3. Electronic Theses and Dissertations (ETDs) - All submissions

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    Predicting the effects of explosions placed on the earth's surface
    (2020) Grobbelaar, Michelle Robyn Garvin
    Many predictive equations within literature are focused on explosions within the ground such as mining blasts and tunnelling. According to the United States Code of Federal Regulations (30 CFR part 816.67 of 1998), the recommended equipment to monitor buried explosions, are geophones. Other equations which examine surface explosions utilise a number of specialised equipment in addition to the seismograph equipment used for monitoring buried explosions, such as microphones and pressure gauges. The aim of this study is to determine whether or not one could use predictive equations for buried explosions to predict the effects from surface explosions by merely using data obtained from a small network of surface installed seismograph stations. Military demolition sites are areas where old and potentially unstable explosives and obsolete equipment are destroyed and the ordnance is placed on the surface of the ground and detonated. The ordnance is seldom buried and thus modelling and predicting the ground vibrations and shock waves should consider predictive equations for both ground waves and atmospheric shock waves. The modelling can assist in preventing damages to surrounding infrastructure and injury to people in the vicinity. These equations could similarly be utilised for assisting in forensic seismology to determine the details of unexpected explosions, such as gas pipelines, silo explosions and vehicle bombs. By combining the various equations available, this study has identified a number of predictive equations which have produced acceptable results when examining data obtained from military ordnance demolitions on the surface. In general, the values for atmospheric shock waves are easier to determine than those from the ground motion because the atmospheric shock waves are more prominent on the seismograms than those of the ground motion, due to the fact that very little of the energy is transmitted into the ground. Therefore, utilising atmospheric shock wave measurements may be more useful because the ground motion waves are not clearly recorded. The study has shown that the USBM peak particle velocity (PPV) predictive
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    Enhance South deep variography by including flat inclined boreholes in the local direct estimation methodology
    (2018) Mutobvu, Tyson Rendani
    The research project presented relates to the Mineral Resource evaluation of South Deep Gold Mine in Westonaria, South Africa. The aim of the project is to establish the impact of the inclusion of the samples from flatly inclined boreholes (FIBs) in the variography and Mineral Resource estimation of the individual Elsburg top conglomerate reef (ECT). The samples from FIB boreholes are traditionally excluded from the estimation process to reduce the possibility of smearing grade as stated in the Mine’s Code of Practice. These are boreholes with a dip of greater than -55° or less than 55o. These boreholes provide the highest resolution into the orebody and thus the highest level of de-risking of the orebody and are therefore used for geological modelling. Although the addition of the samples from FIBs in brings a substantial increase in the number of samples in some geostatistical domains they do not introduce outliers. Adding the FIBs resulted in improved variogram models. Simple Kriging models considered are one using the Au (g/t) samples from the steeply inclined holes only and the other using the combined dataset. These Kriging models were post-processed through Local Direct Conditioning (LDC) and the results were compared. Reconciliation indicates that the model remains stable with 1% change at Mineral Resource and Mineral Reserve cut-off of 3.2g/t Au following the addition of Au (g/t) samples from FIBs in the mineral resource estimation. It is therefore concluded that adding the flatly inclined boreholes in the mineral resource estimation increases the confidence in Kriging and improves variogram models
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    S-wave receiver function studies in African sedimentary basins
    (2017) Inguane, Helio Filemone
