Através de perfis sísmicos de alta resolução (3,5 kHz), coletados entre os anos de 2009 e 2014, foi possível analisar o fundo e sub-fundo marinho da plataforma continental interna do Rio Grande Sul, mais especificamente em frente à desembocadura do estuário da Lagoa dos Patos. Estes dados permitiram observar anomalias acústicas caracterizadas como sendo uma resposta à presença de gás intersticial no sedimento. As acumulações foram identificadas com base na morfologia, dimensão, tipo de assinatura acústica e concentração aparente de gás. Assim, cinco formas distintas de gás raso foram reconhecidas: cortina de gás, blanking acústico, turbidez acústica, pináculo de turbidez e pluma intra-sedimentar. Tais estruturações se apresentaram isoladas ou então relacionadas umas com as outras. Dentre estas, as cortinas de gás e blanking acústico foram as que ocorreram em maior número e área. As cortinas apresentaram morfologia bem definida, em formato de caixa, onde o gás se encontra mais concentrado. O blanking acústico, formado pela presença de bolhas de gás bem disseminadas no sedimento, foi distinguido por uma forte reflexão de topo e um mascaramento dos refletores subjacentes, sem demonstrar limites laterais bem definidos A turbidez acústica, associada à disseminação de gás moderada a alta, é uma perturbação de sinal pela presença de bolhas no sedimento em quantidades que apenas atenuam a energia sísmica, possibilitando identificar algum refletor abaixo do seu topo. Os pináculos de turbidez encontrados são pequenos e apresentaram forma pontiaguda, indicando uma disseminação de gás baixa a moderada. A pluma intra-sedimentar encontrada apresentou formato quase parabólico, interpassando a camada de sedimentos de modo que o gás presente nela é baixo a moderadamente disseminado. Tais formas estão diretamente ligadas com a distribuição das fácies sedimentares, as quais agem como reservatório e selante, retendo ou não o gás e gerando as diferentes respostas acústicas. A ocorrência do gás está concentrada em frente à desembocadura da Lagoa dos Patos, local de deposição de sedimentos finos e matéria orgânica. Este aporte lagunar e o retrabalhamento da plataforma por eventos de regressão e transgressão marinha no Quaternário permitiram a gênese e preservação do gás em sedimentos holocênicos, de provável origem biogênica. / Using high-resolution (3.5 kHz) seismic profiles collected between 2009 and 2014, it was possible to analyze the bottom and sub-bottom geoacoustics characteristics of the inner continental shelf of the Rio Grande Sul, more specifically in front of the mouth of the estuary of the Patos Lagoon. The data allowed observing acoustic anomalies characterized like being a response to gas presence in the sediment. The gas accumulations were identified based on their morphology, dimension, type of acoustic signature and apparent concentration of gas. Thus, five different features of shallow gas were recognized: gas curtain, acoustic blanking, acoustic turbidity zone, turbidity pinnacle and intra-sedimentary plume. These structures have been isolated or then related each other. Among these, the gas curtain and acoustic blanking were those that occurred in greater number and area. Gas curtains presented well defined morphology, in gas boxes format, where the gas is more concentrated. Acoustic blacking, originated from presence of well disseminated gas bubbles in the sediment, was distinguished by a strong top reflection that masks the below reflectors, without to show well defined lateral limits Acoustic turbidity zone, associated with the dissemination of moderate to high gas, is a signal disturbance due to the presence of bubbles in the sediment in quantities that only attenuate the seismic energy, allowing yet identifying some reflector below its top. Turbidity pinnacles found are small and present pointed shape, indicating to a low to moderated gas dissemination. Intra-sedimentary plume found presented an almost parabolic shape, penetrating across the sediment layer thus the gas dissemination in the plume is low to moderate. These forms are linked directly with the sedimentary facies distribution, which act like reservoir and sealant, retaining or not the gas and producing the distinct acoustic response. The gas is concentrated in front of the mouth of Patos Lagoon, deposition site of fine sediments and organic matter. Such lagoon sediment input and the reworking of the shelf by marine regression and transgression events during Quaternary allowed the genesis and preservation of gas occurring in the Holocene sediments, which origin is probable biogenic.

