Dissertations / Theses: 'Seismology and Seismic Exploration'

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Brannon, Brittany Ann. "Faulty Measurements and Shaky Tools: An Exploration into Hazus and the Seismic Vulnerabilities of Portland, OR." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/1410.

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Events or forces of nature with catastrophic consequences, or "natural disasters," have increased in both frequency and force due to climate change and increased urbanization in climate-sensitive areas. To create capacity to face these dangers, an entity must first quantify the threat and translate scientific knowledge on nature into comprehensible estimates of cost and loss. These estimates equip those at risk with knowledge to enact policy, formulate mitigation plans, raise awareness, and promote preparedness in light of potential destruction. Hazards-United States, or Hazus, is one such tool created by the federal government to estimate loss from a variety of threats, including earthquakes, hurricanes, and floods. Private and governmental agencies use Hazus to provide information and support to enact mitigation measures, craft plans, and create insurance assessments; hence the results of Hazus can have lasting and irreversible effects once the hazard in question occurs. This thesis addresses this problem and sheds light on the obvious and deterministic failings of Hazus in the context of the probable earthquake in Portland, OR; stripping away the tool's black box and exposing the grim vulnerabilities it fails to account for. The purpose of this thesis is twofold. First, this thesis aims to examine the critical flaws within Hazus and the omitted vulnerabilities particular to the Portland region and likely relevant in other areas of study. Second and more nationally applicable, this thesis intends to examine the influence Hazus outputs can have in the framing of seismic risk by the non-expert public. Combining the problem of inadequate understanding of risk in Portland with the questionable faith in Hazus alludes to a larger, socio-technical situation in need of attention by the academic and hazard mitigation community. This thesis addresses those issues in scope and adds to the growing body of literature on defining risk, hazard mitigation, and the consequences of natural disasters to urban environments.

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Gillet, Kévin. "Explorer les hétérogénéités de petite échelle de la lune et de la terre." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30310/document.

