A project report submitted to the Faculty of Mining Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. / A strategy to determine the probability that a mining induced seismic event will occur with magnitude which exceeds some specified value within a given time is investigated. The model allows for a non-linear frequency-magnitude relationship and a Poissonian distribution of seismic events in time. The procedure is also independent of the method of mining and of the mining geometry. The model was applied to clusters of various sizes) starting from small areas on a single reef and ending up with the entire mine as a single entity. It was shown that the model works well with large populations of events, but to be successful with small clusters, the retention of the Poisson distribution is too restrictive and a non-stationary model of seismicevent occurrence in time will have to be developed. / AC 2018

This dissertation presents an analysis of the spatiotemporal variations of strong ground shaking and style of faulting at regional scales in the Chilean subduction zone. These properties are part of the two main components of seismic hazard: ground motions and seismic source characterization. Results are interpreted to be related to the tectonic dynamics and heterogeneities in the region. The ground motion component was evaluated using residual analysis between observed and predicted earthquake strong ground motions. By analyzing strong motions of interplate earthquakes along the Chilean subduction zone (from the northern border to the tectonic triple junction in the south), we corroborate the better predictive performance of locally-derived ground motion models over globally-derived models. The results presented here show a stronger short-period radiation generated by deeper interplate earthquakes in north and central Chile, which is not currently considered in local ground motion models. We interpret this depth-dependent radiation pattern as a result of frictional variations on the plate interface. Additionally, it is shown that not every aftershock sequence following a large interplate earthquake exhibits predominantly weaker short-period radiation, which could be dependent on whether there was precursory activity before the mainshock. This work also outlines the need of developing local ground motion models for crustal earthquakes, since ground motion observations from the Mw 5.7 Pica earthquake (a crustal reverse-oblique event in northern Chile with a large stress drop) are significantly larger than predictions from current global models, particularly at short periods. The seismic source component was assessed for crustal earthquakes in northern Chile. Clear regionalization is found in the spatial patterns of style of faulting and the tectonic stress field. The coastal region exhibits a clear margin-parallel compressional regime shown by the mostly reverse and strike-slip earthquakes in this area, while the analyzed portion of the Andean Precordillera shows a strike-slip regime with a compressional direction nearly parallel to the plate convergence direction. We interpret these two tectonic regimes as a result of the concave shape of the subduction margin and the effect of local topography, respectively. Our results show that these regimes do not show any temporal change during the ∼10 year analysis period, and likely have remained stationary for the last 10 Ma. Although the earthquake recurrence relations presented in this work show that crustal earthquakes happen less frequently and at smaller magnitudes than interplate and intraplate earthquakes in northern Chile, crustal earthquakes still pose an important hazard, with the possibility of occurrence of more earthquakes with damaging-level ground accelerations, such as the Pica earthquake. / Graduate

Situated in the Bengal Basin, the Ganges-Brahmaputra river delta comprises one of the largest fluviodeltaic systems in the world, comprising ∼ 100,000 km2 of floodplain and delta plain and a 40,000 km2 subaqueous delta on the shelf. Sediment load of the Ganges-Brahmaputra river is 109 t/yr, and seasonal flooding may inundate >70% of the delta during large events. Active tectonic processes have resulted in both uplift and subsidence in this structurally complex region. These general characteristics suggest that the Ganges-Brahmaputra delta represents a heretofore undescribed delta end-member, forming along a high-yield, high-energy, tectonically active margin. to investigate this view, stratigraphic, sedimentologic, and geochronologic data are used to evaluate processes, controls, and development of the system over different spatial and temporal scales in the Late Quaternary.;Results of a century-scale sediment accretion study using radioisotope geochronology indicate that ∼ 30% of fluvial sediment load is sequestered to the delta and not reaching the coastal ocean as previously assumed. A Holocene-scale sediment budget generated from radiocarbon-dated stratigraphy also reveals ∼ 30% of sediment discharge was sequestered to the delta during this time. Considered with offshore data, these sediment budgets indicate contemporaneous highstand strata formation across floodplain, shelf, and deep-sea depocenters. Radiocarbon-dated stratigraphy was used to reconstruct the Late Quaternary history of delta formation. Growth of the Ganges-Brahmaputra delta began ∼ 10,000--11,000 cal yr BP, notably 2000--3000 years prior to most of the world's deltas. During subsequent rapid sea-level rise, the immense sediment discharge was sufficient to maintain relative shoreline stability while most margin systems experienced major transgression. offset of radiocarbon dates from eustatic sea level indicate 2--4 mm/yr of subsidence in several areas of the delta, suggesting tectonic control on deltaic sediment trapping and sequence formation. Shallow vibracore stratigraphy from the delta reveals a cap of muddy sediments overlying largely sandy material, reflecting differences in preservation between floodplain and channel deposits. Over longer time frames, floodplain sediments are eroded through channel migration and avulsion, thus preferentially preserving channel sands. Overall, the role of tectonics in controlling deltaic processes and product in the Ganges-Brahmaputra river delta implies a fundamental distinction for deltas forming along active margins.

