[1] 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.

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Risk assessment methods and approaches are useful for environmental planning and decision-making when dealing with risk identification and reduction in a changing global context. This is particularly true for arid and semi-arid regions, such as Siloam village, Limpopo province, South Africa, where it is a common practice to apply fertilisers to the soil during planting season for increasing crop yield. Estimates of vadose zone soil moisture fluxes were used to determine the likelihood of applied agricultural fertilisers to reach the groundwater table. This study combines field observations in the study area and a one-dimensional numerical model to explore the moisture fluxes and their implications for contaminant transport in the vadose zone. Model simulations revealed a lag time of 117 days at topsoil and 913 days beyond the root zone for deep percolation of soluble non-reactive inorganic and organic additives to reach the groundwater table. Preliminary results of this study suggest that the vadose zone is permeable and the groundwater is vulnerable to contamination within the evaluated time scale. Given that disaster risks are inevitable, reasonable methods for control and mitigation of agricultural impacts at this site are highly recommended.