| Microseismic monitoring technology has been widely used in engineering in recent years.At the same time,the understanding of rock mass fracture mechanism and the study of focal mechanism solution theory in microseismic are also hot and difficult issues in the current research field,which need to be further studied.Meanwhile,the research on the practical application of focal mechanism and stress state inversion of rock mass fracture in the microseismic monitoring engineering is also a key issue that the researchers are concerned about.Starting from the concept of focal mechanism and the concept of fault plane parameters,this paper studies the method of moment tensor inversion to solve focal mechanism.In this paper,the method of moment tensor decomposition is mainly studied,and then the three parameters(strike,dip angle and slip angle)of the fault plane can be solved by pure dual couple component.Based on this,the graphic expression of focal mechanism which means focal beach ball diagram and the diamond source type plot are studied.The study of theoretical method of using the focal mechanism to solve the inversion stress field is another main research field of this paper.The Wallace-Bott hypothesis is used as the basic starting point to explore the basic principles of stress inversion.Three basic stress inversion methods are studied and their characteristics are compared and analyzed.More importantly,the iterative joint inversion method for stress and fault orientations from focal mechanisms is introduced.This method is applied to the linear inversion method by adding the instability coefficient as the constraint,to improve the accuracy of the inversion results.This paper also carried out the analysis of the geometric occurrence of the focal fracture surface based on the principal component analysis(PCA).The case used is the large slide failure caused by the aftershock of artificial blasting of Shizhuyuan Polymetallic Mine,and 39 valuable spatial coordinates of positioning events were recorded by the microseismic system,the strike and dip of the focal fracture in the area are calculated,and the potential slip surface map of the event group was drawn.The comparison shows that the PCA can provide a more reliable and rapid analysis method for determining the geometric occurrence of the focal fracture surface.In view of the theoretical application problems in the practical microseismic monitoring engineering,based on the theories of moment tensor inversion and iterative joint inversion stress method,Jiangxi Xianglushan tungsten mine was recorded through the microseismic monitoring and positioning system on October 27,2018.The 17 sets of positioning events were carried out.First,the moment tensor inversion of focal mechanism method was studied.The focal fault parameters are calculated and focal beach ball plots are drawn.According to the relationship between the moment tensor components and the drawing of the source type map,we can distinguish the source fracture types of this case,and draw the conclusion that the larger probability is the mixed fracture of tension compression and shear.Then,by inputting the fault parameters of each source,the stress state of the source area is analyzed,the directions of the three principal stresses and the distribution of the P-T axis and the principal stress axis of the fracture surface of the source are obtained by the iterative joint inversion method,and the feasibility of this engineering application is higher by combining the analysis of the stress Mohr circle distribution diagram,and the strike of the two nodal planes of the main fault surface can be calculated Inclination and slip angle.Considering two different engineering cases,PCA analysis,focal mechanism and stress inversion are carried out respectively.According to different engineering situations,the applicability of the theory studied in this paper in different working conditions is discussed. |
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