defects surrounding the station, water inflow in the mountain, and in situ stress field. Near-field earthquake disturbances are the major cause of LS events. Geological defects, such as faults and joints, are a concentrating distribution area for MS events. The evolution of water inflow over time is similar to that of the frequency of all MS events and has some degree of influence on the occurrence of LS events. This research explores the mechanism of LS events in a hydropower station and provides a reference for identifying potential hazard sources in underground structures during their operational period.