In recent years passive high sensitivity seismic techniques have experienced significant technological advancement, and are currently used for monitoring of hydro- and micro-fracture events during stimulated oil recovery and CO2 sequestration sites. Potentially they enable effective tracking of highly localized Acoustic Emission (AE) due to fracture and micro-cracking processes, and detecting fluid flow in fissures and conduits. Our work focuses on relating the AEs to the source mechanisms by computing the moment tensor of events recorded during crack initiation and macroscopic failure around a borehole penetrating a rock sample. The sample is subjected to increasing load in the laboratory using triaxial apparatus and piezo-ceramic receivers to record the emitted AE signals. X-ray Computed Tomography is used after testing to visualize the damage and verify the locations of the AEs. We find that the type of AE source mechanism is more complex than either a pure double couple or a pure mode I tensile crack and includes a combination of the two. In particular, we find that the source mechanisms of events along the borehole are different from events at the macroscopic fracture tip when decomposing the moment tensor into isotropic and deviatoric components.


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