Dissertations / Theses: 'Seismic wave attenuation'

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Marks, Samantha Georgina. "Seismic wave attenuation from vertical seismic profiles." Thesis, University of Reading, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384872.

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2

Huo, Shoudong. "Wave-equation based seismic multiple attenuation." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/6143.

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Reflection seismology is widely used to map the subsurface geological structure of the Earth. Seismic multiples can contaminate seismic data and are therefore due to be removed. For seismic multiple attenuation, wave-equation based methods are proved to be effective in most cases, which involve two aspects: multiple prediction and multiple subtraction. Targets of both aspects are to develop and apply a fully datadriven algorithm for multiple prediction, and a robust technique for multiple subtraction. Based on many schemes developed by others regarding to the targets, this thesis addresses and tackles the problems of wave-equation based seismic multiple attenuation by several approaches. First, the issue of multiple attenuation in land seismic data is discussed. Multiple Prediction through Inversion (MPTI) method is expanded to be applied in the poststack domain and in the CMP domain to handle the land data with low S/N ratio, irregular geometry and missing traces. A running smooth filter and an adaptive threshold K-NN (nearest neighbours) filter are proposed to help to employ MPTI on land data in the shot domain. Secondly, the result of multiple attenuation depends much upon the effectiveness of the adaptive subtraction. The expanded multi-channel matching (EMCM) filter is proved to be effective. In this thesis, several strategies are discussed to improve the result of EMCM. Among them, to model and subtract the multiples according to their orders is proved to be practical in enhancing the effect of EMCM, and a masking filter is adopted to preserve the energy of primaries. Moreover, an iterative application of EMCM is proposed to give the optimized result. Thirdly, with the limitation of current 3D seismic acquisition geometries, the sampling in the crossline direction is sparse. This seriously affects the application of the 3D multiple attenuation. To tackle the problem, a new approach which applies a trajectory stacking Radon transform along with the energy spectrum is proposed in this thesis. It can replace the time-consuming time-domain sparse inversion with similar effectiveness and much higher efficiency. Parallel computing is discussed in the thesis so as to enhance the efficiency of the strategies. The Message-Passing Interface (MPI) environment is implemented in most of the algorithms mentioned above and greatly improves the efficiency.

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Raji, Wasiu. "Seismic and petro-physical studies on seismic wave attenuation." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/7617/.

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Anelasticity and inhomogeneity in the Earth decreases the energy and modifies the frequency of seismic waves as they travel through the Earth. This phenomenon is known as seismic attenuation. The associated physical process leads to amplitude diminution, waveform distortion and phase delay. The level of attenuation a wave experiences depends on the degree of anelasticity and the scale of inhomgeneity in the rocks it passes through. Therefore, attenuation is sensitive to the presence of fluids, degree of saturation, porosity, fault, pressure, and the mineral content of the rocks. The work presented in this thesis covers attenuation measurements in seismic data; estimation of P- and S-wave attenuation in recorded well logs; attenuation analysis for pore fluid determination; and attenuation compensation in seismic data. Where applicable, a set of 3D seismic data or well logs recorded in the Gullfaks field, North Sea, Norway, is used to test the methods developed in the thesis. A new method for determining attenuation in reflection seismic data is presented. The inversion process comprises two key stages: computation of centroid frequency for the seismic signal corresponding to the top and base of the layer being investigated, using variable window length and fast Fourier transform; and estimation of the difference in centroid frequency and traveltime for the paired seismic signals. The use of a shape factor in the mathematical model allows several wavelet shapes to be used to represent a real seismic signal. When applied to synthetic data, results show that the method can provide reliable estimates of attenuation using any of the wavelet shapes commonly assumed for a real seismic signal. Tested against two published methods of quality factor (Q) measurement, the new method shows less sensitivity to interference from noise and change of frequency bandwidth. The method is also applied to seismic data recorded in the Gullfaks field. The trace length is divided into four intervals: AB, BC, CD, and DE. The mean attenuation (1/Q_m) calculated in intervals AB, BC, CD, and DE are 0.0196, 0.0573, 0.0389, and 0.0220, respectively. Results of attenuation measurements using the new method and the classical spectral ratio method (Bath 1974, Spencer et al, 1982) are in close agreement, and they show that interval BC and AB have the highest and lowest value of attenuation, respectively. One of the applications of Q measured in seismic records is its usage for attenuation compensation. To compensate for the effects of attenuation in recorded seismograms, I propose a Q-compensation algorithm using a recursive inverse Q-filtering scheme. The time varying inverse Q-filter has a Fourier integral representation in which the directions of the up-going and down-going waves are reversed. To overcome the instability problem of conventional inverse Q-filters, wave numbers are replaced with slownesses, and the compensation scheme is applied in a layer-by-layer recursive manner. When tested with synthetic and field seismograms, results show that the algorithm is appropriate for correcting energy dissipation and waveform distortion caused by attenuation. In comparison with the original seismograms, the Q-compensated seismograms show higher frequencies and amplitudes, and better resolved images of subsurface reflectors. Compressional and shear wave inverse quality factors (Q_P^(-1) and Q_S^(-1)) are estimated in the rocks penetrated by well A-10 of the Gullfaks field. The results indicate that the P-wave inverse quality factor is generally higher in hydrocarbon-saturated rocks than in brine-saturated rocks, but the S-wave inverse quality factor does not show a dependence on fluid content. The range of the ratio of Q_P^(-1) to Q_S^(-1) measured in gas, water and oil-saturated sands are 0.56 – 0.78, 0.39 – 0.55, and 0.35 – 0.41, respectively. A cross analysis of the ratio of P-wave to S-wave inverse quality factors, (Q_P^(-1))/(Q_S^(-1) ), with the ratio of P-wave to S-wave velocities, V_P/V_S , clearly distinguishes gas sand from water sand, and water sand from oil sand. Gas sand is characterised by the highest (Q_P^(-1))/(Q_S^(-1) ) and the lowest V_P/V_S ; oil sand is characterised by the lowest (Q_P^(-1))/(Q_S^(-1) ) and the highest V_P/V_S ; and water sand is characterized by the V_P/V_S and (Q_P^(-1))/(Q_S^(-1) ) values between those of the gas and oil sands. The signatures of the bulk modulus, Lame’s first parameter, and the compressional modulus (a hybrid of bulk and shear modulus) show sensitivities to both the pore fluid and rock mineral matrix. These moduli provided a preliminary identification for rock intervals saturated with different fluids. Finally, the possibility of using attenuation measured in seismic data to monitor saturation in hydrocarbon reservoirs is studied using synthetic time-lapse seismograms, and a theoretical rock physics forward modelling approach. The theory of modulus-frequency-dispersion is applied to compute a theoretical curve that describes the dynamic effects of saturation on attenuation. The attenuation measured in synthetic time-lapse seismograms is input to the theoretical curve to invert the saturation that gave rise to the attenuation. Findings from the study show that attenuation measured in recorded seismograms can be used to monitor reservoir saturation, if a relationship between seismogram-derived attenuation and saturation is known. The study also shows that attenuation depends on other material properties of rocks. For the case studied, at a saturation of 0.7, a 10% reduction in porosity caused a 5.9% rise in attenuation, while a 10% reduction in the bulk modulus of the saturating fluids caused an 11% reduction in attenuation.

