Microseismics and Geotechnical Applications

AE events in the low frequency range (⟨1 kHz) are sometimes referred to as microseismic activity. In microseismics and geotechnical applications, higher frequency components are preferentially attenuated. The detection of low frequency components can minimize the effect of material inhomogeneity. So far, quantitative treatment of AE in geotechnical fields is limited to the, source location analysis. In the present paper, a source inversion procedure in geologic materials is discussed. The procedure consists of the SiGMA (simplified Green's function for a moment tensor analysis) inversion to determine moment tensor components and the unified decomposition of the eigenvalues to characterize crack types and crack orientations. AE sources are classified into tensile cracks and shear cracks, and crack orientations are determined from the directions of the eigenvectors. As an application, AE events observed in a hydrofracturing test are analyzed. Results show a great promise of AE for clarifying failure mechanisms in geotechnical fields.