To investigate microseismic characteristics of fault activation and its deformation mechanism during the excavation of the underground powerhouse, Microseismic (MS) monitoring technique and field survey was adopted. In this paper, the spatiotemporal distribution of microseismicity of fault activation is summarized and presented. In addition, deformation mechanism of fault rupture was revealed during different stages of excavation, and the results showed that fault propagation was associated with excavation and supporting of the first layer of main powerhouse, tensile fracture was main failure mode in this phase. Then, the fault got into the state of rapid unstable propagation in the initial period of stress adjustment before a steady state was realized. Excavation of the second or third layer of main powerhouse was related to fault movement and the degree of fault activation was slight in these two stages.
With regard to fault, internal micro-fractures may often lead to macroscopic instability of fault. Therefore, there must be an intrinsic correlation between fault activation and its internal microseismicity, and it is possible to study fracture or failure processes by analyzing the evolution of internal microfracture (Ge 2005). The MS monitoring technique, as a three-dimensional, real-time monitoring technique, can detect the micro-fracturing signals of rocks and record them as seismograms (Xu et al. 2011). By analyzing the waveforms, the time, spatial locations and source parameters of MS events can be obtained. Tezuka et al. (2000) analyzed the spatial distribution of MS events which were primarily induced by fault activation. Aminzadeh et al. (2013) used tomographic inversion, fuzzy clustering, and shear wave splitting to analyse MS data to obtain reliable characteristics about fractured areas. Based on temporal and spatial distribution of MS events and deformation mechanism, Zhang et al. (2014) analysed fault activation which include the movement and propagation of the fault. Jiang et al. (2010) employed a coupled method which incorporates MS monitoring and numerical simulation to study the tectonic activation. These achievements have proven that the MS technique could be a useful tool for analyzing fracture processes. However, the problem of how to efficiently further utilize the monitored MS data to study the mechanism of evolution of fault activation still urgently needs to be solved.
