This project proposes to study active rock deformation at depths of 2-4 km in the Western Deep Levels gold mines of the Witwatersrand basin, South Africa. The principal investigator will have wide access to data sets from AngloGold Ltd., the mine operator. The geological structure of the mines is well characterized and the mine operators monitor the details of the mining activities--hence, the mechanism that drives the seismic activity is known as a function of space and time. Monitoring the seismic response will allow examination of the deformation process (e.g., frictional healing), which may yield important information about the applicability of rate-state and other formulations of constitutive relationships. The mining seismologists collect seismic data comprising more than 70 digital, three-component stations, and they process thousands of individual seismic events daily using software (determining seismic moment, corner frequency, radiated energy, as well as location and magnitude). This project will investigate the accuracy of the cataloged parameters, extend the catalogs to include moment tensors, and incorporate algorithms for relative event location and relative moment-tensor determination. These data will be used to a) distinguish events generated by fresh fracturing from those associated with slip on preexisting faults, b) study event sequences, and c) investigate frequency-magnitude distributions and scaling relationships among moment, energy, and corner frequency.