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Liu, Faqi. "Surface multiple attenuation operators in the plane wave domain : theory and applications /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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Tao, Guo. "Acoustic wave velocities, attenuation and transport properties of some sandstones." Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319154.

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Boadu, Fred Kofi. "Fractal characterization of fractures : effect of fractures on seismic wave velocity and attenuation." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/27272.

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Carpi, Isotta. "Seismic Metamaterials for Rayleigh waves attenuation: analytical and numerical survey on the effect of soil stratification." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.

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Locally resonant materials and periodic media have been recently proposed as a mean to control and redirect elastic waves at different length scale. In particular, at geophysical scale, large resonant/periodic structures have been used as an innovative solution to attenuate the propagation of seismic waves. Previous studies have shown the possibility of attenuating surface ground motions by deflecting seismic Rayleigh waves into soil bulk. This surface to bulk wave conversion has been proved in the case of homogenous soil. Here we investigate how the surface to bulk wave conversion is influenced by inhomogeneous depth dependent soil properties. Analytical and numerical evaluation have been developed in time and frequency domain to determine the efficiency of soil-resonators interaction in inhomogeneous layered media to be used as comparison with experimental results obtained from an experimental setup built at ETH. Furthermore, results from the inhomogeneous case have been compared with the homogenous soil case, to exploit effectiveness and limitation of wave conversion phenomenon. It has been shown that the soil with depth dependent profile strongly influence wave motion. In fact, no effective wave conversion is present in this case, due to stiffer properties of the soil with depth that force the wave to reconvert its direction to the surface.

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Ruan, Youyi. "Surface wave propagation in 3-D anelastic media." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/28945.

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Lateral perturbations in anelasticity (Q) and wave speed together provide important constraints on thermal and chemical structures in the mantle. In present-day tomography studies of global wave speed and anelasticity, the significance of 3-D wave speed and 3-D Q structures on surface wave travel times and amplitudes has not been well understood. In this dissertation, the effects of lateral perturbations in anelasticity (Q) and wave speed on surface wave observables are quantified based upon wave propagation simulations in 3-D earth models using a Spectral Element Method. Comparison between phase delays caused by 3-D wave speed structures and those caused by 3-D Q variations show that anelastic dispersion due to lateral perturbation in Q is important in long-period surface wave and can account for 15-20% observed phase delays. For amplitude perturbations, elastic focusing/defocusing effects associated with 3-D wave speed structures are dominant while energy dissipation is important in short-period (â ¼ 50 s) surface waves but decreases quickly with increasing wave period. Anelastic focusing/defocusing associated with 3-D anelastic dispersion becomes more important than wave attenuation in longer period surface waves. In tomography studies, ray theory breaks down and finite frequency effects become important when the length scale of heterogenities are smaller than seismic wavelength. Finite frequency effects in 3-D earth models are investigated by comparing theoretical predictions of travel times and amplitudes with â ground truthâ measurements made on synthetic seismograms generated in SEM simulations. The comparisons show that finite frequency effects are stronger in amplitudes than in phases, especially at long periods.
Ph. D.

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Zaccherini, Rachele. "Surface waves attenuation in granular media through a small-scale Metabarrier." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.

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The present thesis describes a small-scale experiment, carried out in the laboratory of the Swiss Federal Institute of Technology of Zurich (ETH). The research focuses on metamaterials, locally resonant structures able to affect the propagation of waves passing through them. The present thesis investigates an innovative method to attenuate Rayleigh waves through the insertion of a barrier of scaled resonators into the soil, capable of generating a bandgap in the dispersion relation. Waves, whose frequency fall within the bandgap, cannot propagate through the resonant structure. Each resonator is constituted by a steel mass mounted on top of a spring made with 16 beams forming a truss. Taking advantage of the results of A. Palermo et al [1] as a starting point, we carried out a small-scale experiment in a big wooden box filled with glass beads in order to investigate the effectiveness of the designed metabarrier in attenuating surface waves generated by a metal rod exciting the surface every 300 ms. We found a stop-band in the dispersion relation inside the metabarrier, generated by the coupling between the vertical component of Rayleigh waves and the longitudinal resonances of the resonators. In parallel with the laboratory experiment, some numerical simulations have been performed with the software Comsol Multiphysics in order to compare the results obtained experimentally.

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Waszek, Lauren Esme. "A body wave study of the seismic velocity and attenuation structures of Earth's inner core." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610770.

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Zhang, Yang Ph D. Massachusetts Institute of Technology Dept of Earth Atmospheric and Planetary Sciences. "Modeling of the effects of wave-induced fluid motion on seismic velocity and attenuation in porous rocks." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62322.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.
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 (p. 169-181).
In this thesis, we use the X-ray CT images of Berea sandstones to carry out the numerical study of the effects of wave-induced fluid motion on seismic velocity and attenuation in porous rocks. In numerical modeling, it is possible to control the factors and inputs that are hard to accomplish in laboratory measurements and isolate those of interest that have significant impact on the seismic responses; this can help in understanding the fundamental physics of seismic waves propagating in saturated porous rocks. The ultimate goal of computational rock physics is to supplement the traditional laboratory measurements, that are time consuming and costly, with cheaper numerical experiments that allow the parameter space to be explored more thoroughly. For this purpose, in this thesis we develop a computational method for time domain simulation of wave propagation in poroelastic medium. The medium is composed of an elastic matrix saturated with a Newtonian fluid. The method operates on a digitized representation of the medium where a distinct material phase and properties are specified at each volume cell. The dynamic response to an acoustic excitation is modeled mathematically with a coupled system of equations: elastic wave equation in the solid matrix and linearized Navier-Stokes equation in the fluid. Implementation of the solution is simplified by introducing a common numerical form for both solid and fluid cells and using a rotated-staggered-grid finite-difference scheme which allows stable solutions without explicitly handling the fluid-solid boundary conditions. A stability analysis is incorporated and can be used to select gridding and time step size as a function of material properties. The numerical results are shown to agree with the analytical solution for an idealized porous medium of periodically alternating solid and fluid layers. When applying the linear solver to compute the effective elastic properties of 3D digitized porous rocks, we find discrepancies between the numerical results and the laboratory measurements. The reason for such a problem is the loss of small features, such as cracks and micro-pores, in the digitized matrix of rocks during the imaging process of aggregation. A hybrid approach, combining the numerical computation 3 and the effective media theories, is developed to deduce the lost cracks from a limited number of laboratory measurements. This approach can recover the lost cracks and is capable of predicting the effective elastic properties of the rock matrix. Compared to the traditional inversion schemes based only on the effective media theories, this hybrid scheme has the advantage of utilizing the complex micro-structures of 3D digitized porous rocks that are resolved in the imaging process, and it helps limit the inversion space for crack distribution. In the study of the dynamic and low-frequency responses of saturated porous rocks, we employ the stress-strain calculation in numerical modeling so as to compute the velocities and attenuations of rock samples, the sizes of which are much smaller than the seismic wavelength of interest. For these cases, transmission measurement cannot be used. Realizing the significant contribution of small cracks to the total attenuation, we extend the hybrid approach by incorporating the modified squirt-flow model where a fluid with frequency-dependent bulk modulus is introduced. Therefore, attenuation due to viscous fluid in stiff pores, that are resolved in the imaging process, can be computed numerically. Attenuation due to viscous fluid in compliant pores can be determined by the modified squirt-flow model since we know the crack distribution. In the inversion for crack distribution, besides using the velocities of P- and S-waves measured in laboratory for the dry and water-saturated cases, measured attenuation data of P-waves are also used so as to further constrain the inversion, and to improve the uniqueness of the inversion results. By using such an extended hybrid approach, we are able to predict both the velocities of saturated porous rocks and the attenuations. From numerical study with the linear solver, we can conclude that the linear solver is able to accurately couple elastic solid and viscous fluid and handle high material contrast and the complex micro-structures of 3D digitized porous rocks. The stress-strain calculation is capable of computing the velocities and attenuations of saturated porous rocks the sizes of which are much smaller than the wavelength of interest. The hybrid approach is a practical way to study the seismic properties of saturated porous rocks until high enough resolution digitized data and enough computational resources are available. From the computations, we observe that the small features, such as cracks lost in the imaging process, are critical for accurately predicting velocities and attenuations of saturated porous rocks. Generally, attenuation is more sensitive to the viscosity of the saturating fluid than velocity is, and attenuation due to viscous fluid in compliant pores is greater than that due to viscous fluid in stiff pores.
by Yang Zhang.
Ph.D.