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Au cours de leur propagation, les ondes sismiques sont atténuées par deux phénomènes : l'absorption causée par les propriétés anélastiques des matériaux, d'une part, et la diffusion ou " scattering " causée par la présence d'hétérogénéités de petite échelle dans le milieu d'autre part. L'objectif de cette thèse est de cartographier les propriétés de diffusion et d'absorption des ondes sismiques dans deux contextes géophysiques extrêmes présentant des échelles spatiales très différentes. La première partie du manuscrit est consacrée à la stratification d'hétérogénéité dans la Lune. À l'aide d'un modèle original de diffusion en géométrie sphérique, nous avons inversé les mesures de temps d'arrivée du maximum d'énergie et de décroissance de la coda sismique réalisée sur les données des missions Apollo. Nos inversions mettent en évidence un très fort contraste des propriétés de scattering entre le mégarégolithe très atténuant et le manteau lunaire profond transparent. L'atténuation est très largement dominée par le scattering et suggère la présence de fracturation jusqu'à environ 100 km de profondeur, affectant ainsi le manteau. Une nouvelle méthode d'estimation de la profondeur des séismes superficiels fondée sur les signaux diffus a été développée et permet de confirmer l'existence de failles actives autour de 50 km de profondeur. La deuxième partie de la thèse est consacrée à la structure d'atténuation de Taïwan, une région qui présente des structures géologiques très variées dans un contexte tectonique de double subduction. On utilise la MLTWA (Multiple Lapse Time Window Analysis) -une méthode fondée sur le rapport entre énergie cohérente et incohérente du signal sismique- pour imager les variations latérales d'atténuation. Dans un premier temps nous avons travaillé dans l'hypothèse classique de diffusion isotrope dans un demi-espace. Nos résultats mettent en évidence un niveau d'atténuation globale très élevé ainsi que de forts contrastes des propriétés de scattering sur des échelles spatiales fines, de l'ordre de 10-20 km. La diffusion est particulièrement marquée dans les bassins de la côte ouest, le sud et la chaîne côtière associée à la collision avec l'arc volcanique de Luçon à l'est. L'absorption augmente graduellement vers l'est et atteint son maximum sous l'arc volcanique. L'examen de l'accord entre données et modèles a posteriori montre sans ambiguïté les limites de l'hypothèse de diffusion isotrope dans un demi-espace sur un ensemble de stations situées le long des côtes. Ceci nous conduit à explorer les effets de la diffusion anisotrope dans un guide d'onde modélisant la croûte. La prise en compte de l'anisotropie améliore significativement l'accord du modèle aux données. En particulier, à basse fréquence (1-2 Hz), notre étude démontre la prédominance de rétro-diffusion. Ce résultat est compatible avec la présence de forts contrastes d'impédance dans la croûte et suggère la présence massive de fluides dans les zones de failles et de volcans à Taïwan. La mesure de l'anisotropie de la diffusion ouvre des perspectives nouvelles de caractérisation des hétérogénéités géophysiques de petite échelle
During their propagation, seismic waves are attenuated by two phenomena: on one hand, absorption caused by the anelastic properties of the materials, and on the other hand, scattering caused by the presence of small-scale heterogeneities in the medium. The aim of this thesis is to map the properties of scattering and absorption of seismic waves in two extreme geophysical contexts with very different spatial scales. The first part of this memoir is devoted to the stratification of heterogeneities in the Moon. We use a new diffusion model in spherical geometry to invert measurements of the time of arrival of the maximum of energy and the seismic coda decay on data from the Apollo missions. Our inversions provide evidence of a very sharp contrast of scattering properties between the highly attenuating megaregolith and the transparent deep lunar mantle. Attenuation is largerly dominated by scattering and suggests the presence of fractures down to about 100 km depth, into the mantle. A new method for estimating the depth of shallow moonquakes based on diffusive signals was developped and confirms the existence of active faults around 50 km deep. The second part of this thesis is devoted to the attenuation structure of Taiwan, a region with a wide variety of geological structures in the context of two subduction zones. We use the MLTWA (Multiple Lapse Time Window Analysis) -a method based on the ratio between the coherent and incoherent energy of the seismic signal- to image the lateral variations of attenuation. We worked first with the classical hypothesis of isotropic scattering in a half-space. Our results provide evidence for a globally high level of attenuation with sharp contrasts of scattering properties across small spatial scales, of the order of 10-20 km. Scattering is particularly strong in the basins of the west coast, southern Taiwan and the eastern Coastal Range associated with the collision with the Luzon volcanic arc. Absorption increases gradually eastwards and reaches a maximum below the volcanic arc. A posteriori examination of the fit between data and model shows unambiguously the limits of the hypothesis of isotropic scattering in a half-space for a number of stations located along the coasts. This leads us to explore the effects of anisotropic scattering in a guide for seismic waves representing the crust. Taking anisotropy into account significantly improves the fitness of the model to the data. In particular, at low frequency (1-2 Hz), our study shows the prevalence of backscattering. This result is compatible with the presence of sharp contrasts of impedance in the crust and suggests the strong presence of fluids in fault zones and volcanoes in Taiwan. The measurement of scattering anisotropy opens new perspectives for characterizing small-scale geophysical heterogeneities

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Masoni, Isabella. "Inversion of surface waves in an oil and gas exploration context." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAU029/document.

