Source parameters and focal mechanism of ruptures in coal and sandstone specimens under uniaxial loading based on acoustic emission signals

Abstract To investigate the source properties and focal mechanism of coal and sandstone specimen rupture under uniaxial loading, acoustic emission (AE) testing of sandstone and coal specimen rupture under uniaxial loading was conducted. The spatio-temporal evolution of AE parameters in the rupture process was determined through the AE testing of coal and sandstone specimen rupture under uniaxial loading. The source parameters of sandstone and coal specimen rupture were then calculated and analyzed using the Brune model and grid-search method. Finally, the focal mechanism of sandstone and coal specimen rupture was deduced by inversion and compared based on source parameters and moment tensor inversion. The results show that: the rupture morphology of sandstone specimens differs from that of coal specimens; the source displacement spectra of sandstone and coal specimens under uniaxial loading are in good agreement with the Brune model. The corner frequency of coal and sandstone specimens decreases linearly with the increase of seismic moment; source radius and energy increase linearly with increasing seismic moment; the stress-drop fluctuates around a certain value. For events of the same magnitude, the corner frequency, energy, and source radius of sandstone specimens at rupture are greater than those of coal specimens at rupture, but the stress-drop in sandstone specimens (at rupture) is smaller than that occurring in coal specimens. In the middle and early stages of rupture, the coal and sandstone specimens mainly undergo shear failure. Shear-tension and shear-compression failures occur in the later stage of rupture. These results can be used to quantify and evaluate the source properties and focal mechanism of small-scale specimens at rupture.