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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The response of marine finfish and invertebrates to seismic survey noise

Fewtrell, Jane Leah January 2003 (has links)
The oil and gas industry is of major economic importance to Australia. Offshore seismic surveys are an essential component of exploration for fossil fuel reserves. Offshore seismic surveys involve the use of arrays of air-guns that produce repetitive high energy, low frequency sound. There is increasing concern about the effect that the noise generated by a seismic survey has on the surrounding marine life. Various species of captive marine fish and one species of squid were exposed to the noise from a single Bolt PAR 600 B air-gun with a 20 cui firing chamber and a source level at 1 m of 203.6 dB re 1 μPa mean squared pressure. Ten trials were conducted in Jervoise Bay and two were carried out off the coast of Exmouth. A different noise regime was used in each trial, however most involved the use of approach-depart scenarios to simulate an actual seismic survey and a 10 second duty cycle. Noise levels received by the animals ranged between 128 - 192 dB re 1 μPa mean squared pressure. Behavioural observations of the fish and squid were made before, during and after air-gun noise exposure. The physiological stress response of the fish was monitored by measuring plasma cortisol and glucose levels before and after noise exposure. The sensory epithelium was removed from the ears of the fish prior to, immediately after and up to 86 days after air-gun noise exposure and examined using a scanning electron microscope. No statistically significant physiological stress response in fish was detected as a result of the air-gun noise exposure regimes used. Significant damage to the ciliary bundles of the sensory epithelium of the sacculus was observed in pink snapper (Pugrus auratus) that had been exposed to air-gun noise between 144 - 191 dB re 1 μPa for 1.71 hours. No regeneration of the hair bundles was observed 58 days after exposure to air-gun noise. / However, evidence of regeneration was observed between 58 and 86 days after noise exposure. Behavioural observations suggested that as air-gun noise levels increase, fish respond by swimming faster, in tighter groups and towards the bottom of the water column. Significant increases in alarm responses were observed in fish and squid to air-gun noise exceeding 158 - 163 dB re 1μPa. An increasing proportion of alarm responses were also observed as the noise level increased. A decrease in the frequency of alarm responses for repeated exposures was observed in squid and some fish. The implications of these findings are discussed with comparisons of noise levels measured from an actual 2678 cui seismic survey air-gun array.
2

Image resolution analysis: a new, robust approach to seismic survey design

Tzimeas, Constantinos 29 August 2005 (has links)
Seismic survey design methods often rely on qualitative measures to provide an optimal image of their objective target. Fold, ray tracing techniques counting ray hits on binned interfaces, and even advanced 3-D survey design methods that try to optimize o?set and azimuth coverage are prone to fail (especially in complex geological or structural settings) in their imaging predictions. The reason for the potential failure of these commonly used approaches derives from the fact that they do not take into account the ray geometry at the target points. Inverse theory results can provide quantitative and objective constraints on acquisition design. Beylkin??s contribution to this ?eld is an elegant and simple equation describing a reconstructed point scatterer given the source/receiver distribution used in the imaging experiment. Quantitative measures of spatial image resolution were developed to assess the e?cacy of competing acquisition geometries. Apart from the source/receiver con?guration, parameters such as the structure and seismic velocity also in?uence image resolution. Understanding their e?ect on image quality, allows us to better interpret the resolution results for the surveys under examination. A salt model was used to simulate imaging of target points located underneath and near the ?anks of the diapir. Three di?erent survey designs were examined. Results from these simulations show that contrary to simple models, near-o?sets do not always produce better resolved images than far-o?sets. However, consideration of decreasing signal-to-noise ratio revealed that images obtained from the far-o?set experiment are degrading faster than the near-o?set ones. The image analysis was performed on VSP ?eld data as well as synthetics generated by ?nite di?erence forward modeling. The predicted image resolution results were compared to measured resolution from the migrated sections of both the ?eld data and the synthetics. This comparison con?rms that image resolution analysis provides as good a resolution prediction as the prestack Kirchho? depth migrated section of the synthetic gathers. Even in the case of the migrated ?eld data, despite the presence of error introducing factors (di?erent signal-to-noise ratios, shape and frequency content of source wavelets, etc.), image resolution performed well exhibiting the same trends of resolution changes at di?erent test points.
3