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La caractérisation de la proche surface est un enjeu majeur pour l'industrie pétrolière. Lors des acquisitions terrestres et Ocean Bottom Cable (OBC), les couches superficielles généralement altérées ou peu consolidées, présentent des structures géologiques complexes et ont éventuellement des variations topographiques importantes. Les ondes de surface, énergétiques, se propagent dans ce milieu complexe et dominent les sismogrammes, ce qui masque le signal utile pour le traitement sismique classique et rend difficile l'imagerie à la profondeur du réservoir.Il est donc important de pouvoir atténuer ces ondes, éventuellement d'appliquer des corrections statiques et/ou d'amplitude. Ceci qui nécessite une connaissance précise du modèle de vitesse de la proche surface. L'étude de la dispersion des ondes de surface est couramment utilisée en sismologie globale et à l'échelle géotechnique pour évaluer les propriétés des milieux terrestres. Il existe néanmoins des limitations: la mesure de cette dispersion est souvent difficile et les profils de vitesses obtenus sont 1D. A l'échelle pétrolière, l'hypothèse 1D n'est pas toujours adaptée, ce qui motive l'utilisation d'une méthode alternative d'imagerie plus haute résolution, la méthode d'inversion de la forme d'onde (FWI). Cependant, le modèle de vitesse initial doit être assez précis pour éviter le "cycle-skipping" et permettre la convergence vers la solution optimale.Cette étude explore différentes alternatives de fonctions coûts pour résoudre le "cycle-skipping" et diminuer la dépendance de l'inversion à la qualité du modèle initial. En exprimant les fonctions coûts dans le domaine f-k (fréquence-nombre d'onde) et le domaine f-p (fréquence-lenteur), la FWI est plus robuste. A l'aide d'exemples synthétiques, nous démontrons l'efficacité de ces nouvelles approches qui permettent bien de retrouver les variations latérales de vitesses d'onde S.Dans une seconde partie, nous développons une inversion FWI en "layer stripping", adaptée spécifiquement à la physique des ondes de surface. Comme la profondeur de pénétration de ces ondes dépend de leur longueur d'onde, et donc, de leur contenu fréquentiel, nous proposons d'inverser séquentiellement des plus hautes aux plus basses fréquences de ces ondes pour contraindre successivement les couches superficielles jusqu'aux plus profondes. Un fenêtrage selon la distance source-station est également appliqué. Dans un premier temps seules les courtes distances sont inversées, au fur à mesure les données associées à des plus grandes distances sont rajoutées, plus fortement impactées par le "cycle-skipping". Nous démontrons à l'aide d'exemples synthétiques l'avantage de cette méthode par rapport aux méthodes multi-échelles conventionnelles inversant des basses vers les hautes fréquences.Enfin, l'inversion des ondes de surface pour la caractérisation de la proche surface est confrontée à un cas réel. Nous discutons la construction et la pertinence du modèle initial et les difficultés rencontrées lors de l'inversion
The characterization of the near surface is an important topic for the oil and gas industry. For land and Ocean Bottom Cable (OBC) acquisitions, weathered or unconsolidated top layers, prominent topography and complex shallow structures may make imaging at target depth very difficult. Energetic and complex surface waves often dominate such recordings, masking the signal and challenging conventional seismic processing. Static corrections and the painstaking removal of surface waves are required to obtain viable exploration information.Yet surface waves, which sample the near surface region, are considered as signal on both the engineering and geotechnical scale as well as the global seismology scale. Their dispersive property is conventionally used in surface wave analysis techniques to obtain local shear velocity depth profiles. But limitations such as the picking of dispersion curves and poor lateral resolution have lead to the proposal of Full Waveform Inversion (FWI) as an alternative high resolution technique. FWI can theoretically be used to explain the complete waveforms recoded in seismograms, but FWI with surface waves has its own set of challenges. A sufficiently accurate initial velocity model is required or otherwise cycle-skipping problems will prevent the inversion to converge.This study investigates alternative misfit functions that can overcome cycle-skipping and decrease the dependence on the initial model required. Computing the data-fitting in different domains such as the frequency-wavenumber (f-k) and frequency-slowness (f-p) domains is proposed for robust FWI, and successful results are achieved with a synthetic dataset, in retrieving lateral shear velocity variations.In the second part of this study a FWI layer stripping strategy, specifically adapted to the physics of surface waves is proposed. The penetration of surface waves is dependent on their wavelength, and therefore on their frequency. High-to-low frequency data is therefore sequentially inverted to update top-to-bottom layer depths of the shear velocity model. In addition, near-to-far offsets are considered to avoid cycle-skipping issues. Results with a synthetic dataset show that this strategy is more successful than conventional multiscale FWI in using surface waves to update the shear velocity model.Finally inversion of surface waves for near surface characterization is attempted on a real dataset at the oil and gas exploration scale. The construction of initial models and the difficulties encountered during FWI with real data are discussed

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Hanson, Jeffrey Acton. "Seismic and hydroacoustic investigations near Ascension Island /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823701.

