Quantitative Acoustic Emissions Source Mechanisms Analysis of Soft and Competent Rocks through Micromechanics-Seismicity Coupled Modeling

Abstract

This research studied seismic source mechanisms of acoustic emission (AE) events generated during the failure of intact and jointed rock samples using a microscale mechanical-seismicity coupled microscale model. During rock failure, forces and displacements around microcracks were measured in the model to determine seismic moment tensor. Interpretation of AE data was carried out by decomposing the moment tensor into a double couple (DC), a compensated linear vector dipole (CLVD), and isotropic component (ISO). In this study, microscale numerical models of Lac du Bonnet (LDB) granite (intact and jointed) and a Berea sandstone sample were built to represent the mechanical behavior of hard and soft rocks. Subsequently, several numerical triaxial tests under different confining pressures were conducted to analyze source mechanisms of AE events during rock failure. Numerical analysis shows the significant contribution of positive non-DC component during the LDB granite rock failure and significant DC component during the Berea rock failure. The source mechanisms of AE move to the negative non-DC component at higher confining for both granite and sandstone samples. Joint failure causes non-DC component toward crack opening at low confining pressure and a non-DC component toward crack closure events under higher confining pressure. Simulation results, presented in this work, show how micromechanical properties of rocks and joints as well as stress conditions give rise to different types of AE source mechanisms during rock failure.