The purpose of this master thesis is to evaluate the results from the completed SCPT (Seismic Cone Penetration Test) surveys with respect to the methods ability to estimate dynamic young´s modulus. This has been done by comparing the result from SCPT to other seismic methods and dynamic parameters converted from “static” geotechnical surveys. SCPT is a relatively new method which has not been used by Sweco or in Sweden to any greater extent and is therefore of interest to be looked in to. By adding two geophones to an ordinary CPT (Cone Penetration Test) equipment as well as including strike plates, hammer and logger system one can log dynamic parameters in addition to the regular parameters logged by a CPT system. This is done by stopping the otherwise continuous CPT survey every meter and striking the strike plates, which are placed under the tracks of the drilling rig. Seismic waves will then travel through the soil down to the geophones and be used to calculate dynamic parameters. For this master thesis a total of 47 geotechnical and geophysical surveys have been considered. The location of these 47 are approximately 7 km north of Norrköping and have been conducted between the years 2016-2017 for the East Link Project. The geotechnical surveys are composed of weight-sounding, ram-sounding and CPT while the geophysical ones are SCPT, refraction-survey and MASW (Multichannel Analysis of Surface Waves). Static elastic parameters have been calculated using the geotechnical survey results according to the Swedish transportation administrations standardized methods. These have then been converted to dynamic parameters with the help of different relationships. When these have been converted they can be compared to SCPT results and other seismic survey methods which also use wave velocity, Poisson’s ratio and density to calculate dynamic elastic parameters. Based on the results from this thesis it can be concluded that the seismic test add-on to a standard CPTu survey is a good method for accessing dynamic modules and it gives extended information of the soil stratigraphy from one single survey point. After the studies and analyses conducted for this thesis it can be concluded that the proposed conversion between static and dynamic young’s modulus using the Alpan curve gives slightly higher values than the ones derived directly from shear waves using SCPT. The other conversion using cone tip resistance to shear wave velocity gives on the other hand slightly lower values than the ones measured with the SCPT. The analysis also indicate similar trends in results between the different seismic methods. These results does however also shows that the used assumptions are somewhat general for accurate comparisons between the methods.

Através de perfis sísmicos de alta resolução (3,5 kHz), coletados entre os anos de 2009 e 2014, foi possível analisar o fundo e sub-fundo marinho da plataforma continental interna do Rio Grande Sul, mais especificamente em frente à desembocadura do estuário da Lagoa dos Patos. Estes dados permitiram observar anomalias acústicas caracterizadas como sendo uma resposta à presença de gás intersticial no sedimento. As acumulações foram identificadas com base na morfologia, dimensão, tipo de assinatura acústica e concentração aparente de gás. Assim, cinco formas distintas de gás raso foram reconhecidas: cortina de gás, blanking acústico, turbidez acústica, pináculo de turbidez e pluma intra-sedimentar. Tais estruturações se apresentaram isoladas ou então relacionadas umas com as outras. Dentre estas, as cortinas de gás e blanking acústico foram as que ocorreram em maior número e área. As cortinas apresentaram morfologia bem definida, em formato de caixa, onde o gás se encontra mais concentrado. O blanking acústico, formado pela presença de bolhas de gás bem disseminadas no sedimento, foi distinguido por uma forte reflexão de topo e um mascaramento dos refletores subjacentes, sem demonstrar limites laterais bem definidos A turbidez acústica, associada à disseminação de gás moderada a alta, é uma perturbação de sinal pela presença de bolhas no sedimento em quantidades que apenas atenuam a energia sísmica, possibilitando identificar algum refletor abaixo do seu topo. Os pináculos de turbidez encontrados são pequenos e apresentaram forma pontiaguda, indicando uma disseminação de gás baixa a moderada. A pluma intra-sedimentar encontrada apresentou formato quase parabólico, interpassando a camada de sedimentos de modo que o gás presente nela é baixo a moderadamente disseminado. Tais formas estão diretamente ligadas com a distribuição das fácies sedimentares, as quais agem como reservatório e selante, retendo ou não o gás e gerando as diferentes respostas