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Harrigan, Edward. "Seismic event tracking." Thesis, University of Strathclyde, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267506.

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Valle, G. Raul del. "Model parameterization in refraction seismology." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66057.

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Sen, Vikramaditya. "A seismic survey in antarctica, parallel schemes for seismic migration and target oriented velocity analysis /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.

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Morgan, Joanna Victoria. "Seismic studies over continental margins." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279659.

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Lee, Delman. "Seismic imaging through inhomogeneous media." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305556.

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Monterroso, Juárez David Aníbal. "Statistical Seismology Studies in Central America : b-value, seismic hazard and seismic quiescence." Doctoral thesis, Uppsala University, Department of Earth Sciences, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3613.

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The present thesis collects results of research applying theory and methods of statistical seismology to the seismicity of Central America, a region with a complex tectonic setting controlled by the interaction of four major plates, namely the Caribbean, Cocos, Nazca and North American plates.

Three different earthquake catalogues were used for studies focused on stress in a tectonic volume, seismic hazard maps and seismicity patterns (precursors), covering the region 94ºW to 81ºW and 5ºN to 20ºN.

Variations in the b-value, the parameter in Gutenberg & Richter’s equation LogN=a-bM, as a function of depth in the subduction zone were investigated. High b-values were identified in the upper part of the slab at depths of 80-110km beneath Guatemala-El Salvador and at depths 130-170km beneath Nicaragua. These anomalies may be related to the generation of volcanism occurring above them. Time dependence of the b-value was also studied. Five case studies were selected (events with MS ≥7.2) for a detailed analysis. In three out of five cases, it was possible to link b-value minima to the time of occurrence of corresponding large events.

Seismic quiescence was mapped as a function of time and space by a griding technique. The characteristics of the quiescence were calculated using the statistics Z and ß and for Time Window lengths between 1 and 5 years. Five positive anomalies were found, which can be associated with large earthquakes (MS≥7.2).

Finally, a Monte Carlo approach was utilized to evaluate the ground motion hazard and its uncertainties in northern Central America. A set of new seismic hazard maps exhibiting probabilistic values of peak ground acceleration (PGA) with 50%, 10%, and 5% probabilities of exceedance (PE) in 50 years is presented for a large area of northern Central America, including El Salvador and Guatemala.

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Leipski, Elizabeth A. "Analytical investigation of In Situ Seismic methods." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/19002.

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Demere, Judith Arlene. "Attenuation of seismic waves in Alabama." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/25957.

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Brittan, John. "Veracity of wide-angle seismic data." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309316.

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Rowbotham, Peter S. "Advances in crosshole seismic reflection processing." Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5760/.

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In recent years there have been significant advances in the acquisition and processing of crosshole seismic reflection data, and the method has been shown to be a high resolution imaging technique. However, the fidelity of the final images produced by this technique needs to be considered carefully to avoid incorrect interpretation. This thesis concerns the imaging capability of crosshole surveys, as well as advances made in processing techniques for application to crosshole seismic reflection surveys. In a migrated seismic section, a meaningful image is only obtained if a range of dips around the local structural dip is sampled at each image point. For crosshole seismic reflection surveys, the distribution of dips sampled at an image point is controlled principally by the survey geometry, including source and receiver array lengths and their element spacings. By considering the dips sampled, the imaging capability of crosshole reflection surveying is discussed, with suggestions as to how to ensure optimal imaging of the target zone. To overcome problems encountered in applying standard processing procedures, two new processing techniques are presented which enhance the imaging potential of crosshole reflection seismics. Generalised Berryhill migration has been developed as a full generalised Kirchhoff migration to include the near-field term, with the aim of improving image accuracy close to the source and receiver arrays. 3-D f-k-k filtering is an improved method of wavefield separation for crosshole seismic data. Finally, the results of processing three types of dataset are presented. One is from a site in the Groningen gas field, another was acquired through a model interrogated at ultrasonic frequencies in a water tank, and the third type was acquired using coal exploration boreholes in Yorkshire. The results demonstrate the imaging capability of the crosshole reflection method, and the success of the two new processing schemes.