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Brajanovski, Miroslav. "Effects of fractures on seismic waves in poroelastic formations." Curtin University of Technology, Department of Exploration Geophysics, 2004. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=15309.

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Naturally fractured reservoirs have attracted an increased interest of exploration and production geophysics in recent years. In many instances, natural fractures control the permeability of the reservoir, and hence the ability to find and characterize fractured areas of the reservoir represents a major challenge for seismic investigations. In fractured and porous reservoirs the fluid affects elastic anisotropy of the rock and also causes significant frequency dependent attenuation and dispersion. In this study we develop a mathematical model for seismic wave attenuation and dispersion in a porous medium in a porous medium with aligned fractured, caused by wave induced fluid flow between pores and fractures. In this work fractures in the porous rock are modelled as very thin and highly porous layers in a porous background. Dry highly porous materials have low elastic moduli; thus dry skeleton of our system contains thin and soft layers, and is described by linear slip theory. The fluid saturated rock with high-porasity layers is described by equations of poroelasticity with periodically varying coefficients. These equations are analyzed using propagator matrix approach commonly used to study effective properties of layered system. This yields a dispersion equation for a periodically layered saturated porous medium taking into account fluid communication between pore spaces of the layers. Taking in this dispersion equation a limit of small thickness for high-porosity layers gives the velocity and attenuation as a function of frequency and fracture parameters. The results of this analysis show that porous saturated rock with aligned fractures exhibits significant attenuation and velocity dispersion due to wave induced fluid flow between pores and fractures.
At low frequencies the material properties are equal to those obtained by anisotropic Gassmann theory applied to a porous material with linear-slip, interfaces. At high frequencies the results are equivalent to those for fractures with vanishingly small normal slip in a solid (non-porous) background. The characteristic frequency of the attenuation and dispersion depends on the background permeability, fluid viscosity, as well as fracture density and spacing. The wave induced fluid flow between pores and fractures considered in this work has exactly the same physical nature as so-called squirt flow, which is widely believed to by a major cause of seismic attenuation. Hence, the present model can be viewed as a new model of squirt-flow attenuation, consistent with Biot’s theory of poroelasticity. The theoretical results of this work are also limited by the assumption of periodic distribution of fractures. In reality fractures may be distributed in a random fashion. Sensitivity of our results to the violation of the periodicity assumption was examined numerically using reflectivity modelling for layered poroelastic media. Numerical experiments for a random distribution of fractures of the same thickness still show surprisingly good agreement with theoretical results obtained for periodic fractures. However this agreement may break down if fracture properties are allowed to vary from fracture to fracture. The results of this thesis show how to compute frequency dependences of attenuation and velocity caused by wave induced fluid flow between pores and fractures. These results can be used to obtain important parameters of fractured reservoirs, such as permeability and fracture weakness, from attenuation measurements. The major requirement for the success of such an approach is that measurements must be made in over a relatively broad frequency range.

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Durand, Stéphanie. "L'atténuation sismique dans le manteau terrestre." Thesis, Lyon, École normale supérieure, 2012. http://www.theses.fr/2012ENSL0754.

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Cette thèse s’intéresse à divers aspects de l’atténuation sismique dans le manteau terrestre et aux implications de celle-ci quant à la structure de ce dernier. L’enjeu est de mieux comprendre les mécanismes d’atténuation ainsi que les mesures que l’on peut effectuer afin d’améliorer les modèles radiaux d’atténuation dont on dispose et in fine l’interprétation des modèles de tomographie. Je me suis concentrée sur deux exemples de mécanismes d’atténuation, appartenant à deux grands types d’atténuation : l’atténuation intrinsèque, liée à l’absorption par le milieu d’une partie de l’énergie sismique dissipée irréversiblement sous forme de chaleur, et l’atténuation extrinsèque, liée à la dispersion de cette énergie par le milieu. Dans le premier cas, j'ai regardé l’effet des transitions de phase sur l’atténuation des ondes sismiques. En appliquant un modèle thermomécanique développé par Ricard et al., 2009, pour prédire l’atténuation des ondes sismiques liée à la transition de phase uniquement et en comparant les valeurs obtenues aux mesures dont on dispose, j'ai pu contraindre la cinétique d’une transition de phase mantellique. Dans le second cas, j'ai testé l’effet de l’anisotropie comme mécanisme d'atténuation apparente, le but étant de trouver une distribution statistique d’orientation d’anisotropie pouvant reproduire la quasi-constance du facteur de qualité Q avec la fréquence, observée en sismologie et lors d’expériences de laboratoire (Knopoff, 1964), et aujourd’hui expliquée par un modèle ad-hoc seulement (Liu, 1976).Enfin, je me intéressée à mesurer cette atténuation sismique sur des enregistrements réels. Après avoir testé la méthode dite de la fréquence instantanée (Ford et al., 2012), je me suis concentrée sur deux régions, l’Amérique centrale et l’Alaska pour l'appliquer. Ces mesures sont ensuite interprétées en termes de modèle radial d’atténuation révélant un manteau inférieur hétérogène atténuant. Je montre aussi qu’une origine compositionnelle est la plus probable pour expliquer ces anomalies d’atténuation
This thesis is devoted to various aspects of seismic attenuation in the Earth's mantle and the consequences on the mantle structure. The challenge is to better understand the attenuation mechanisms, as well as the measurements that can be done, in order to improve the published radial profiles of attenuation and in fine the interpretation of tomographic models.I focus on two examples of attenuation mechanisms, belonging to two kinds of attenuation: the intrinsic attenuation related to the absorption by the medium of a part of the seismic energy then irreversibly dissipated as heat, and the extrinsic attenuation related to the dispersion of the seismic energy by the medium. In the first case, I investigate the effect of phase transitions upon seismic attenuation. Applying the thermo-mechanical model developped by Ricard et al., 2012, to calculate the attenuation of seismic waves due to the phase transition only and comparing the obtained values to published measurements, I succeed in constraining the kinetics of a mantle phase transition. In the second case, I test the seismic anisotropy as a mechanism of extrinsic attenuation, the aim being to find a statistical distribution of anisotropy orientation and layer thicknesses that can reproduce the observed quasi-frequency independence of Q in seismology and laboratory experiments (Knopoff, 1964), and which is, today, only explained by an ad-hoc model (Liu, 1976).Finally, I was interested in measuring the seismic attenuation on real seismograms. After having tested the method of the instantaneous frequency (Ford et al., 2012), I applied it to seismic records sampling the mantle below Central America and Alaska. These measurements are then inverted for a radial profile of shear attenuation which reveals the existence of an attenuating zone in the lower mantle. I also show that these attenuation anomalies are likely to be of chemical origin