    Sedimentary basins are the result of prolonged subsidence of the Earth’s surface. They occupy 45% of the African surface. Knowledge of their area and depth is important because they often contain mineral, energy and groundwater resources. The transition between crust and mantle (the Moho) is believed to hold important clues to the Earth’s evolution and has been the subject of many studies, including P-wave Receiver Function (PRF) studies, to determine the structure and composition of the crust and uppermost mantle in Southern and Eastern Africa. The PRF method relies on the partial conversion of P-waves produced by teleseismic earthquakes to S-wave waves at the Moho. The travel-time delay between the direct P-wave and the Ps phase is used to deduce the thickness and average velocity of the crust. However, the PRF technique fails in regions where there is strong intracrustal layering (such as sedimentary basins), because the reverberations produced by the layers arrive at the seismometer simultaneously with the Ps phase. Here the S-wave Receiver Function (SRF) method works better, as the Sp phase arrives before any reverberations produced by intracrustal layering. In this study I have used the SRF method to investigate crustal structure beneath sedimentary basins in Southern and Eastern Africa. The aim of this research was to constrain the crustal thickness and shear wave velocity in seven sedimentary basins in Eastern and Southern Africa using S-wave Receiver Functions (SRFs). Teleseismic earthquakes with magnitude ≥5.5 and 60 to 82 degree epicentral distance were used to generate the SRFs using data acquired by seismic stations that were deployed between 2007 and 2013 in three rift basins (Lake Albert, Lake Edward and Rukwa) and four pull–apart basins (Mandawa, Mozambique, Rovuma and Ruvu). A moveout correction was made to align the SRFs obtained from different earthquakes, enabling them to be stacked to reduce random noise and enhance the signal-to-noise ratio of the SP phase and the accuracy of the pick of the SP arrival time. The SP arrival time uncertainties, typically 0.05 s of time error, were estimated for each station using the bootstrapping method. The surface wave group velocity models for each station (at 10, 15, 20, 25 and 30s periods) were used to constrain the depth–velocity models. The grid search modeling was performed using the DISPER80 package. The following crustal thicknesses (H) and average crustal shear velocities (Vs) were obtained:  Lake Albert and Lake Edward rift basins situated within the Mesoproterozoic Ruwenzori orogenic belt: H of 38.8 ± 2.4 km and 33.83 ± 0.9 km, respectively; Vs of 3.72 km/s and 3.73 km/s, respectively;  Rovuma, Mandawa and Ruvu pull–apart basins within the Neoproterozoic Mozambique mobile belt: H of 32.73 ± 1.8 km, 37.79 ± 2.2 km and 39.63 ± 2.2 km, respectively; Vs of 3.68 km/s, 3.76 km/s and 3.79 km/s, respectively; and  Phanerozoic Mozambique pull-apart basin: H of 36.9 ± 2.1 km and Vs of 3.7 km/s. These results were compared with previous studies. The crustal thickness reported in a global review of Proterozoic terrains (Durrheim and Mooney, 1994) ranged between 40-55 km, while Rudnick and Fountain (1995) reported an average thickness of 43 km. For stations located in basins in the Mesoproterozoic Ruwenzori orogenic belt, this study produced estimates of H and Vs of 36.3 ± 2.4 km and 3.7 km/s, respectively. Vs is similar to estimates by Julià et al. (2005) and Tugume et al. (2013) for stations in the same region, while H is a few kilometers thinner. This study obtained H of 32-40 km beneath Neoproterozoic pull-apart Tanzanian coastal basins located within the Mozambique mobile belt (Chatellier and Slevin, 1988), while Tugume et al. (2013) estimated the crust of the adjacent Tanzanian craton to be 39 km thick. In the Phanerozoic Mozambique basin, this study found H and Vs of 36.9 ± 2.1 km and 3.7 km/s, respectively. Kgaswane et al. (2009), using joint inversion of receiver functions and Rayleigh wave dispersion, estimated the H and Vs for the northeast Limpopo belt (west of the Mozambique basin) to be 40 ± 3 km and 3.7 km/s, respectively. In general, this study found thinner crust and slower Vs than previous studies. However, it is important to note that the station locations were different. Previous studies analysed P-wave Receiver Functions (PRFs) recorded by stations located in the interior of the continent and near to the Tanzania craton, while this study analysed S-wave Receiver Functions (SRFs) recorded by stations located in rift and coastal sedimentary basins. It is likely that the crust thinned during extension and continental break-up.
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