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Harith, Zuhar Zahir Tuan. "New methods in shallow seismic reflection." Thesis, University of Glasgow, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284735.

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Coates, Richard T. "On the scattering of seismic waves." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335705.

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Lewis, Anthony H. J. "The deep seismic structure of northern England and adjacent marine areas from the Caledonian Suture Seismic project." Thesis, Durham University, 1986. http://etheses.dur.ac.uk/7088/.

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This thesis describes the interpretation of the deep seismic structure from the wide-angle reflection/refraction Caledonian Suture Seismic experiment which extends from the Mid North Sea High across Northern England, the Irish Sea to southwest Ireland. A new method of displaying the large number of travel times in the form of contoured composite plots for a particular phase has been developed. The interpretation methods used include analysis of the wide-angle reflection travel times, time-term analysis, gravity modelling, and, ray tracing and synthetic seismogram modelling. A mid-crustal gradient which returns PcP occurs between depths of 15.0-18.5 km beneath the line and is overlain by an upper crust with an average velocity of 6.16-6.20 km/s excluding sediments. This mid-crustal gradient was not recognised previously in the Irish Sea. A lower-crustal boundary recognised from the PmP phase occurs at 25.0 km depth beneath the Irish Sea and at 30 km beneath the North Sea. The average crustal velocity is 6.49-6.54 km/s excluding sediments and for the lower crust is 6.75-6.77 km/s. The sub-Moho Pn velocity is estimated to be 8.19 km/s beneath the Irish Sea, 8.32 km/s beneath Northern England and 8.02 km/s beneath the North Sea. The PmP and Pn boundaries diverge beneath the Irish Sea and define a transitional Moho over a 5 km depth range with an average velocity of 7.8-7.9 km/s. The PcP and Pn boundaries correspond approximately with the top and base respectively of the reflective deep crust observed beneath the Irish Sea on BIRPS WINCH. The transitional Moho beneath the Irish Sea has a reflective character similar to the lower crust. The coincident PmP and Pn boundaries beneath the North Sea define an abrupt increase in velocity from 6.75 to 8.0 km/s which approximately corresponds to the prominent reflections beneath the non reflective lower crust observed on the BIRPS NEC line at 10.5 to 11.0 s .The upper crust of velocity 6.15-6.20 km/s appears to lie below the suture beneath Northern England and the North Sea along the line but may also occur above it further west. The lower crust and deeper structures lie below the suture and represent crust of the Southern Caledonides. The anomalous structure of the Moho and upper mantle beneath the Irish Sea found from CSSP and BIRPS may be related to the post-Caledonian formation of the Irish Sea basins. The reflective lower crust and transitional Moho may result from crustal thinning produced by ductile stretching.

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Jones, Kevin Alun. "Crustal inferences from multi-offset seismic data." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267855.

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Portsmouth, Ian Robert. "Field studies of seismic attenuation and scattering." Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296850.

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Le, Bougeant Michel. "Reflection seismic processing in transversely isotropic media." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300086.

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Zolfaghari, Mohammad Reza. "GIS-based seismic hazard assessment of Iran." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299902.

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Hu, Tianyue. "Decomposition of seismic wavefields and its applications." Thesis, Birkbeck (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390193.

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Demir, Ismail. "Seismic wave modelling using finite difference methods." Thesis, University of South Wales, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284896.

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Smith, Sonya K. "Assessing the quality of deep seismic data." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361690.

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Roberts, Graham. "Shear-wave polarizations from local seismic events." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/14293.

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Jones, Neil. "Seismic anisotropy and heterogeneity of young Atlantic crust." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240090.

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Loveridge, M. M. "Marine seismic source signatures : directivity and the ghost." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355760.

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Eddies, Roderick David. "An investigation of seismic attenuation in marine sediments." Thesis, University of Plymouth, 1994. http://hdl.handle.net/10026.1/2109.

