## 1 Introduction
[19] introduced microseismic monitoring into the Huijahe Coal Mine, Binchang Mining Area, Shaanxi, and proposed a comprehensive warning model for rock bursts based on the microseismic precursor indicator system; and [PERSON] et al. [20] adopted microseismic monitoring to trace and evaluate fractures in hydraulic fracturing of coal seams. In recent years, hydropower stations have been built in Southwest China to provide energy support for national development. Due to complex geological conditions and frequent occurrence of various engineering and geological disasters, microseismic monitoring has been gradually applied to the hydropower industry, providing a new method to ensure construction safety. [PERSON] et al. [22; 23] applied microseismic monitoring to Jinping-II hydropower station to study microseismic activities, TBM boring, and the occurrence of rock bursts, and predict or forecast the occurrence of rock bursts during TBM boring in deep-buried tunnels; [PERSON] et al. [24] used the microseismic monitoring system to obtain the source information and applied the loading/unloading response ratio theory to predict the slope failure during water storage in the Dagangshan hydropower station; [PERSON] et al. [25] studied and predicted the hazard of rock bursts in the tunnel of the Jinping-II hydropower station using microseismic monitoring, indicating that the technology can be used to capture seismic activities in the stress formation and warning period; [PERSON] et al. [26; 27; 28] carried out microseismic monitoring in the Jinping-I, Shuangjiangkou, and Houziyan hydropower stations, studied the evolution process of microfractures and the formation process of rock deformation inside the surrounding rock in blasting and excavation based on the monitoring results, and gave a warning or forecast, thus ensuring the site construction safety. The deformation and failure of hydraulic tunnels is usually affected by various factors, such as the geostress, excavation unloading, and geological structure. The failure evolution mechanism of the rock mass dominated by different factors is the basis of the stability analysis. In this study, a microseismic monitoring system was established in the diversion tunnel of a hydropower station. Based on the spatial and temporal characteristics of microseismic activities during the excavation, the main damage areas of the rock mass were delineated. Under the site construction and geological conditions, the main factors causing damage to rock mass were revealed. The characteristics of the microseismic source parameters in typical periods were analyzed. The damage evolution mechanism was discussed. Finally, a 3D numerical model of the multi-discontinuous tunnel areas was established and compared with the microseismic monitoring results. It is worth noting that three structural planes with different combination types appear in a short tunnel. Secondly, microseismic monitoring technology is used to track the fracture damage of surrounding rock in this section, and numerical calculation model is used to verify it. The results reveal which type of combined structure has the greatest influence on the tunnel. The research results can provide a better understanding of the rock mass fracturing mechanism and failures of this hydraulic tunnel and other similar tunnels.