A two-year period of monthly slack water survey results suggest that in addition to the classical estuary turbidity maximum (ETM), a second peak of bottom total suspended sediments (TSS) concentration, or a secondary turbidity maximum (STM), often exists in the mid-York Estuary. This STM, detected from majority of the slack water surveys, moves back and forth in the region of about 20--40 km from the York River mouth. Moreover, the distribution of potential energy anomaly indicates that the STM may be related to the stratification patterns of the water column. A mathematical analysis suggests that four processes may be important to the formation of the STM: convergence of bottom residual flow, tidal asymmetry, inhibition of turbulence diffusion by stratification, and local erosion. An intensive survey was conducted in the middle part of the York River. None of the four mechanisms was in favor of convergent sediment transport in the examined region. Accordingly, the STM did not show up in the slack water survey conducted two days before the intensive survey. The intra-tidal variations of the bottom TSS concentration was shown to be proportional to bottom shear stress in most stations, which indicates that bottom resuspension is an important source of TSS in this region. The survey results also suggest that lateral sediment transport is not negligible in the study area. A three-dimensional numerical model was applied to the York River system. The model reproduced the basic features in both the salinity and TSS fields. Sensitivity model studies confirmed the existence of the STM under low and mean flow conditions. Analysis to the model results shows that bottom resuspension is an important source of TSS in both the ETM and the STM. The location of the ETM is well associated with the null point of bottom residual flow under various flow conditions. Convergent bottom residual flow, as well as tidal asymmetry, were shown to be the most important mechanisms that contribute to the formation of the STM. Model results suggest that the association between the STM and the stratification pattern is due to geometric features.

A 3D velocity model and 3D wave propagation code have been employed to simulate long-period ground motions in the upper Mississippi embayment. This region is exposed to seismic hazard in the form of large earthquakes in the New Madrid seismic zone and observational data are sparse, making simulation a valuable tool for predicting the effects of large events. These simulations were undertaken in order to estimate ground-motion characteristics and to investigate the influence of the 3D embayment structure and finite-fault mechanics. There are three primary fault zones in the New Madrid seismic zone, each of which was likely associated with one of the three main shocks of the 1811-1812 earthquake sequence. For this study, three simulations have been conducted on each major segment, evaluating the effects of different epicentral locations and rupture directions on ground motions. The full wave field up to a frequency of 0.5 Hz was computed on a 200 × 200 × 50 km3 volume, and up to a frequency of 1.0 Hz on a 100 × 100 × 50 km3 volume, using a staggered-grid finitedifference code. Peak horizontal velocity, bracketed durations, and pseudospectral accelerations were calculated at the free surface. Animations showing the evolution of peak horizontal velocity through time at the free surface were also generated. The New Madrid seismic zone simulations indicate that for the considered bandwidth, finite-fault mechanics such as fault proximity, directivity effect, and slip distribution exert the most control on ground motions. The 3D geologic structure of the upper Mississippi embayment also influences ground motion, with indications that the bedrock surface acts as a wave guide, trapping waves in shallow, low-velocity parts of the embayment.

An Enhanced Geothermal System (EGS) allows for the generation of electricity using the Earth's heat by improving ('enhancing') the fracture permeability of rock and flowing fluid through the optimized medium. The complex behavior of EGS fracture systems and heat flow processes are being studied at various scales to determine the practical capabilities of EGS technology. The EGS collaborative (Collab) project is focused on experimentation of intermediate-scale (i.e., 10's of meters) EGS reservoir generation processes and model validation at crystalline rock sites. A key phase of the project involves seismic characterization of a rock mass intended to be representative of EGS reservoir rock. A suite of boreholes was drilled from inside a mine drift on the 4850-foot (~1.5 km) level of the Sanford Underground Research Facility (SURF) in Lead, South Dakota. The boreholes, comprised of one stimulation (injection) well, one production (extraction) well, and six monitoring wells, were each nominally drilled approximately 200 feet (~60 meters) deep into the surrounding crystalline rock formation near the location of a previous experiment at this site (kISMET). Active source seismic data were collected using an electrical sparker source and an electro-mechanical impulse source to generate compressional (P-) wave and shear (S-) wave energy, respectively, at varying depths in the stimulation well. Seismic receivers were deployed in the sub-parallel production well, in addition to receivers installed in the monitoring wells, to detect P- and S-wave arrivals. Over the summer, I picked all the P-wave arrivals and helped generate initial tomographic models. The 3D P- and S-wave velocity models associated with these are presented here with a discussion of the elastic parameters they imply. The rock is found to be more complicated and heterogeneous than expected. Velocity and calculated elastic moduli values are reasonable for crystalline rock. These elastic parameters are used for modeling and monitoring seismic hypocenters that are associated with fracture propagation during EGS stimulation activities.

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Thesis (Ph. D.). UM #9842342. / Title from document title page. Includes bibliographical references. Available in PDF format via the World Wide Web.