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There have been relatively few investigations into the attenuation properties of unconsolidated sediments using marine surface seismic data. Several methods of measuring attenuation were assessed for reliability in a noise-free case and with the addition of noise using a set of synthetically absorbed and dispersed wavelets. Wavelet modelling proved to be superior to the other techniques, followed by spectrum modelling and the spectral ratios method. Complex trace analysis using the analytical signal proved to be unreliable for non-sinusoidal wavelets, whilst the risetime method was found to be very susceptible to noise for practical purposes. Numerical modelling was carried out to assess the spectral effects of layering on a propagating pulse. The thin layer / peg-leg phenomenon has varying filtering effects on the propagating pulse. In particular, layers which are less than the "tuning thickness" of the propagating pulse have a low-pass effect. The quality factor, Q, was measured in two case studies. In the first, the mean Q was determined from wavelet and spectrum modelling and found to be 60 for fine sands and 47 for coarse sands in the 1 kHz to 3 kHz frequency band. In the second, Q was determined as 59 for poorly sorted sandy diamicts in the 100 Hz to 240 Hz frequency band. The close fit between synthesised spectra and wavelets and observed data showed that a constant- Q mechanism would account for the spectral changes between the seabed and the deeper target reflection events in the two case studies. The spectra of the target reflection events in both case studies were lacking in low frequencies which is likely to be due to low-pass filtering from composite reflection events due to thin bed layering. For practical purposes, the determination of Q from a mean normalised seismic trace yielded the same result as measuring a mean Q from individual traces. In a third case study, the seabed multiple was compared to the seabed reflection using wavelet and spectrum modelling. A lack of low frequencies in the seabed multiple showed that the seabed can act as a low-pass filter to an incident pulse. As the numerical methods rely on the seabed as having a white reflection and transmission response, the low-pass effect will result in erroneous estimates of the quality factor, Q.

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Brooks, S. G. "Seismic velocities from crustal sections in Northern Scandinavia." Thesis, University of East Anglia, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372358.

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Henry, William John. "A seismic investigation of the Kenya Rift Valley." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/35038.

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In August of 1985 the crustal structure underlying the Kenya rift valley was investigated by long range explosion seismology. The experiment (KRISP85) consisted of two seismic lines in the central sector of the rift, one along the axis (140 km) and the other across it (50 km). Interpretation of the data, including time-term analysis and ray tracing has yielded the following information. The thickness of rift infill varies from about 6 km below Lake Naivasha to about 2 km and 1.5 km below Lake Magadi and Lake Bogoria respectively. The underlying material has a P-wave velocity of 6.05 +/- 0.03 km/s which suggests the rift is underlain by Precambrian metamorphic basement. A localised high velocity zone identified to the east of Nakuru may be associated with basic intrusive material. The P-wave velocity increases discontinuously to 6.45 +/- 0.05 km/s at a depth of 12.5 +/- 1-0 km. This depth is similar to that inferred for the brittle-ductile transition zone from a study of local seismicity in the Lake Bogoria region. A high P-wave velocity layer (7.1 +/- 0.15 km/s) occurs at 22 +/- 2 km depth which might be associated with a sill-like basic intrusion in the lower crust. An upper mantle velocity of 7.5 +/- 0.2 km/s (unreversed) is reached at a depth of 34.0 +/- 2.0 km. This implies that only moderate crustal attenuation has occurred beneath the central sector of the rift. No evidence was obtained for the existence of an "axial intrusion" reaching to shallow levels below the rift and causing crustal separation as suggested by previous studies. Relative residuals determined for 46 teleseismic events recorded by a 15 station, small aperture seismic array in the vicinity of Lake Bogoria indicate considerable lateral heterogeneity in the upper crust. An Aki inversion of the relative residuals has revealed the existence of two distinct low velocity zones which may be associated with magma chambers.

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Craig, Mitchell Scott. "A discreet-scatterer model of the seismic P coda." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/25858.

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Alberts, Ernst Patrick. "Horizon mapping in exploration seismology using artficial intelligence." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272160.

