Analysis of the Seismic Moment Tensor of Acoustic Emission: Granite Fracture Micromechanisms During Three-Point Bending

Abstract

An experimental study of granite fracture micromechanisms during three-point bending based on reconstruction of the seismic moment tensor components for acoustic emission events has been carried out. An original three-stage algorithm for refining and rejecting solutions for the seismic moment tensor of acoustic emission events is proposed, based on a hybrid iterative algorithm and the jackknife resampling method. After the formation of a catalog of acoustic emission events with a stable solution, their mechanisms were analyzed. It is shown that in the case of three-point bending of granite, acoustic emission events are localized in the zone of formation of the future main crack. It has been found that granite bending is accompanied by the formation and development of normal opening cracks with an additional shear component of varying intensity. The kinematics of the found mechanisms of acoustic emission events corresponds to the configuration of loads applied to the sample. The shear component is caused by the microstructural inhomogeneity of the sample. Variations in the orientations of the axes of maximum deviatoric compression (P-axis) and tension (T-axis) are determined, which are associated with the variability of the local stress-strain state of the material near acoustic emission sources. It is shown that the instantaneous magnitudes of acoustic emission events obey the Gutenberg–Richter law.