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Solymosi, Bence. "A two-way approach to adapt small-scale laboratory experiments and corresponding numerical simulations of offshore seismic surveys." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0630.

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Les méthodes numériques sont largement utilisées en exploration sismique pour simuler la propagation des ondes et pour le post-traitement des données sismiques avant l'interprétation géologique/géophysique. Les algorithmes sont basés sur différentes hypothèses pour réduire le coût de calcul au détriment de la simplification des modèles et/ou des phénomènes physiques. En raison de leur rôle essentiel en exploration géophysique, la précision des simulations numériques présente un fort intérêt, notamment dans le cas de configurations géologiques réalistes. La comparaison directe des résultats numériques entre eux dans des configurations synthétiques peut avoir des limites, car il peut être difficile de déterminer celui qui donne la meilleure approximation de la solution physique inconnue. Comme dans la réalité le sous-sol n'est jamais connu avec précision, il est également difficile de comparer les résultats synthétiques aux données sismiques réelles acquises in situ. Par conséquent, il y a un grand intérêt à utiliser des mesures de laboratoire sur des modèles physiques aux propriétés connues pour valider la précision des outils numériques. Avant de pouvoir comparer avec précision les mesures et les simulations, nous devons tout d’abord établir un cadre comparatif avec une approche conjointe adaptée aux expériences de laboratoire et à la modélisation numérique. C’est précisément l'objectif de cette thèse. Ainsi, le cadre reproduit d'abord les mesures sismiques marines dans des conditions de laboratoire en utilisant de modèles à échelle réduite, puis les outils numériques sont adaptés à la reconstruction précise des expériences
Numerical methods are widely used in seismic exploration to simulate wave propagation and to post-process the recorded seismic data before the geologic/geophysical interpretation. The algorithms are based on various assumptions to reduce the computational cost at the expense of simplifying the models and/or the physical phenomena. Because of their essential role in exploration geophysics, the accuracy of the numerical simulations is of particular interest, especially in the case of realistic geologic setups. The direct comparison of the numerical results with each other in synthetic configurations can have limitations, as it can be difficult to determine the one that gives the best approximation of a physically unknown solution. Because in real life the subsurface is never accurately known, it is also difficult to compare the synthetic results to any seismic data set from field measurements. Therefore there is a strong interest in using laboratory measurements on physical models of known geometries to benchmark the numerical tools. Before comparing measurements and simulations with confidence at high accuracy, we first need to establish a comparative framework with a jointly-adapted approach to both the laboratory experiments and the numerical modeling. This challenging task is the goal of this thesis. Thus, the framework first reproduces offshore seismic measurements in laboratory conditions with the help of small-scale models, and then the numerical tools are adapted to the accurate synthetic reconstruction of the experiments

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Johnson, Stuart G. "Applications of global seismic tomography and analysis of variational methods for the solution of the linearly attenuating frequency domain wave equation /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823696.

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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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Zaske, Jörg Helmut. "Identification and attenuation of multiple reflections using wavefront characteristics /." [Karlsruhe] : Die Universität, 2000. http://www.ubka.uni-karlsruhe.de/cgi-bin/psgunzip/2000/physik/1/1.pdf.

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Thesis (Doctoral)--Universität Karlsruhe, 2000.
Abstract in German. Includes bibliographical references (p. 107-111). Also available via the World Wide Web. Also available via the World Wide Web. http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=2000/physik/1 http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=/2000/physik/2

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Gagnepain-Beyneix, Jeannine. "Etude experimentale des tremblements de terre : exemple de la region d'arette (france)." Paris 7, 1987. http://www.theses.fr/1987PA077010.

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La localisation des seismes enregistres permet de mettre en evidence une fracture crustale majeure, situee a la bordure nord de la haute chaine et qui pourrait correspondre a la suture des plaques europe et iberie. L'etude des mecanismes au foyer et les resultats de la geodesie montrent une elevation de la haute chaine par rapport a l'avant pays nord. L'examen des parametres de la source montre l'heterogeneite de l'etat de contrainte a la surface de la faille sismique. L'etude de l'attenuation des ondes sismiques ne revele pas de variation du facteur de qualite du milieu liee a l'activite sismique. Ces resultats permettraient de progresser dans les domaines de la sismogenese et de la prevision sismique dans les regions de sismicite moyenne

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Todoeschuck, John 1955. "Non-linear seismic attenuation in the earth as applied to the free oscillations." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72760.

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Jones, Simon Mark. "The effects of confining pressure, pore-fluid salinity and saturation on the acoustic properties of sandstones." Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321879.