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Willemsen, Lucas Abraham. "Problems with a localized nature in exploration seismology." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108840.

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Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 267-274).
A wide range of problems in seismology have a localized nature. Examples include inversion for time-lapse change, salt boundary position and Amplitude or Phase Versus Angle (AVA/PVA). With increasing computational power, many inversion procedures have transitioned away from forward models with simplified physics and now simulate synthetic wavefields on a model representation of the Earth. These simulated wavefields form the basis for the model updates in the inversion. Usually these wavefields are simulated on the entire computational model, even though the region of interest and the associated updates of the computational model are localized. In this thesis I explore ways of making use of the localized nature of the inversion by limiting the wavefield generation to the region of interest. This shrinking of the computational domain leads to faster solutions, reducing the time between the start and finish of the local inversion. This shorter turn-around time facilitates decision making and improves the interactivity of the inversion procedure. I first introduce a frequency domain local solver which can generate exactly the same wavefields as a full domain solver. I then apply this local solver to both a time-lapse problem and to salt boundary inversion. I then take a step back and look at time-lapse inversion outside the scope of local solvers. By looking at differences in the Full Waveform Inversion (FWI) gradient obtained from baseline and monitor datasets I compute a confidence map of locations likely to contain time-lapse change. This confidence map is then used to regularize a joint inversion for both the baseline and monitor datasets. I compare this methodology to other existing time-lapse algorithms on a synthetic North Sea model. In this study I notice the importance of post-critical reflections and become aware of their potential for reservoir characterization. Motivated by this observation I introduce a local solver for simulating elastic reflections in a region of interest. These elastic reflections can then be used for AVA and PVA to for instance invert for reservoir characteristics. The wavefield is efficiently propagated through the overburden using precomputed acoustic Green's functions obtained from a cheap acoustic solver.
by Lucas Abraham (Bram) Willemsen
Ph. D. in Geophysics

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34

Williamson, P. R. "Tomographic inversion of traveltime data in reflection seismology." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383956.

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Henton, Joseph Alan. "GPS studies of crustal deformation in the northern Cascadia subduction zone." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0020/NQ48226.pdf.

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36

Scott, James B. "Seismic noise in the shallow subsurface methods for using it in earthquake hazard assessment /." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3258847.

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Kirk, Wayne John. "Seismic and potential field studies over the East Midlands." Thesis, University of Leicester, 1989. http://hdl.handle.net/2381/35054.

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A seismic refraction profile was undertaken to investigate the source of an aeromagnetic anomaly located above the Widmerpool Gulf, East Midlands. Ten shots were fired into 51 stations at c. 1.5km spacing in a 70km profile during 41 days recording. The refraction data were processed using standard techniques to improve the data quality. A new filtering technique, known as Correlated Adaptive Noise Cancellation was tested on synthetic data and successfully applied to controlled source and quarry blast data. Study of strong motion data reveals that the previous method of site calibration is invalid. A new calibration technique, known as the Scaled Amplitude method is presented to provide safer charge size estimation. Raytrace modelling of the refraction data and two dimensional gravity interpretation confirms the presence of the Widmerpool Gulf but no support is found for the postulated intrusion. Two dimensional magnetic interpretation revealed that the aeromagnetic anomaly could be modelled with a Carboniferous igneous source. A Lower Palaeozoic refractor with a velocity of 6.0 km/s is identified at a maximum depth of c. 2.85km beneath the Widmerpool Gulf. Carboniferous and post-Carboniferous sediments within the gulf have velocities between 2.6-5.5 km/s with a strong vertical gradient. At the gulf margins, a refractor with a constant velocity of 5.2 km/s is identified as Dinantian limestone. A low velocity layer of proposed unaltered Lower Palaeozoics is identified beneath the limestone at the eastern edge of the Derbyshire Dome. The existence and areal extent of this layer are also determined from seismic reflection data. Image analysis of potential field data, presents a model identifying 3 structural provinces, the Midlands Microcraton, the Welsh and English Caledonides and a central region of complex linears. This model is used to explain the distribution of basement rocks determined from seismic and gravity profiles.

