Using ambient noise tomography to image the Eastern Cape-Karoo and Karoo regions, South Africa
- Bezuidenhout, Lucian John-Ross
- Authors: Bezuidenhout, Lucian John-Ross
- Date: 2018
- Subjects: Geometric tomography -- South Africa , Geobiology Geology -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23602 , vital:30585
- Description: The primary aim of this thesis was to explore the use of ambient seismic noise as a tool to map the subsurface of the Cape-Karoo and Karoo region of South Africa. The Karoo is an ideal laboratory to use ambient seismic signal to map the shallow subsurface, as it is a quiet and pristine environment with a relatively well known geology. Ambient seismic signals were continuously recorded at three independent networks (ArrayA, ArrayB and ArrayC). ArrayA and ArrayB comprised 17 temporary stand-alone seismic stations each and recorded ambient noise wavefields for a ten week period between August and October 2015. ArrayC comprised 19 temporary stand-alone seismic stations, recording ambient seismic noise for a period of six weeks between June and July 2016. ArrayA and ArrayB were installed in the south-eastern Cape-Karoo region, near the town of Jansenville and ArrayC was installed near the Cradock-Tarkastad region of South Africa. This thesis is made up of two separate studies. Firstly, the retrieval and coherency of Rayleigh surface waves extracted from the vertical component recordings. For the first time in the south-eastern Cape-Karoo and Karoo area, estimates of Green’s function from cross-correlating ambient noise data between stations pairs were reconstructed and shown, which can be successfully used to image the subsurface. The stacked cross-correlations between all station pairs show clear arrivals of the Rayleigh surface waves. The group velocities of the Rayleigh waves in the 2 to 7 seconds period range were picked and inverted to compute the 2-D group velocity maps. For ArrayA and ArrayB, the resulting 2-D group velocity maps at different periods resulted in a group velocity model from approximately 2 to 7 km depth, which generally show a high velocity anomaly in the north of the study area, most likely imaging the denser, thick sedimentary basin of the Karoo (Carboniferous-Permian). To the south, the low velocity anomaly likely corresponds to the overlying Jurassic- Cretaceous sequences of the younger Algoa Basin (Uitenhage Group). For ArrayC, the group velocity maps showed high velocity regions, which is consistent with the dolerite sill intrusions in the Karoo and the low velocity structures, which was interpreted as the Karoo sediments. Secondly, the study comprised of characterizing the ambient seismic noise source. The first order analysis of the symmetry of the cross-correlation function showed that, although the ambient noise sources are relatively homogeneously distributed in the study area, most (energetic) of the ambient seismic noise propagates from the coast of South Africa. This was verified by analyzing the azimuthal distribution of the ambient seismic noise.
- Full Text:
- Date Issued: 2018
- Authors: Bezuidenhout, Lucian John-Ross
- Date: 2018
- Subjects: Geometric tomography -- South Africa , Geobiology Geology -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23602 , vital:30585
- Description: The primary aim of this thesis was to explore the use of ambient seismic noise as a tool to map the subsurface of the Cape-Karoo and Karoo region of South Africa. The Karoo is an ideal laboratory to use ambient seismic signal to map the shallow subsurface, as it is a quiet and pristine environment with a relatively well known geology. Ambient seismic signals were continuously recorded at three independent networks (ArrayA, ArrayB and ArrayC). ArrayA and ArrayB comprised 17 temporary stand-alone seismic stations each and recorded ambient noise wavefields for a ten week period between August and October 2015. ArrayC comprised 19 temporary stand-alone seismic stations, recording ambient seismic noise for a period of six weeks between June and July 2016. ArrayA and ArrayB were installed in the south-eastern Cape-Karoo region, near the town of Jansenville and ArrayC was installed near the Cradock-Tarkastad region of South Africa. This thesis is made up of two separate studies. Firstly, the retrieval and coherency of Rayleigh surface waves extracted from the vertical component recordings. For the first time in the south-eastern Cape-Karoo and Karoo area, estimates of Green’s function from cross-correlating ambient noise data between stations pairs were reconstructed and shown, which can be successfully used to image the subsurface. The stacked cross-correlations between all station pairs show clear arrivals of the Rayleigh surface waves. The group velocities of the Rayleigh waves in the 2 to 7 seconds period range were picked and inverted to compute the 2-D group velocity maps. For ArrayA and ArrayB, the resulting 2-D group velocity maps at different periods resulted in a group velocity model from approximately 2 to 7 km depth, which generally show a high velocity anomaly in the north of the study area, most likely imaging the denser, thick sedimentary basin of the Karoo (Carboniferous-Permian). To the south, the low velocity anomaly likely corresponds to the overlying Jurassic- Cretaceous sequences of the younger Algoa Basin (Uitenhage Group). For ArrayC, the group velocity maps showed high velocity regions, which is consistent with the dolerite sill intrusions in the Karoo and the low velocity structures, which was interpreted as the Karoo sediments. Secondly, the study comprised of characterizing the ambient seismic noise source. The first order analysis of the symmetry of the cross-correlation function showed that, although the ambient noise sources are relatively homogeneously distributed in the study area, most (energetic) of the ambient seismic noise propagates from the coast of South Africa. This was verified by analyzing the azimuthal distribution of the ambient seismic noise.