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Modern seismic data acquisition and processing methods now enable scientists to extract information on both the stratigraphy and the physical properties of subsurface rocks. Laboratory acoustic measurementsa llow the physical conditions to be precisely measured and controlled. In the present study, P- and S-wave velocities (Vs, VS) and attenuations (1000/Qp, 1000/Qs) were measured in a range of sandstones using the ultrasonic pulse-echo technique, at effective pressures of 5 MPa to 60 MPa. The measurement accuracy is ±0.3 % for velocity and ±0.1 dB/cm for attenuation using this method. Velocities and quality factors( Q) fall with decreasinge ffectivep ressure,a nd the relationships are described by the empirical equationsV =A+KP-B C71' and Q=A-B e7DP , where P is the effective pressure and A, K, B, and D are the regression coefficients (D=0.115±0.016 and 0.048±0.010 for V and Q, respectively). Velocity and Q can therefore be extrapolated to pressures beyond the experimental range. The Biot, Gassmann, and unrelaxed pore-fluid models of seismic wave propagation in porous media fail to explain the pressure-dependenceo f the velocities. The difference between the experimental and Biot model predictions of the rate of change in P-wave velocity with pore fluid salinity (dVýdM) increases with percentage clay content (C) of the rock at the approximately linear rate of 0.95 m/s/mol. There is no clear relationship for dVs/dM. In clean sandstones there is a close agreement between the experimental results and Biot model predictions for dVP/dM, but the agreement breaks down when C>5%. This suggests that changes in the pore-fluid salinity alter the frame bulk and shear moduli of sandstones. Attenuation is generally independent of pore-fluid salinity. Attenuation and velocity are often strongly dependent on the degree of pore-fluid saturation. A study of nine samples shows that 1000/Qp exhibits a resonance peak at midrange saturations (SW av 30 % to SW = 70 %) in most samples, and 1000/Qs shows similar behaviour in several of these. For porosities greater than 13%, the normalised amplitudes of the peaks in P-wave and bulk attenuation are correlated to porosity; the latter increases at a linear rate of 0.98 per percentage increase in porosity. These data suggest that attenuation reaches a maximum when the gas/water mixture is neither too compressible nor too incompressible. The Biot/squirt (BISQ) theory inadequately models the saturation dependence of 1000/Qp and Vp in a sample at low confining pressure. Vp falls with decreasing saturation between SW =100 % to SW - 50 %; below SW = 50 %, the behaviour of Vp is dependent on the confining pressure. Vs generally increases with decreasing saturation over the entire saturation range in all samples. The unrelaxed pore-fluid model of Mavko and Nolen-Hoeksema (1994) describes the Vp data reasonably well in most samples using low wetting fractions (< 15 %), which indicates that the pore fluid is unrelaxed at both the grain and sample scales. The wetting pore fluid becomes unrelaxed at high frequencies and/or low permeabilities. The V. data are poorly described by the model, possibly due to matrix softening by the wetting fluid. The experimental data have indicated significant shortcomings in the mathematical models of seismic wave propagation in reservoir rocks. The data highlight important aspects of wave propagation that must be addressed in revised theories.

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Sidler, Rolf. "Reflection of seismic waves from attenuating and anisotropic ocean bottom sediments /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17891.

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Oliveira, Nisar Rocha de. "Supress?o do ru?do de rolamento superficial utilizando a transformada Curvelet." Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12906.

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Among the many types of noise observed in seismic land acquisition there is one produced by surface waves called Ground Roll that is a particular type of Rayleigh wave which characteristics are high amplitude, low frequency and low velocity (generating a cone with high dip). Ground roll contaminates the relevant signals and can mask the relevant information, carried by waves scattered in deeper regions of the geological layers. In this thesis, we will present a method that attenuates the ground roll. The technique consists in to decompose the seismogram in a basis of curvelet functions that are localized in time, in frequency, and also, incorporate an angular orientation. These characteristics allow to construct a curvelet filter that takes in consideration the localization of denoise in scales, times and angles in the seismogram. The method was tested with real data and the results were very good
Dentre os diversos tipos de ru?dos existentes nos dados s?smicos terrestres est? o Ru?do de Rolamento Superficial tamb?m conhecido como ground roll que ? um tipo particular de ondas de Rayleigh com amplitude forte, freq??ncia baixa e velocidade baixa que gera um cone de grande mergulho no sismograma. O ru?do de rolamento superficial contamina os sinais relevantes e pode mascarar a informa??o desejada, trazidas por ondas espalhadas em regi?es mais profundas das camadas geol?gicas. Nesta disserta??o ser? apresentada uma ferramenta que atenua o ru?do de rolamento superficial baseada na transformada curvelet. A t?cnica consiste em decompor o sismograma em uma base de fun??es curvelets as quais s?o localizadas no tempo e na freq??ncia, al?m de incorporarem uma orienta??o angular. Tais caracter?sticas permitem a constru??o de um filtro curvelet que leva em considera??o a localiza??o do ru?do em escalas, limiares de corte dos coeficientes curvelets e dos ?ngulos no sismograma. O m?todo foi testado com dados reais e os resultados obtidos foram muito bons

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Cabas, Mijares Ashly Margot. "Improvements to the Assessment of Site-Specific Seismic Hazards." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/82352.

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The understanding of the impact of site effects on ground motions is crucial for improving the assessment of seismic hazards. Site response analyses (SRA) can numerically accommodate the mechanics behind the wave propagation phenomena near the surface as well as the variability associated with the input motion and soil properties. As a result, SRA constitute a key component of the assessment of site-specific seismic hazards within the probabilistic seismic hazard analysis framework. This work focuses on limitations in SRA, namely, the definition of the elastic half-space (EHS) boundary condition, the selection of input ground motions so that they are compatible with the assumed EHS properties, and the proper consideration of near-surface attenuation effects. Input motions are commonly selected based on similarities between the shear wave velocity (Vs) at the recording station and the materials below the reference depth at the study site (among other aspects such as the intensity of the expected ground motion, distance to rupture, type of source, etc.). This traditional approach disregards the influence of the attenuation in the shallow crust and the degree to which it can alter the estimates of site response. A Vs-κ correction framework for input motions is proposed to render them compatible with the properties of the assumed EHS at the site. An ideal EHS must satisfy the conditions of linearity and homogeneity. It is usually defined at a horizon where no strong impedance contrast will be found below that depth (typically the top of bedrock). However, engineers face challenges when dealing with sites where this strong impedance contrast takes place far beyond the depth of typical Vs measurements. Case studies are presented to illustrate potential issues associated with the selection of the EHS boundary in SRA. Additionally, the relationship between damping values as considered in geotechnical laboratory-based models, and as implied by seismological attenuation parameters measured using ground motions recorded in the field is investigated to propose alternative damping models that can match more closely the attenuation of seismic waves in the field.
Ph. D.

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Noriega, Salmón Raquel. "Seismic Attenuation Analysis using Lg waves and Ambient Noise Recordings: Application to the Iberian Peninsula and Morocco." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400704.

