Abstract: In order to carry out the research on the focal mechanism solution of rock mass microseisms, the analysis is based on the moment tensor theory. In view of the limitations that the Ohtsu’s decomposition method and the rock mass fracture type criterion are only suitable for the rock mass under tension conditions, the moment tensor decomposition model of the rock mass under compression is adopted. By discussing the positive and negative of the compensated linear vector dipole (CLVD) component, the component calculation expression is improved and the isotropic (ISO) component is introduced to modify the rock fracture type criterion; meanwhile, the CLVD-ISO diamond source type map is adopted to illustrate the characteristics of various rock mass fracture types. Besides, the tension source model is adopted for characterizing the fracture surface occurrence with the deficiencies of the double-couple (DC) component (MDC) taken into considered. On this basis, the analyses of focal, including the source mechanism, the mechanical mechanism and the spatial distribution characteristics of the source fracture surface are carried out combined with a typical engineering case of Xianglushan Tungsten Mine. Based on the modified criterion, the results indicate that the main types of rock mass fracture in this case are tension fracture and compression fracture. Furthermore, the special distribution of source fracture surface parameters are obtained with the tension source model adopted. The analysis results are basically consistent with that in actual situations, which also verify the application of the improved model in the focal mechanism solution analysis of engineering microseisms based on the moment tensor theory.

Key words: microseismic monitoring, focal mechanism, moment tensor theory, rock mass fracture type, fracture surface occurrence