A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, Johannesburg, September 2017 / Rockburst occurrences and their consequent damage remain a problem in modern mining, particularly at great depth. The problem of rockbursts has also escalated in deepcivilengineeringtunnelsduetohighlevelsofin-situstressatsuchdepths. Key advancementshavebeenmadetodatetohelpmitigatethedrasticimpactscausedby rockburstdamage,withrocksupportremainingalineofdefensetoprovidestability in rockbursting situations. There is, however, an ongoing inability of support to contain severe rockburst damage, especially conventional support systems. More than two decades ago, a support concept termed “sacrificial support” was proposed as a potential additional method to help inhibit rockburst damage. The philosophy behind a sacrificial support system is that, under dynamic loading conditions, support, in the form of a liner must fail (i.e. be ejected from rock surface), leaving behind, undamaged, what was once supported rock mass. It is because of this reason that this support is referred to as a sacrificial support due to its ability to protect the rock from damage whilst the support itself fails. Since the inception of this support idea, it was only recently that the behaviour of support in real rockburst events manifested the sacrificial behaviour in rockbursting, which warranted the need for further research. The sacrificial support concept stated here is applicable in situations where the source (i.e. seismic event) of the rockburst is located remote from where rockburst damage is likely to occur. To investigate the behaviour of sacrificial support, controlled laboratory experimentsbasedonthesplitHopkinsonpressurebar(SHPB)techniquewereconducted to study some aspects of dynamic rock fracturing in tension at high strain rates, and also the role a sacrificial layer plays in combating dynamic rock failure (i.e. rockburst damage). To achieve this, a single Hopkinson pressure bar configured for spalling tests, comprised of a relatively long cylindrical intact rock specimen attached at the bar free end, was impacted by a striker on the opposite free end of the bar in order to generate a dynamic stress pulse responsible for spall failure upon reflection from the specimen free end. Different liners and/or liner combinations were then introduced at the specimen free end as sacrificial support. This experimental arrangement allowed the role of, and failure mechanisms associated with, sacrificial support under dynamic loading to be demonstrated, and comparisons were made with “sacrificial support” behaviour observed in real rockburst events in a mine. Analysis of experimental results revealed that varying liner thickness and mechanical impedance between rock and support liner plays a significant role in helping to limit rockburst damage. Apart from experimental investigations, numerical simulations were undertaken to further probe the behaviour of sacrificial support under dynamic loading. Elastic models subjected to p-wave propagation indicated failure of the sacrificial layer, manifested by ejection of the liner due to reflection of compressive wave at the free surface. This failure mechanism was noticed for all the liners, independent of variation in liner thickness, and wavelength characteristic of the applied wave to the model. The sacrificial support method presented in this thesis presents an opportunity to further enhance safety in seismically active mines. / XL2018

Thesis (Ph.D.)--University of the Witwatersrand, Science Faculty (Geophysics), 1980 / The physical processes at the source of mine tremors at the East Rand Proprietary Mines (E.R.P.M.) near Johannesburg were investigated. [Abbreviated Abstract. Open document to view full version] / AC2017

Several seismic precursors and earthquake-causing variables have been proposed in the last decades based on physical considerations and case observations, however none has been confirmed on long datasets using linear analysis. This work adopts an information-theoretical approach to investigate the occurrence of causal flow between these precursors and causing variables and seismicity. It starts by introducing the key concepts in seismology and presenting the current main precursor candidates. Four variables will be considered as possible precursors or anomalies leading to earthquakes: large tidal amplitudes, temporal fluctuations in the Gutenberg-Richter's b-value, surface gravity changes, and preceding anomalous seismicity patterns. To perform the causality test between these variables and their effects, it is developed a method which allows the fast calculation of Transfer Entropy for any two time-series, detecting the direction of the flow of information between the variables of interest. The method is tested to coupled logistic maps and networks with different topologies before application to geophysical events. The analysis shows mutual information relating to coupling strength and also allows inference of the causal direction from data using the Transfer Entropy, both in bivariate systems and in networks. The method was then applied to the earthquake analysis for an interval of 4018 days on an area comprising the Japan trench. Within a conservative margin of confidence, the results could not at this point confirm any of the four precursor options considered, but future work can clarify initial suggestions regarding tidal amplitudes link to seismicity, and pre-seismic gravity changes and cumulative daily magnitude anomalies. The Matlab/Octavecodes for our method are open-source and available at https://github.com/artvalencio/causality-toolbox We hope the method is able to support the quest for other precursor candidates, and to assist other fields of knowledge.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb. 12, 2010 ). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dr. Francisco Gomez, Thesis Supervisor. Includes bibliographical references.

Whether by accretion, magmatic addition, or refinement of more mafic lithologies, continental arcs are likely zones for the creation of "average" continental crust with intermediate silica content. This dissertation contains the results of broadband seismic studies carried out in two field areas, an active subduction zone and the remnants of an extinct arc, with the aim of understanding lithospheric evolution at convergent margins. The analytical techniques of receiver function calculation and surface wave tomography are applied to data sets collected above the Andean subduction zone in Chile and western Argentina and in the Coast Mountains Batholith of central British Columbia. We present the first in-depth comparison of receiver functions calculated using the high frequencies available in records of intermediate-depth local earthquakes with those calculated from the lower frequency data in records of larger teleseismic events. The comparison reveals that the lower crust beneath the Western Sierras Pampeanas contains a gradational velocity increase over ~20km above a small velocity step at the Moho. Surface wave tomography confirms the existence of an unusually high velocity anomaly in the mantle above the slab and yields estimates of slab thickness on the order of 50 km. To the south of the flat slab region, we see evidence of active mantle wedge convection above the steep slab, but no evidence of the lithosphere-asthenosphere boundary beneath the subducting Nazca plate. In the Coast Mountains Batholith (CMB), receiver functions image a bright, continuous Moho throughout the study region. Combined with petrologic modeling, the receiver function data point toward convective removal of any ultramafic root that formed beneath the CMB. Low absolute shear wave velocities in the upper mantle resolved via surface wave analysis strengthen the case for root removal beneath the eastern section of the CMB. On the far western edge of the CMB, we find evidence of a partially reformed lithosphere outboard of a major tectonic boundary. These observations shed light on the distillation of felsic to intermediate continental crust from more mafic primary magmas in active subduction zones and the eventual return of the complementary ultramafic residuals to the convecting mantle.

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