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In this thesis I have carried out a comprehensive study of the attenuation properties of the Earth´s crust of the Iberia-Morocco region (IMR). I have investigated the crustal attenuation by means of the quality factor Q, which is inversely proportional to attenuation, using both earthquakes and noise-derived measurements. In order to fulfill the thesis objectives a large dataset including earthquake waveforms and seismic noise records has been used. Three different traditional earthquake methods have been implemented to estimate Q in the IMR: the two-station (TS) method, the coda normalization (CN) method and the spectral amplitude decay (SAD) method. For the estimation of Q, these approaches measure the spectral amplitude of the Lg wave (direct and coda) of regional events. Among all the methods evaluated, the TS method allows imaging the spatial variation of the Lg wave attenuation in the Iberian Peninsula whereas the CN and the SAD methods only estimate average attenuation values as well as its frequency dependence. For the Iberian Peninsula, high Lg Q values are observed in the stable Iberian Massif in western Iberia, while lower values are mainly found in the Pyrenean Range and in eastern and southern Iberia. For Morocco, the CN and the SAD methods produce similar results, indicating that the Lg Q models are robust to differences in the methodologies. The frequency-dependent Q estimates represent an average attenuation across a broad region of different structural domains and correlate well with areas of moderate seismicity. Additionally, I have studied the Lg propagation efficiency across the IMR. Results reflect an inefficient or even blocked propagation across the Gulf of Cádiz and for most paths crossing the western Alboran basin. The continental crust of the Iberian Peninsula and Morocco shows efficient Lg propagation. I have also investigated the potential of using ambient noise measurements to retrieve information about the anelastic structure of the Earth´s crust. Since noise preprocessing techniques modify the amplitude of the recovered empirical Green function of the medium, additional tests have to be done in order to verify the reliability of the attenuation results obtained. In this regard, I have carefully examined the influence of the distribution of noise sources and receivers on Q estimates. Azimuthally and spatially averaged Q values derived from noise recordings were further compared with earthquake attenuation measurements. Results reveal that the average Q estimates are in concordance with previous long-period surface-wave measurements from earthquakes in the central part of the Iberian Peninsula. Accurate Q estimates are also found in Morocco. I would like to emphasize that this thesis presents new contributions and improvements to the knowledge of the attenuation structure of the IMR. The first regional map that images the lateral variation of the Lg Q has been estimated for the Iberian Peninsula improving the spatial resolution of earlier studies. The frequency dependence of Lg Q has been also calculated for the first time in Morocco. Furthermore, this work is the first attempt to recover attenuation information from ambient seismic noise measurements in the study area. This novel technique allows us to investigate the attenuation structure of the Earth without the occurrence of earthquakes. Exploiting ambient seismic wavefields for attenuation studies will be a powerful tool to extract information about the anelastic structure and the geodynamics in areas of very low seismicity in the near future. It should be also noticed that recovering crustal attenuation values is important for many reasons. Attenuation estimates can be used to better quantify the hazard associated with earthquake ground shaking. Attenuation is also a valuable property in exploration seismology. For example, the presence of fluids can significantly attenuate the amplitude of the seismic waves.

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Pearce, Dominic Robert. "The characterisation of rock masses from laboratory and field studies of the velocity and attenuation of seismic waves." Thesis, University of Leeds, 1996. http://etheses.whiterose.ac.uk/2431/.

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This thesis addresses the concept of non-destructive rock mass characterisation using in-situ measurements of the velocity and attenuation of seismic waves. The thesis is divided in to two sections, the first of which considers a comprehensive laboratory study of the phenomena of stress-induced velocity and attenuation anisotropy, whilst the second documents a number of field case studies. In the first section, a review is given of the current experimental evidence and theoretical explanations of the factors that affect the propagation of seismic waves. A description is given of the spectral ratio technique for the laboratory determination of P-wave attenuation in rock core samples. The section concludes with the presentation of the results of an investigation of stress-induced velocity and attenuation anisotropy in intact samples, samples induced to failure, and fractured samples. Experimental results show that in-situ measurements of the change in velocity and attenuation could be used to predict stress change in a homogenous rock mass which contains infrequent, isolated fractures. The prediction would be based on laboratory measurements of stress-induced attenuation anisotropy in intact samples. In the second section, a new variant of seismic tomography called Combined Transmission and Reflection Tomography (CTRT) is fully described. In the chapters following this, a number of field cases are documented to show how the technique can be used to identify geological structure such as general stratigraphy, faults, orebody volumes, and man-made features such as old workings and blast induced fracture zones. The technique is shown to be ideal for surveying inaccessible areas and improving tomograms above those that can be produced by the popular transmission tomography algorithms. A final case study considers the use of seismic measurements in the prediction of rock mass behaviour in the footwall of a mine stope. The simple technique described successfully identified fault zones in two stopes before mining commenced, one of which resulted in the subsequent loss of a stope half way through mineral extraction. In conclusion this thesis comprehensively describes how seismic measurements can be used to characterise a rock mass and lays the foundations for using the same measurements for monitoring and predicting rock mass behaviour in active environments.

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Costa, Filho Carlos Alberto da 1988. "Applications of independent component analysis to the attenuation of multiple reflections in seismic data = Aplicações da análise de componentes independentes à atenuação de reflexões múltiplas em dados sísmicos." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/306138.

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Orientador: Martin Tygel
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação Cientifica
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Resumo: As reflexões de ondas sísmicas na subsuperfície terrestre podem ser colocadas em duas categorias disjuntas: reflexões primárias e múltiplas. Reflexões primárias carregam informações pontuais sobre um refletor específico, enquanto reflexões múltiplas carregam informações sobre interfaces e pontos de reflexão variados. Consequentemente é usual tentar atenuar reflexões múltiplas e trabalhar somente com reflexões primárias. Neste trabalho, a teoria de ondas acústicas é desenvolvida somente a partir da equação da onda. Um resultado que demonstra como a propagação de ondas acústicas pode ser descrita somente com uma única multiplicação por matriz é exposta. Este resultado permite que um algoritmo seja desenvolvido que, em teoria, pode ser usado para remover todas as reflexões múltiplas que refletiram na superfície pelo menos uma vez. Uma implementação prática deste algoritmo é mostrada. Por conseguinte, a teoria de análise de componentes independentes é apresentada. Suas considerações teóricas e práticas são abordadas. Finalmente, ela é usada em conjunção com o método de eliminação de múltiplas de superfície para atenuar múltiplas de quatro dados diferentes. Estes resultados são então analisados e a eficácia do método é avaliada
Abstract: The reflections of seismic waves in the subsurface of the Earth can be placed under two disjoint categories: primary and multiple reflections. Primary reflections carry pointwise information about a specific reflector while multiple reflections carry informations about various interfaces and reflection points. Consequently, it is customary to attempt to attenuate multiple reflections and work solely with primary reflections. In this work, the theory of acoustic waves is developed solely from the wave equation. A result that shows how acoustic wave propagation can be described as a single matrix multiplication is exposed. This result enables one to develop an algorithm that, in theory, can be used to remove all multiple reflections that have reflected on the surface at least once. The practical implementation of this algorithm is shown. Thereafter, the theory of independent component analysis is presented. Its theoretical and practical considerations are addressed. Finally, it is used in conjunction with the surface-related multiple elimination method to attenuate multiples in four different datasets. These results are then analyzed and the efficacy of the method is evaluated
Mestrado
Matematica Aplicada
Mestre em Matemática Aplicada

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Martin, Nicolas Williams. "Are P- and S-wave velocities and attenuations related to permeability?, Ultrasonic seismic data for sandstone samples from the Writing-on-Stone Provincial Park in Alberta." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20838.pdf.

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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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Gunn, D. A. "Electronic instrumentation for the measurement of velocities and attenuations of shear and compressional seismic waves in rocks and soils under in-situ stress conditions." Thesis, University of Manchester, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.690902.

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KELNER, SYLVIE. "Etude de la propagation des ondes sismiques dans les milieux fissurés : atténuation, anisotropie et migration de fluide induite par un séisme." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10284.