acústicas. A ocorrência do gás está concentrada em frente à desembocadura da Lagoa dos Patos, local de deposição de sedimentos finos e matéria orgânica. Este aporte lagunar e o retrabalhamento da plataforma por eventos de regressão e transgressão marinha no Quaternário permitiram a gênese e preservação do gás em sedimentos holocênicos, de provável origem biogênica. / Using high-resolution (3.5 kHz) seismic profiles collected between 2009 and 2014, it was possible to analyze the bottom and sub-bottom geoacoustics characteristics of the inner continental shelf of the Rio Grande Sul, more specifically in front of the mouth of the estuary of the Patos Lagoon. The data allowed observing acoustic anomalies characterized like being a response to gas presence in the sediment. The gas accumulations were identified based on their morphology, dimension, type of acoustic signature and apparent concentration of gas. Thus, five different features of shallow gas were recognized: gas curtain, acoustic blanking, acoustic turbidity zone, turbidity pinnacle and intra-sedimentary plume. These structures have been isolated or then related each other. Among these, the gas curtain and acoustic blanking were those that occurred in greater number and area. Gas curtains presented well defined morphology, in gas boxes format, where the gas is more concentrated. Acoustic blacking, originated from presence of well disseminated gas bubbles in the sediment, was distinguished by a strong top reflection that masks the below reflectors, without to show well defined lateral limits Acoustic turbidity zone, associated with the dissemination of moderate to high gas, is a signal disturbance due to the presence of bubbles in the sediment in quantities that only attenuate the seismic energy, allowing yet identifying some reflector below its top. Turbidity pinnacles found are small and present pointed shape, indicating to a low to moderated gas dissemination. Intra-sedimentary plume found presented an almost parabolic shape, penetrating across the sediment layer thus the gas dissemination in the plume is low to moderate. These forms are linked directly with the sedimentary facies distribution, which act like reservoir and sealant, retaining or not the gas and producing the distinct acoustic response. The gas is concentrated in front of the mouth of Patos Lagoon, deposition site of fine sediments and organic matter. Such lagoon sediment input and the reworking of the shelf by marine regression and transgression events during Quaternary allowed the genesis and preservation of gas occurring in the Holocene sediments, which origin is probable biogenic.

Através de perfis sísmicos de alta resolução (3,5 kHz), coletados entre os anos de 2009 e 2014, foi possível analisar o fundo e sub-fundo marinho da plataforma continental interna do Rio Grande Sul, mais especificamente em frente à desembocadura do estuário da Lagoa dos Patos. Estes dados permitiram observar anomalias acústicas caracterizadas como sendo uma resposta à presença de gás intersticial no sedimento. As acumulações foram identificadas com base na morfologia, dimensão, tipo de assinatura acústica e concentração aparente de gás. Assim, cinco formas distintas de gás raso foram reconhecidas: cortina de gás, blanking acústico, turbidez acústica, pináculo de turbidez e pluma intra-sedimentar. Tais estruturações se apresentaram isoladas ou então relacionadas umas com as outras. Dentre estas, as cortinas de gás e blanking acústico foram as que ocorreram em maior número e área. As cortinas apresentaram morfologia bem definida, em formato de caixa, onde o gás se encontra mais concentrado. O blanking acústico, formado pela presença de bolhas de gás bem disseminadas no sedimento, foi distinguido por uma forte reflexão de topo e um mascaramento dos refletores subjacentes, sem demonstrar limites laterais bem definidos A turbidez acústica, associada à disseminação de gás moderada a alta, é uma perturbação de sinal pela presença de bolhas no sedimento em quantidades que apenas atenuam a energia sísmica, possibilitando identificar algum refletor abaixo do seu topo. Os pináculos de turbidez encontrados são pequenos e apresentaram forma pontiaguda, indicando uma disseminação de gás baixa a moderada. A pluma intra-sedimentar encontrada apresentou formato quase parabólico, interpassando a camada de sedimentos de modo que o gás presente nela é baixo a moderadamente disseminado. Tais formas estão diretamente ligadas com a distribuição das fácies sedimentares, as quais agem como reservatório e selante, retendo ou não o gás e gerando as diferentes respostas acústicas. A ocorrência do gás está concentrada em frente à desembocadura da Lagoa dos Patos, local de deposição