This thesis work is directed at estimating gas hydrate and free gas distribution and saturation in local structures in the Ulleung Basin, East Sea offshore Korea. The estimates are obtained from a 2-D multi-channel seismic (MCS) reflection profile from the basin. Firstly, structures of locally focused upwelling fluid and gas flow were imaged using time-migrated sections and seismic attributes, and secondly seismic velocities were obtained to estimate gas hydrate and free gas saturations. The structures investigated are up to 1 km across, and are characterized by reduced reflectivity (‘blank zones’) and pulled-up sediment reflectors on the seismic sections. Throughout the study, a comparison is made between the blank zones and areas outside them where not much gas hydrate or gas is expected, to examine their peculiar characteristics as related to the formation of gas hydrate and underlying free gas. The regional depth of possible occurrence of gas hydrate and free gas is determined by predicting the base of the gas hydrate stability zone (BGHSZ) from sediment properties and heat flow estimates calibrated by a few bottom-simulating reflectors (BSRs) from outside the analyzed seismic section. A large number of normal moveout (stacking) velocity profiles were obtained within and outside the blank zones. Interval velocities were then derived by applying the commonly used unconstrained Dix equation as well as by applying constraints to inversion using regularized linear inversion and non-linear Bayesian inversion. The latter method fully explores the uncertainty of the interval velocity estimates. Compared to areas outside the blank zones, the velocities within the blank zones are up to 30% larger at about 30 m above the BGHSZ and up to 65% smaller immediately below the BGHSZ. The velocity increase implies a gas hydrate saturation of 10-40% of the pore space. The velocity decrease implies a free gas saturation of 1-4% of the pore space. Their detailed distribution within individual structures cannot be resolved. Reflector pull-up in time sections in the hydrate zone allows an independent velocity estimate, assuming the pull-up is solely a velocity effect. The implied velocity is much higher than the interval velocity estimates, so there also must be physical deformation. The heat flow estimated depth of the BGHSZ is in good agreement with the transition from gas hydrate to free gas as inferred from seismic velocities. The general conclusion of the thesis work is that a variety of careful analyses of MCS data that characterize the seismic signal and estimate the seismic velocity structure can provide insight into gas hydrate and free gas occurrences. The large amounts of gas hydrate and free gas associated with the blank zones inferred by this study should draw special attention to future energy and climate effects in this area and other similar regions.

Made available in DSpace on 2015-03-13T17:50:33Z (GMT). No. of bitstreams: 1 RosanaMN_DISSERT.pdf: 3523232 bytes, checksum: 011fb01612f8bf7e79dd72d9c0642aae (MD5) Previous issue date: 2010-08-03 / The Borborema Province, Northeastern Brazil, had its internal structure investigated by different geophysical methods like gravity, magnetics and seismics. Additionally, many geological studies were also carried out to define the structural domains of this province. Despite the plethora of studies, there are still many important open aspects about its evolution. Here, we study the velocity structure of S-wave in the crust using dispersion of surface waves. The dispersion of surface waves allows an estimate of the average thickness of the crust across the region between the stations. The inversion of the velocity structure was carried out using the inter-station dispersion of surface waves of Rayleigh and Love types. The teleseismic events are mainly from the edges of the South and North American plates. The period of data collection occurred between 2007 and 2010 and we selected 7 events with magnitude above 5.0 MW and up to 40 km depth. The difference between the events back-azimuths and the interstation path was not greater than 10. We also know the depth of the Moho, results from Receiver Functions (Novo Barbosa, 2008), and use those as constrains in inversion. Even using different parameterizations of models for the inversion, our results were very similar the mean profiles velocity structure of S-wave. In pairs of stations located in the Cear?a Central Domain Borborema the province, there are ranges of depths for which the velocities of S are very close. Most of the results in the profile near the Moho complicate their interpretation at that depth, coinciding with the geology of the region, where there are many shear