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La diffraction des ondes sismiques par des milieux fissures en deux dimensions (2d) est etudiee par une methode d'equations integrales aux frontieres ou les fonctions de green sont calculees par la methode des nombres d'ondes discrets (dwbiem : discrete wavenumber boundary integral equations method). Cette methode semi-analytique est particulierement bien adaptee aux problemes de la propagation des ondes sismiques dans un milieu homogene contenant des fissures vides ou remplies de fluide. Toutes les conversions d'ondes sont modelisees en appliquant la dwbiem. En premier lieu, nous avons etudie, par simulations numeriques, comment des milieux fissures pouvaient etre caracterises sismiquement. Nous avons ainsi pu observer des phenomenes d'attenuation et d'anisotropie, selon que la longueur d'onde du champ d'ondes incident est du meme ordre de grandeur ou qu'elle est plus grande que la longueur des fissures. Nous avons retrouve un resultat deja connu qui concerne l'attenuation des ondes elastiques lorsqu'elles traversent un milieu fissure : l'attenuation est maximale lorsque la longueur d'onde incidente est proche de la longueur des fissures. Par ailleurs, nous avons modelise la couche de granite fissuree du site de garner valley, en californie, en nous basant sur la theorie des milieux homogenes equivalents. Plusieurs modeles de milieux fissures restituent bien le taux d'anisotropie observe a garner valley. Une etude comparative de l'attenuation d'ondes s enregistrees la-bas et d'ondes s synthetiques permet de conclure que l'anisotropie s'explique par la presence de fissures verticales (et non horizontales) mais ne permet pas de privilegier un modele plus qu'un autre. Enfin, nous avons simule numeriquement la reponse hydro-mecanique d'un massif fracture a un seisme. Les deformations des fissures et les variations de pression dues au champ d'ondes rayonne par une faille en glissement permettent de connaitre les zones d'expulsion de fluide.

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Munson, Clifford G. "Crustal seismic wave properties of the Island of Hawaii anisotropy and attenuation /." 1995. http://catalog.hathitrust.org/api/volumes/oclc/33807708.html.

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Ting-YuChien and 簡廷宇. "Layered foundation with band gap effect in application to seismic wave attenuation." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/sscuy5.

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碩士
國立成功大學
土木工程學系
106
Seismic metamaterials have been widely studied in recent years. The concept of seismic metamaterials is to filter the most harmful low-frequency seismic waves within band gap to protect buildings from seismic waves. In distinct to most studies, in which seismic metamaterials are placed outside the protected targets. In this thesis, seismic metamaterials are served as the foundation of structural system. The foundation is a layered medium, consisting of rubber and concrete. Based on the theory of elastodynamics and Bloch’s theorem, we analyze the dispersion relation for the layered foundation. The frequency interval of the band gap is calculated by adjusting material parameters, and finite element method is used to simulate the wave propagation in continuum model, which will provide a verification of the trend of wave attenuation and the prediction of the band gap. Since rubber has a characteristic of damping energy dissipation, we also consider that rubber is viscoelastic. Numerical method based on finite element is adopted the generalized Maxwell model. Finally, we conclude that the energy dissipation mechanism is controlled mostly by band gap rather than damping, and the enhanced response due to resonance outside the band gap can be reduced.

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Kingston, Emily, Chris R. I. Clayton, and Jeffery Priest. "GAS HYDRATE GROWTH MORPHOLOGIES AND THEIR EFFECT ON THE STIFFNESS AND DAMPING OF A HYDRATE BEARING SAND." 2008. http://hdl.handle.net/2429/1738.

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Using a specially constructed Gas Hydrate Resonant Column (GHRC), the University of Southampton explored different methods of hydrate synthesis and measured the properties of the resulting sediments, such as shear wave velocity (Vs), compressional wave velocity (Vp) and their respective attenuation measurements (Qs -1 and Qp -1). Two approaches were considered. The first utilises an excess gas technique, where known water volume in the pore space dictates the quantity of hydrate. The second approach uses a known quantity of methane gas within the water saturated pore space to constrain the volume of hydrate. Results from the two techniques show that hydrates formed in excess gas environments cause stiffening of the sediment structure at low concentrations (3%), whereas, even at high concentrations of hydrate (40%) in excess water environments, only moderate increase in stiffness was observed. Additionally, attenuation results show a peak in damping at approximately 5% hydrate in excess gas tests, whereas in excess water tests, damping continues to increase with increasing hydrate content in the pore space. By considering the results from the two approaches, it becomes apparent that formation method has an influence on the properties of the hydrate bearing sand, and must therefore influence the morphology of the hydrate in the pore space.

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Xu, Liu. "Seismic wave propagation and modelling in poro-elastic media with mesoscopic inhomogeneities." 2009. http://hdl.handle.net/2440/58442.

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Biot's theory when applied to homogeneous media (involving the macroscopic flow mechanism) cannot explain the high level of attenuation observed in natural porous media over the seismic frequency range. However, several successful mesocopic inhomogeneity models have been developed to account for P wave attenuation. In this thesis I further develop the approaches to tackle S wave velocity and attenuation, to simulate transient wave propagation in poroelastic media, and to construct new models for determining the effective parameters of porous media containing mesoscopic inhomogeneities. As an important application of the double-porosity dual-permeability (DPDP) model, I have reformulated the effective Biot model using the total-field variables. This gives rise to new and more general governing equations than the previous approach based on the host phase field variables (which become a special case of the more general treatment). The analytical transient solution and dispersion characteristics for the double-porosity model and also for a poro-viscoacoustic model are derived over the entire frequency range for a homogeneous medium. The comparison between the results of the two models shows that dissipation by local mesoscopic flow of the double porosity model is very hard to fit by a single Zener element over a broad band. I chose the relaxation function to approximate the dispersion behaviour of the double porosity model just around the source centre frequency. It is shown that for most water-filled sandstones having a double porosity structure, wave propagation can be well described by the poro-viscoaoustic model with a single Zener element in the seismic frequency range. The transient solution for heterogeneous double porosity media is obtained by a numerical pseudospectral time splitting technique. This method is extended to 2.5-D poro-viscoelastic media to capture both P and S wave behaviour. I also demonstrate that if the frequency is below several Hz, then a single Kelvin-Voigt element gives an even better result than a single Zener element. I propose a two-phase permeability spherical inclusion model and obtain the dispersion curves of phase velocity and dissipation factor for the composite. I then determine the effective dynamic permeability of porous media with mesoscopic heterogeneities over the whole frequency range. This result is used to check the validity of other measures of effective dynamic permeability, deduced from the effective hydraulic permeability by replacing the permeability of the components with their dynamic values as determined from the Johnson, Koplik and Dashen (JKD) model. I also investigate the scattering of plane transverse waves by a spherical porous inclusion embedded in an infinite poroelastic medium. The vector displacement wave equations of Biot’s theory are solved as an infinite series of vector spherical harmonics for the case of a plane S-wave incidence. Then, the non-self-consistent theory is used to derive the dispersion characteristics of shear wave velocity and attenuation for a porous rock having mesoscopic spherical inclusions which are designed to represent either the patchy saturation model or the double porosity model with dilute concentrations of identical inclusions.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1457632
Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2009

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Horn, Chen Song, and 陳松宏. "Shallow Seismic Waves Attenuation from Direct and Reflected Waves." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/66116726521123858859.