de sedimentos finos e matéria orgânica. Este aporte lagunar e o retrabalhamento da plataforma por eventos de regressão e transgressão marinha no Quaternário permitiram a gênese e preservação do gás em sedimentos holocênicos, de provável origem biogênica. / Using high-resolution (3.5 kHz) seismic profiles collected between 2009 and 2014, it was possible to analyze the bottom and sub-bottom geoacoustics characteristics of the inner continental shelf of the Rio Grande Sul, more specifically in front of the mouth of the estuary of the Patos Lagoon. The data allowed observing acoustic anomalies characterized like being a response to gas presence in the sediment. The gas accumulations were identified based on their morphology, dimension, type of acoustic signature and apparent concentration of gas. Thus, five different features of shallow gas were recognized: gas curtain, acoustic blanking, acoustic turbidity zone, turbidity pinnacle and intra-sedimentary plume. These structures have been isolated or then related each other. Among these, the gas curtain and acoustic blanking were those that occurred in greater number and area. Gas curtains presented well defined morphology, in gas boxes format, where the gas is more concentrated. Acoustic blacking, originated from presence of well disseminated gas bubbles in the sediment, was distinguished by a strong top reflection that masks the below reflectors, without to show well defined lateral limits Acoustic turbidity zone, associated with the dissemination of moderate to high gas, is a signal disturbance due to the presence of bubbles in the sediment in quantities that only attenuate the seismic energy, allowing yet identifying some reflector below its top. Turbidity pinnacles found are small and present pointed shape, indicating to a low to moderated gas dissemination. Intra-sedimentary plume found presented an almost parabolic shape, penetrating across the sediment layer thus the gas dissemination in the plume is low to moderate. These forms are linked directly with the sedimentary facies distribution, which act like reservoir and sealant, retaining or not the gas and producing the distinct acoustic response. The gas is concentrated in front of the mouth of Patos Lagoon, deposition site of fine sediments and organic matter. Such lagoon sediment input and the reworking of the shelf by marine regression and transgression events during Quaternary allowed the genesis and preservation of gas occurring in the Holocene sediments, which origin is probable biogenic.

Seismic traveltime inversion, traveltime tomography and seismic reflection techniques have been applied for two dimensional (2D) and three dimensional (3D) data acquired in conjunction with site characterization and monitoring aspects at a carbon dioxide (CO2) geological storage site at Ketzin, Germany (the CO2SINK project). Conventional seismic methods that focused on investigating the CO2 storage and caprock formations showed a poor or no image of the upper 150 m. In order to fill this information gap, an effort on imaging the shallow subsurface at a potentially risky area at the site is the principal goal of this thesis. Beside this objective, a seismic source comparison from a 2D pilot study for acquisition parameter testing at the site found a weight drop source suitable with respect to the signal penetration, frequency content of the data and minimizing time and cost for 3D data acquisition. For the Ketzin seismic data, the ability to obtain high-quality images is limited by the acquisition geometry, source-generated noise and time shifts due to near-surface effects producing severe distortions in the data. Moreover, these time shifts are comparable to the dominant periods of the reflections and to the size of structures to be imaged. Therefore, a combination of seismic refraction and state-of-the-art processing techniques, including careful static corrections and more accurate velocity analysis, resulted in key improvements of the images and allowed new information to be extracted. The results from these studies together with borehole information, hydrogeologic models and seismic modeling have been combined into an integrated interpretation. The boundary between the Quaternary and Tertiary unit has been mapped. The internal structure of the Quaternary sediments is likely to be complicated due to the shallow aquifer/aquitard complex, whereas the heterogeneity in the Tertiary unit is due to rock alteration associated with fault zones. Some of the major faults appear to project into the Tertiary unit. These findings are important for understanding the potentially risky anticline crest and can be used as a database for the future monitoring program at the site.