zones. In particular, the profile that have the route Potiguar Bacia in inter-station, had low velocities in the crust. We combine these results to the results of gravimetry and magnetometry (Oliveira, 2008) and receptor function (Novo Barbosa, 2008). We finally, the first results on the behavior of the velocity structure of S-wave with depth in the Province Borborema / A Prov?ncia Borborema, Nordeste do Brasil, tem sua estrutura interna investigada por diferentes m?todos geof?sicos: gravim?tricos, magn?ticos e s?smicos. Adicionalmente, muitos estudos geol?gicos foram levados a definir dom?nios estruturais para a prov?ncia; mas, ainda h? muitos aspectos em aberto sobre sua evolu??o. Neste trabalho, estudamos o comportamento da velocidade da onda S com a profundidade na crosta, usando a caracter?stica de dispers?o das ondas de superf?cie. No m?todo Inter-Esta??o, a dispers?o calculada em cada esta??o, nos ajuda a estimar a espessura m?dia da crosta na regi?o entre as duas esta??es. As invers?es das curvas de dispers~ao s~ao feitas usando a dispers?o inter-esta??o de ondas Rayleigh e Love. Os eventos teless??smicos selecionados s?o principalmente das bordas das placas Sul-Americana e Americana. O per?odo da coleta de dados ocorreu entre 2007 e 2010. Foram usados 7 eventos com magnitudes acima de 5.0 MW e at? 40 km de profundidade. A pequena quantidade de dados se justifica pelo fato dos eventos estarem a pelo menos 10_ do caminho de c?rculo m?ximo entre as esta?oes. Usamos tamb?em o conhecimento da profundidade da Moho, resultados de Fun??es do Receptor (Novo Barbosa, 2008) como v??nculos na invers?o. Mesmo usando diferentes parametriza??es de modelos para a invers~ao, nossos resultados foram de perfis m?edios de velocidade de onda S muito parecidos. Nos pares de estac? ~oes localizados no dom??nio Cear? Central da Prov??ncia Borborema, h? intervalos de profundidades, para os quais as velocidades de S s?o muito pr?ximas na regi?o inter-estac? ~ao desse dom??nio. Na maioria dos resultados, as varia??es da velocidade da onda S no perfil pr?oximas a Moho, dificultam a interpreta??o dos mesmos a essa profundidade e podem indicar forte varia??o lateral, coincidindo com a geologia da regi?o, onde existem muitas zonas de cisalhamento. Em particular, o perfil que possui a Bacia Potiguar no percurso inter-estac? ~ao, apresenta baixas velocidades na crosta. Integramos esses resultados aos resultados da gravimetria e magnetometria (Oliveira, 2008) e func? ~ao do receptor (Novo Barbosa, 2008). Assim, obtivemos os primeiros ind??cios sobre o comportamento da velocidade da onda S com a profundidade, na prov??ncia Borborema

As one of the most common minerals in crustal rocks, quartz has been widely used as an indicator for shock metamorphism. Shocked quartz is found in the Chicxulub impact crater, an impact crater that has been linked to the Cretaceous-Tertiary extinction ~66 million years ago. The microstructural deformation features found in the shocked quartz do not form randomly, and their orientation provides a better understanding of the impact cratering process. At present, there are no studies of EBSD data analysis of shocked quartz from Chicxulub. We investigated six thin sections from two samples from the M0077A borehole in the lower peak ring of the Chicxulub impact crater, using the Scanning Electron Microscopy (SEM)-EBSD technique. Both samples consist of shocked granite, with a significant amount of quartz.  Therefore, this study investigates the crystallographic preferred orientation (CPO) of shocked quartz and predicts the seismic velocities and anisotropy, based on the EBSD data. We carried out the analysis of EBSD data by using the MATLAB-based MTEX toolbox that can perform CPO analysis from pole figure plots and the prediction of seismic properties of minerals based on the Voigt-Reuss-Hill effective medium method. Although acquiring the EBSD data from these samples is challenging, leading to the lack of data measured, we found out that the prediction of P wave seismic velocity is in good agreement with other recent studies conducted in the same area. The range of predicted P wave velocities is 5.5-6.5 km/s with anisotropy of 8-15%. The actual observed laboratory measurements and in-situ seismic measurements are considerably smaller than this velocity range because our calculations do not incorporate pores or take microcracks into account.  A likely explanation for the large variability of anisotropy in shocked quartz is the relatively few mapped grains with EBSD, which would influence the CPO and lead to high predicted seismic anisotropy. Considering a greaternumber of grains in the CPO analysis, the CPO is reduced, and seismic anisotropy becomes smaller.