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36

Dubendorff, Bruce H. "Changes in seismic velocity and apparent attenuation due to isotropic and anisotropic scattering : results from physical modeling." Thesis, 1987. http://hdl.handle.net/1957/29422.

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Abstract:

Much work is presently being done concerning small scale heterogeneities in the earth's crust. These heterogeneities range from pores in sedimentary rocks up to fluctuations in the density and seismic constants of the earth's crust with scale lengths of kilometers. The ability to study and quantify these heterogeneities using seismic methods would be a major advance in the earth sciences. Physical modeling has been shown to be a useful technique for investigating various aspects of wave propagation. In this thesis, two physical modeling experiments (one three-dimensional and one two-dimensional) are used to investigate the scattering of seismic waves from small scale heterogeneities and the changes in seismic velocity and apparent attenuation resulting from this scattering. The effects of both isotropic and anisotropic scattering on velocity and apparent attenuation are calculated. These experimental results are compared to theoretical results. The theory used for isotropic scattering for the three-dimensional experiment is a modified version of Wu's single scattering theory, where instead of calculating the scattering for a single scatterer using the Born approximation, the exact results for scattering from a cylindrical shape are used. While the results for compressional waves and both components of shear waves compare reasonably well for small scatterer volume fractions, at larger scatterer volume fractions, where the need for multiple scattering is more likely, the results for all waves do not compare as well. Many theories used to test anisotropic scattering predict changes in velocity rather than changes in apparent attenuation. The velocity changes are used primarily in this work due to geometrical focusing by a seismic lens that biases the amplitudes (and hence the estimates of apparent attenuation) at low frequencies where most theories predict apparent attenuation. Velocities are calculated from the data using travel times and low frequency phase shifts for the compressional waves and for one component of the shear waves measured in this two-dimensional experiment. Theories that are used to predict compressional and shear wave velocities for both isotropic and anisotropic scatterers are based on a fractional volume method (isotropic), two crack methods (isotropic and anisotropic), and a finely layered method (anisotropic). The isotropic experimental results have much larger, non-linear changes in the velocities than do the isotropic theoretical results. The anisotropic experimental results have similar shapes to both theoretical anisotropic methods for compressional waves and to the theoretical anisotropic crack method for shear waves. Attenuation is computed using log spectral ratios and compares as well with the theoretical results as can be expected within the limits set. A method using anisotropic apparent attenuation to help quantify the scatterers is developed for use with field data.
Graduation date: 1987

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Yelisetti, Subbarao. "Seismic structure, gas hydrate, and slumping studies on the Northern Cascadia margin using multiple migration and full waveform inversion of OBS and MCS data." Thesis, 2014. http://hdl.handle.net/1828/5719.

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Abstract:

The primary focus of this thesis is to examine the detailed seismic structure of the northern Cascadia margin, including the Cascadia basin, the deformation front and the continental shelf. The results of this study are contributing towards understanding sediment deformation and tectonics on this margin. They also have important implications for exploration of hydrocarbons (oil and gas) and natural hazards (submarine landslides, earthquakes, tsunamis, and climate change). The first part of this thesis focuses on the role of gas hydrate in slope failure observed from multibeam bathymetry data on a frontal ridge near the deformation front off Vancouver Island margin using active-source ocean bottom seismometer (OBS) data collected in 2010. Volume estimates (∼ 0.33 km^3) of the slides observed on this margin indicate that these are capable of generating large (∼ 1 − 2 m) tsunamis. Velocity models from travel time inversion of wide angle reflections and refractions recorded on OBSs and vertical incidence single channel seismic (SCS) data were used to estimate gas hydrate concentrations using effective medium modeling. Results indicate a shallow high velocity hydrate layer with a velocity of 2.0 − 2.1 km/s that corresponds to a hydrate concentration of 40% at a depth of 100 m, and a bottom simulating reflector (BSR) at a depth of 265 − 275 m beneath the seafloor (mbsf). These are comparable to drilling results on an adjacent frontal ridge. Margin perpendicular normal faults that extend down to BSR depth were also observed on SCS and bathymetric data, two of which coincide with the sidewalls of the slump indicating that the lateral extent of the slump is controlled by these faults. Analysis of bathymetric data indicates, for the first time, that the glide plane occurs at the same depth as the shallow high velocity layer (100±10 mbsf). In contrast, the glide plane coincides with the depth of the BSR on an adjacent frontal ridge. In either case, our results suggest that the contrast in sediments strengthened by hydrates and overlying or underlying sediments where there is no hydrate is what causing the slope failure on this margin. The second part of this dissertation focuses on obtaining the detailed structure of the Cascadia basin and frontal ridge region using mirror imaging of few widely spaced OBS data. Using only a small airgun source (120 cu. in.), our results indicate structures that were previously not observed on the northern Cascadia margin. Specifically, OBS migration results show dual-vergence structure, which could be related to horizontal compression associated with subduction and low basal shear stress resulting from over-pressure. Understanding the physical and mechanical properties of the basal layer has important implications for understanding earthquakes on this margin. The OBS migrated image also clearly shows the continuity of reflectors which enabled the identification of thrust faults, and also shows the top of the igneous oceanic crust at 5−6 km beneath the seafloor, which were not possible to identify in single-channel and low-fold multi-channel seismic (MCS) data. The last part of this thesis focuses on obtaining detailed seismic structure of the Vancouver Island continental shelf from MCS data using frequency domain viscoacoustic full waveform inversion, which is first of its kind on this margin. Anelastic velocity and attenuation models, derived in this study to subseafloor depths of ∼ 2 km, are useful in understanding the deformation within the Tofino basin sediments, the nature of basement structures and their relationship with underlying accreted terranes such as the Crescent and the Pacific Rim terranes. Specifically, our results indicate a low-velocity zone (LVZ) with a contrast of 200 m/s within the Tofino basin sediment section at a depth 600 − 1000 mbsf over a lateral distance of 10 km. This LVZ is associated with high attenuation values (0.015 − 0.02) and could be a result of over pressured sediments or lithology changes associated with a high porosity layer in this potential hydrocarbon environment. Shallow high velocities of 4 − 5 km/s are observed in the mid-shelf region at depths > 1.5 km, which is interpreted as the shallowest occurrence of the Eocene volcanic Crescent terrane. The sediment velocities sharply increase about 10 km west of Vancouver Island, which probably corresponds to the underlying transition to the Mesozoic marine sedimentary Pacific Rim terrane. High attenuation values of 0.03 − 0.06 are observed at depths > 1 km, which probably corresponds to increased clay content and the presence of mineralized fluids.
Graduate
0373
0372
0605
subbarao@uvic.ca

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