- Full Text:
- Date Issued: 2018
Understanding suicide: a psychobiographical study of Ian Kevin Curtis
- Authors: Kitching, Philip Herman
- Date: 2017
- Subjects: Psychology -- Biographical methods Personality -- Research -- Methodology , Suicide Suicidal behavior
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/18178 , vital:28583
- Description: Psychobiography can be viewed as the re-writing of an individual‟s life story previously undetected. In general, it consists of a combination of two central elements: biography and psychological theory, which aim to explain the particular individual‟s psychological development. This particular study serves to explore the extraordinary life of renowned singer and songwriter, Ian Kevin Curtis (1956-1980), who died by suicide at the early age of 23. The basis for this investigation will take the form of notable biographical accounts of the subject‟s life, together with the application of Thomas Joiner‟s (2005) interpersonal-psychological theory of suicide which identifies factors that lead to suicidal ideation - in an attempt to understand the psychological circumstances that contributed to Curtis‟s suicide. In doing so, Adler‟s (1929) theory of Individual Psychology was applied to the life of Curtis in an attempt to build on Joiner‟s theory. This led to the concept of control being introduced and contributed to the development of an intake form to identify those at risk for suicide. It is hoped that exploring the psychological circumstances that contributed to Curtis‟s suicide and their interpretation by the subject will bring about an understanding of the risk factors that may induce suicide and, by extension, will highlight the relevance of this psychobiographical study as a tool for investigating and promoting preventative measures concerning suicide. The psychobiographical data collection and analysis for this research thesis will be guided by Yin‟s (2003) theory of „analytic generalisation‟ which uses a theoretical framework in selecting relevant data which develops a matrix as a descriptive framework for organising and integrating that data, and Alexander‟s (1988) analytical model which focuses on lifting out themes through principal identifiers of salience.
- Full Text:
- Date Issued: 2017
- Authors: Kitching, Philip Herman
- Date: 2017
- Subjects: Psychology -- Biographical methods Personality -- Research -- Methodology , Suicide Suicidal behavior
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/18178 , vital:28583
- Description: Psychobiography can be viewed as the re-writing of an individual‟s life story previously undetected. In general, it consists of a combination of two central elements: biography and psychological theory, which aim to explain the particular individual‟s psychological development. This particular study serves to explore the extraordinary life of renowned singer and songwriter, Ian Kevin Curtis (1956-1980), who died by suicide at the early age of 23. The basis for this investigation will take the form of notable biographical accounts of the subject‟s life, together with the application of Thomas Joiner‟s (2005) interpersonal-psychological theory of suicide which identifies factors that lead to suicidal ideation - in an attempt to understand the psychological circumstances that contributed to Curtis‟s suicide. In doing so, Adler‟s (1929) theory of Individual Psychology was applied to the life of Curtis in an attempt to build on Joiner‟s theory. This led to the concept of control being introduced and contributed to the development of an intake form to identify those at risk for suicide. It is hoped that exploring the psychological circumstances that contributed to Curtis‟s suicide and their interpretation by the subject will bring about an understanding of the risk factors that may induce suicide and, by extension, will highlight the relevance of this psychobiographical study as a tool for investigating and promoting preventative measures concerning suicide. The psychobiographical data collection and analysis for this research thesis will be guided by Yin‟s (2003) theory of „analytic generalisation‟ which uses a theoretical framework in selecting relevant data which develops a matrix as a descriptive framework for organising and integrating that data, and Alexander‟s (1988) analytical model which focuses on lifting out themes through principal identifiers of salience.
- Full Text:
- Date Issued: 2017
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