Abstract: Moment tensor method is introduced to analyze rockburst mechanism for deep tunnel, based on microseismic monitoring data of Jinping Ⅱ hydropower station. And some recommendations are proposed for two key issues in the analysis process: ①Restricted by the construction environment in the tunnels, tunnels are excavated in a straight line, and sensors can only be installed at the wall of tunnel or in the shallow boreholes. The calculation reliability of moment tensor is affected greatly on the numerical calculation; the coordinate rotation method is given to improve it. This method rotates the tunnel coordinate system to the new coordinate system, which makes the value of the direction cosine between the source-sensor vector and every coordinate axis less than 10 times, for every waveforms in the event. The ideal results can be got from a large number of moment tensor calculation. ②To get rockburst nucleation process, which calculates the moment tensor firstly, and decompose the moment tensor to the components of basic type, judge the rock fracture type based on the rule from the percentage of the components. But the rule proposed by Ohtsu is only applicable to all components by pulling, which is not suitable to tunnels of fast drilling; therefore, one rule is proposed to extend a more generally applicable state. Lastly, the complete method is established which used to research rockburst nucleation process by the moment tensor method. Analyzed microseismic data of Jinping Ⅱ hydropower station before rockburst happened by this method, the results show that the method can explain the evolution of rock failure mechanism better.

Key words: deep tunnel, microseismic monitoring, moment tensor, rock fracture type, criterion, rockburst nucleation mechanism, Jinping Ⅱ hydropower station