Source parameters of acoustic emission events and scaling with mining-induced seismicity

Abstract

A series of uniaxial compression tests were performed on 96-mm-diameter quartzite samples, 242 mm in length, to understand the scaling of rock fracture processes. Nine acoustic emission (AE) sensors glued to each sample monitored the AEs resulting from microcracking within the samples. In contrast to previous AE studies, the sensors were calibrated as velocity transducers so that the output could be compared to mining-induced seismicity and natural earthquakes. A new hybrid, relative moment tensor method was applied to obtain source mechanism solutions for eight clusters of events. Once the AE rate accelerated prior to failure, the event positions are associated with the observed failure planes. The moment tensors were found to have double-couple components, indicating that shearing was occurring. The stress drop appears to be constant over the range of moments suggesting the self-similar scaling of the fracture response from the laboratory sample to mine seismicity and natural earthquakes over a wide range of length scales. Similar conclusions can be drawn by considering the apparent stress and source radius. The scaling of the peak velocity and peak acceleration parameters is apparently consistent with mining-induced seismicity but is considerably affected by high-frequency attenuation and the limited bandwidth. This is confirmed by the frequency-magnitude plot, which has a slope of unity. The fracture processes in the laboratory are similar to those occurring underground near stope faces and pillars in deep-level South African gold mines, where there is a high vertical compression and low confinement.