Image resolution analysis: a new, robust approach to seismic survey design

Tzimeas, Constantinos 29 August 2005 (has links)
Seismic survey design methods often rely on qualitative measures to provide an optimal image of their objective target. Fold, ray tracing techniques counting ray hits on binned interfaces, and even advanced 3-D survey design methods that try to optimize o?set and azimuth coverage are prone to fail (especially in complex geological or structural settings) in their imaging predictions. The reason for the potential failure of these commonly used approaches derives from the fact that they do not take into account the ray geometry at the target points. Inverse theory results can provide quantitative and objective constraints on acquisition design. Beylkin??s contribution to this ?eld is an elegant and simple equation describing a reconstructed point scatterer given the source/receiver distribution used in the imaging experiment. Quantitative measures of spatial image resolution were developed to assess the e?cacy of competing acquisition geometries. Apart from the source/receiver con?guration, parameters such as the structure and seismic velocity also in?uence image resolution. Understanding their e?ect on image quality, allows us to better interpret the resolution results for the surveys under examination. A salt model was used to simulate imaging of target points located underneath and near the ?anks of the diapir. Three di?erent survey designs were examined. Results from these simulations show that contrary to simple models, near-o?sets do not always produce better resolved images than far-o?sets. However, consideration of decreasing signal-to-noise ratio revealed that images obtained from the far-o?set experiment are degrading faster than the near-o?set ones. The image analysis was performed on VSP ?eld data as well as synthetics generated by ?nite di?erence forward modeling. The predicted image resolution results were compared to measured resolution from the migrated sections of both the ?eld data and the synthetics. This comparison con?rms that image resolution analysis provides as good a resolution prediction as the prestack Kirchho? depth migrated section of the synthetic gathers. Even in the case of the migrated ?eld data, despite the presence of error introducing factors (di?erent signal-to-noise ratios, shape and frequency content of source wavelets, etc.), image resolution performed well exhibiting the same trends of resolution changes at di?erent test points.
4

Além da superfície: impactos do desenvolvimento na pesca artesanal de Regência Augusta - ES

Bicalho, Charlene Sales 29 May 2012 (has links)
Made available in DSpace on 2016-12-23T13:44:55Z (GMT). No. of bitstreams: 1 Charlene Sales Bicalho - Parte 1.pdf: 1117058 bytes, checksum: 9d5a45cc50f8a72cdea5b27e4166f95e (MD5) Previous issue date: 2012-05-29 / This study shows how the fishermen of Regency Augusta, district of Linhares-ES, ressignificam fishing and social practices in its work towards large-scale Projects (PGE s) deployed both the rio Doce and maritime space. Want to be investigated from the look of the fishermen as the process of transformation in practice against fishing impacts caused by these investments. The survey was carried out in the community, participating through qualitative methodology, in order to understand the dynamics of artisanal fishermen, their beliefs, Regencia Augusta, values, attitudes and habits. The analysis is based on two directions. On the one hand, the villagers reports and official environmental reports. On the other hand, the description of two meetings of the compensation plan of the Fishing Activity of 4 d Seismic Survey (PCAP), from the view of fishermen. The observation and analysis lead us to the following results: the modification of fishing areas held predominantly in rio to before the sea; insertion of new fishing methods; emergence of new occupations and forms of employment; restriction of fishing area because of seismic surveys carried out in the region for an oil company; conflicts among fishermen / Este estudo mostra como os pescadores artesanais de Regência Augusta, distrito de Linhares ES, ressignificam seus trabalhos pesqueiros e práticas sociais perante Projetos de Grande Escala (PGEs) implantados tanto o rio Doce quanto no espaço marítimo. Pretende-se investigar a partir do olhar dos pescadores como ocorre o processo de transformação na prática pesqueira frente aos impactos ocasionados por esses investimentos. A pesquisa participante foi realizada na comunidade, por meio de metodologia qualitativa, no intuito de compreender a dinâmica dos pescadores artesanais de Regência Augusta, suas crenças, valores, atitudes e hábitos. A análise baseia-se em duas direções. Por um lado, relatos dos moradores e relatórios ambientais oficiais. Por outro, a descrição de duas reuniões do Plano de Compensação da Atividade Pesqueira da Pesquisa Sísmica Marítima 4D (PCAP), a partir da visão dos pescadores. A observação e análise nos levam aos seguintes resultados: a alteração das áreas de pesca antes realizada predominantemente no rio para o mar; inserção de novas modalidades pesqueiras; surgimento de novas ocupações e formas de trabalho; restrição da área de pesca devido pesquisas sísmicas realizadas na região por uma empresa do setor petrolífero; conflitos entre pescadores
5

