Accurate moment tensor inversion of acoustic emissions and its application to Brazilian splitting test

The efficiency of three inversions for accurate moment tensors: (1) the standard least-squares inversion, (2) the weighted least-squares inversion, and (3) the shear-tensile-compressive (STC) source inversion, is tested on acoustic emissions (AEs) produced during the Brazilian splitting test. A comparison of plots of the P/T axes of the focal mechanisms reveals that the double-couple part of the moment tensors is well constrained for all three inversions. By contrast, diamond source-type plots show that the non-double-couple components of the retrieved moment tensors are more sensitive to errors due to neglecting inhomogeneities and anisotropy in the rock sample, near-field terms and other wave phenomena effects. The weighted inversion and the STC inversion work better than the standard least-squares method and yield less scattered results. If moment tensors of AEs contain significant non-double-couple components of moment tensors produced by non-shear fracturing, the STC inversion proved to be most accurate. The retrieved moment tensors are well consistent with the expected fracture mechanism of AEs in the Brazilian splitting specimen and provide a further guidance for studying rock fracture processes.