<p>Seismic traveltime inversion, traveltime tomography and seismic reflection techniques have been applied for two dimensional (2D) and three dimensional (3D) data acquired in conjunction with site characterization and monitoring aspects at a carbon dioxide (CO₂) geological storage site at Ketzin, Germany (the CO₂SINK project). Conventional seismic methods that focused on investigating the CO₂ storage and caprock formations showed a poor or no image of the upper 150 m. In order to fill this information gap, an effort on imaging the shallow subsurface at a potentially risky area at the site is the principal goal of this thesis.</p><p>Beside this objective, a seismic source comparison from a 2D pilot study for acquisition parameter testing at the site found a weight drop source suitable with respect to the signal penetration, frequency content of the data and minimizing time and cost for 3D data acquisition.</p><p>For the Ketzin seismic data, the ability to obtain high-quality images is limited by the acquisition geometry, source-generated noise and time shifts due to near-surface effects producing severe distortions in the data. Moreover, these time shifts are comparable to the dominant periods of the reflections and to the size of structures to be imaged. Therefore, a combination of seismic refraction and state-of-the-art processing techniques, including careful static corrections and more accurate velocity analysis, resulted in key improvements of the images and allowed new information to be extracted. The results from these studies together with borehole information, hydrogeologic models and seismic modeling have been combined into an integrated interpretation. The boundary between the Quaternary and Tertiary unit has been mapped. The internal structure of the Quaternary sediments is likely to be complicated due to the shallow aquifer/aquitard complex, whereas the heterogeneity in the Tertiary unit is due to rock alteration associated with fault zones. Some of the major faults appear to project into the Tertiary unit. These findings are important for understanding the potentially risky anticline crest and can be used as a database for the future monitoring program at the site.</p>

Investigating the archaeology of submerged landscapes beneath many metres of sea and buried under modern sands requires an understanding of the terrestrial surface as it may have been prior to the inundation. To do this, environmental evidence is required from contextualised in-situ locations and the best material evidence for preservation of archaeology, organic remains, dating proxies, pollen, diatoms, microfossils, coleoptera etc. is peat. This research supports the search for peat in submarine environments by interpreting seismic surveys of the sub-sea floor and analysing reflective signals for distinctive organic responses. By means of sedimental analysis and ground observation, the research sets out to differentiate between organic signals, to allow for the identification and location of shallow peat beds within features of a palaeolandscape. Using these results should provide an opportunity to target such peat beds in an archaeologically focused coring programme. The research also examines ways in which organic responses may be mapped over larger areas in order to integrate the results into a wider scale landscape model identifying potential peatland, marsh, valley fen and lowland areas. Finally, the research introduces an artificial intelligence neural networking technology for the identification of organic interfaces in seismic surveys, examining three different ways in which this could be accomplished using specialist computer tools and software.

Geophysical research has long been interdisciplinary, with many phenomena on the Earth's surface involving multiple, linked processes that are best understood using a combination of techniques. This is particularly true in the case of grain flows on sand dunes, in which the sedimentary stratification with which geologists are concerned arises from the granular processes investigated by physicists and engineers, and the water permeation that interests hydrologists and soil scientists determines the seismic velocities of concern to exploration geophysicists. In this dissertation, I describe four projects conducted for the degree of Doctor of Philosophy, using a combination of laboratory experimentation, fieldwork, numerical simulation, and mathematical modelling to link avalanching on dunes to its effects on stratification, on the permeation of water, and on seismic surveys. Firstly, I describe experiments on erodible, unbounded, grain piles in a channel, slowly supplied with additional grains, and I demonstrate that the behaviour of the consequent, discrete avalanches alternates between two regimes, typified by their size statistics. Reconciling the `self-organised criticality' that several authors have predicted for such a system with the hysteretic behaviour that others have observed, the system exhibits quasi-periodic, system-spanning avalanches in one regime, while in the other avalanches pass at irregular intervals and have a power-law size distribution. Secondly, I link this power-law size distribution to the strata emplaced by avalanches on bounded grain piles. A low inflow rate of grains into an experimental channel develops a pile, composed of strata in which blue-dyed, coarser grains overlie finer grains. Associating stopped avalanche fronts with the `trapped kinks' described by previous authors, I show that, in sufficiently large grain piles, mean stratum width increases linearly with distance downslope. This implies the possibility of interpreting paleodune height from the strata of aeolian sandstones, and makes predictions for the structure of avalanche-associated strata within active dunes. Thirdly, I discuss investigations of these strata within active, Qatari barchan dunes, using dye-infiltration to image strata in the field and extracting samples across individual strata with sub-centimetre resolution. Downslope increases in mean stratum width are evident, while measurements of particle size distributions demonstrate preferential permeation of water along substrata composed of finer particles, explaining the strata-associated, localised regions of high water content discovered by other work on the same dunes. Finally, I consider the effect of these within-dune variations in water content on seismic surveys for oil and gas. Having used high performance computing to simulate elastic wave propagation in the vicinity of an isolated, barchan sand dune, I demonstrate that such a dune acts as a resonator, absorbing energy from Rayleigh waves and reemitting it over an extensive period of time. I derive and validate a mathematical framework that uses bulk properties of the dune to predict quantitative properties of the emitted waves, and I demonstrate the importance of internal variations in seismic velocity, resulting from variations in water content.