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Wang, Yanghua. "Co-operative inversion of seismic traveltime and amplitude data." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267299.

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Totterdell, Ian John. "Lower-crustal velocities from long-offset seismic reflection data." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259655.

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Linneman, Dorothy. "The EGS Collab Hydrofracture Experiment: Seismic Velocity and Elastic Moduli Characterization." Scholarship @ Claremont, 2019. https://scholarship.claremont.edu/scripps_theses/1240.

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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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Li, Dekun. "Seismic hazard analysis for bridge design in the Hong Kong region /." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23436049.

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Herrmann, Felix J. "Seismology meets compressive sampling." Institute for Pure & Applied Mathematics. University of California, Los Angeles, 2007. http://hdl.handle.net/2429/603.

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43

Zheng, York Yao. "Time-lapse seismic imaging using elastic full waveform inversion of ocean-bottom cable data." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648657.

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Stek, Ivan. "Frequency domain seismic forward modelling : a tool for waveform inversion." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267748.

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Herwanger, Jorg. "Seismic and electric crosshole tomography for fracture detection and characterization." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367577.

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McDonald, Robert John. "The application of shallow seismic reflection to onshore quaternary studies." Thesis, Cardiff University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250747.

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Powell, C. M. R. "A wide-angle, multichannel seismic study of the continental lithosphere." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233313.

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Previous experiments to record seismic data at wide angle on the continental shelf have generally been unsuccessful in determining velocity structure in the lower crust; either the lines were too short or shot-receiver density too sparse to identify lower crustal arrivals. In contrast, deep normal incidence profiles show good structural resolution in the crust and uppermost mantle. This dissertation describes a new sea-bottom multichannel instrument which was developed to record datasets containing closely spaced traces to improve the resolution of reversed wide-angle experiments on the continental shelf. The Pull-Up Multichannel Array (PUMA) is a 1200 m, 12 channel, hydrophone array for remotely recording seismic data on the sea-bed. It consists of 12 short hydrophone sections linked by 100 m long passive sections. A pressure case is attached at one end in which recording electronics, cassette tape recorders and a battery power supply are housed. The PUMA is deployed in less than 200 m of water from a research ship and moored to buoys for recovery. The instrument, which was successfully used in an experiment west of Lewis, Outer Hebrides, U.K., was specifically designed to determine a well constrained velocity structure for the crust and uppermost mantle over part of the BIRPS WINCH deep, normal incidence profile. Data recorded by the PUMA show a high signal to noise ratio and it is easy to correlate phases across the record section and to monitor changes in amplitude because traces are closely spaced. A velocity structure for the continental crust and uppermost mantle has been devised using amplitude modelling. The model is interpreted to show that: the upper crust consists of Lewisian gneiss metamorphosed in the amphibolite facies, and contains a low velocity zone which is probably granitic in composition; the middle crustal layer has virtually no velocity gradient; and the lower crust, represented by second arrivals, contains a high velocity gradient and probably consists of granulites. The Moho is at 27.0 ± 0.5 km depth. This is shown to be a layered boundary and it is suggested that this layering is caused by crustal underplating. There is little velocity gradient in the uppermost mantle. This model shows good agreement with the BIRPS WINCH section, although the Moho appears to coincide with the top rather than the base of a band of reflections at 8.3 s two-way travel time on unmigrated WINCH data.

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Potts, C. G. "Anomalous seismic structure of the Tydeman and Vema fracture zones." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332744.

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Butcher, J. A. "Seismic stratigraphy of shallow water Quaternary sediments around the UK." Thesis, Bangor University, 1997. https://research.bangor.ac.uk/portal/en/theses/seismic-stratigraphy-of-shallow-water-quaternary-sediments-around-the-uk(0103ae6b-808e-491e-b207-74e648b5ddee).html.

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Tie, An. "On scattering of seismic waves by a spherical obstacle." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/27988.

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Dissertations / Theses on the topic 'Seismology and Seismic Exploration'

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