Hot Springs Inflow Controlled by the Damage Zone of a Major Normal Fault

Godwin, Steven Benjamin 01 April 2019 (has links)
Spring water inflow is distinct at Pah Tempe Hot Springs (also known as Dixie Hot Springs) situated within the damage zone of the Hurricane Fault in Timpoweap Canyon in Hurricane, Utah. Excising of the footwall by the Virgin River has created Timpoweap Canyon and allowed an unusual opportunity to study the spring inflow in relation to the fault damage zone. While correlation of these springs with the damage zone and visible fracture patterns on the canyon wall has been made, no subsurface faulting has been imaged to verify connection to these visible fractures and spring inflows (Nelson et al., 2009). The stream was logged and contoured to note the varying locations of spring water inflows in contrast with unsaturated Virgin River water. Seismic surveys were conducted and subsurface profiles made to locate offsets and faults. Photogrammetry was conducted and a three-dimensional model of the canyon and cliff wall was created to facilitate remote fracture mapping of this wallSubsurface features correlate to fractures, spring water inflow locations, and surface faults mapped by Biek (2002). This suggests that faulting and fracturing from the Hurricane Fault provides subsurface conduits for these thermal waters to rise. In one area in the stream, thermal inflow correlates with both subsurface offsets and major surface fractures. Numerous correlations between just spring water entry and subsurface offsets or surface fractures are also found. Fracture and fault density is atypical at Pah Tempe as these features do not diminish with distance from the main strand of the fault. This has led to the Sevier Orogeny accounting for creating the observed fracture conduits at Pah Tempe. Fractures in the canyon wall at Pah Tempe open west to east. This is indicative of the maximum horizontal compressive stress of southern Utah being north to south (Zoback and Zoback, 2015). Therefore the spring inflow at Pah Tempe is likely a result of the damage from the Hurricane Fault creating conduits for spring water to rise, rather than the Sevier Orogeny.
6

A Conceptual Model of Groundwater Flow at the Midway, Utah Fish Hatchery as Constrained by Geochemical, Physical Hydrogeological, and Geophysical Methods

Durrant, Camille 11 March 2005 (has links) (PDF)
In addition to a loss of potential revenues from Utah's $393 million sport fishing industry, the state expends millions of dollars every year on costs associated with whirling disease mitigation and prevention. A state fish hatchery at Midway, Utah was closed when the shallow unconfined aquifer being used for fish culture by spring discharge was deemed to be contaminated by whirling disease. An alternative water source may exist in a confined aquifer below this contaminated unconfined aquifer. However, the complex hydrostratigraphy presents a challenge in determining if this source is a viable resource for fish culture. Geological, physical, chemical, geophysical, and isotopic data were combined to create a conceptual model of the groundwater flow at the site and to determine the interactions this confined aquifer may have with the contaminated aquifer. This model divides groundwater at the hatchery into a shallow unconfined system, an upper confined system, and a lower confined system. The shallow unconfined system is characterized by a water table ~1m below ground surface, several active springs, fast travel times, modern water mixed with ancient hydrothermal water, relatively high TDS, and relatively enriched isotopic values. The confined aquifers have a smaller hydrothermal component, relatively depleted isotopic values, lower TDS, and modern recharge components. Two orthogonal shallow high-resolution seismic reflection profiles indicate substantial heterogeneity in the subsurface at the level of the confined systems at the hatchery. Several north-south trending normal discontinuities were interpreted as possible faults from the seismic profile oriented as a dip line, whereas the strike profile shows discontinuous layering without noticeable faulting. A well log profile for the site shows discontinuous tufa layers amid heterogeneous alluvium material. These tufa layers separate upward leaking confined aquifers from the unconfined system. It is only through the integration of several methods that such mixed systems, can be understood. In this study, the lower confined aquifer was found to be a sufficient and safe resource through the integration of numerous methods.
7

Využití a interpretace seismických povrchových vln v širokém oboru frekvencí / Application and interpretation of seismic surface waves in broad frequency range

Gaždová, Renata January 2012 (has links)
Submitted Ph.D. thesis is concerning the application and interpretation of seismic surface waves in a broad range of frequencies and scales. Using surface waves as a supplement to the methods dealing with body waves seems to be worth the effort. Surface wave interpretation can be used to obtain new information about the studied medium and simultaneously it can overcome, in some cases, the limitations of other seismic techniques. Moreover, surface waves are usually present on measured records and hence for its usage it is not necessary to modify the standard measuring procedures. One of the results of this thesis is an original algorithm for dispersive waveform calculation. The program works in an arbitrary range of frequencies and scales. The input parameter for the calculation is the dispersion curve. In this point the algorithm differs from all other approaches used so far. Algorithm is based on a summation of frequency components with shifts corresponding to the velocity dispersion and distance. The resulting waveform only contains an individual dispersive wave of the selected mode, thus being particularly suitable for testing of methodologies for dispersive wave analysis. The algorithm was implemented into the program DISECA. Furthermore, a new procedure was designed to calculate the dispersion...

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