Mining engineers are tasked with ensuring that underground mining operations be both safe and efficiently productive. Induced stress in deep mines has a significant role in the stability of the underground mines and hence the safety of the mining workplace because the behavior of the rock mass associated with mining-induced seismicity is poorly-understood. Passive seismic tomography is a tool with which the performance of a rock mass can be monitored in a timely manner. Using the tool of passive seismic tomography, the advance rate of operation and mining designs can be updated considering the induced stress level in the abutting rock. Most of our current understanding of rock mass behavior associated with mining-induced seismicity comes from numerical modeling and a limited set of case studies. Therefore, it is critical to continuously monitor the rock mass performance under induced stress. Underground stress changes directly influence the seismic wave velocity of the rock mass, which can be measured by passive seismic tomography. The precise rock mass seismicity can be modeled based on the data recorded by seismic sensors such as geophones of an in-mine microseismic system. The seismic velocity of rock mass, which refers to the propagated P-wave velocity, varies associated with the occurrence of major seismic events (defined as having a local moment magnitude between 2 to 4). Seismic velocity changes in affected areas can be measured before and after a major seismic event in order to determine the highly stressed zones. This study evaluates the seismic velocity trends associated with five major seismic events with moment magnitude of 1.4 at a deep narrow-vein mine in order to recognize reasonable patterns correlated to induced stress redistribution. This pattern may allow recognizing areas and times which are prone to occurrence of a major seismic event and helpful in taking appropriate actions in order to mitigate the risk such as evacuation of the area in abrupt cases and changing the aggressive mine plans in gradual cases. In other words, the high stress zones can be distinguished at their early stage and correspondingly optimizing the mining practices to prevent progression of high stress zones which can be ended to a rock failure. For this purpose a block cave mine was synthetically modeled and numerically analyzed in order to evaluate the capability of the passive seismic tomography in determining the induced stress changes through seismic velocity measurement in block cave mines. Next the same method is used for a narrow vein mine as a case study to determine the velocity patterns corresponding to each major seismic event. / Doctor of Philosophy / Mining activities unbalance the stress distribution underground, which is called mining induced stress. The stability of the underground mines is jeopardized due to accumulation of induced stress thus it is critical for the safety of the miners to prevent excessive induced stress accumulation. Hence it is important to continuously monitor the rock mass performance under the induced stress which can form cracks or slide along the existing discontinuities in rock mass. Cracking or sliding releases energy as the source of the seismic wave propagation in underground rocks, known as a seismic event. The velocity of seismic wave propagation can be recorded and monitored by installing seismic sensors such as geophones underground. The seismic events are similar to earthquakes but on a much smaller scale. The strength of seismic events is measured on a scale of moment magnitude. The strongest earthquakes in the world are around magnitude 9, most destructive earthquakes are magnitude 7 or higher, and earthquakes below magnitude 5 generally do not cause significant damage. The moment magnitude of mining induced seismic events is typically less than 3. In order to monitor mining induced stress variations, the propagated seismic wave velocity in rock mass is measured by a series of mathematical computations on recorded seismic waves called passive seismic tomography, which is similar to the medical CT-scan machine. Seismic wave velocity is like the velocity of the vibrating particles of rock due to the released energy from a seismic event. This study proposes to investigate trends of seismic velocity variations before and after each seismic event. The areas which are highly stressed have higher seismic velocities compared to the average seismic velocity of the entire area. Therefore, early recognition of highly stressed zones, based on the seismic velocity amount prior the occurrence of major seismic events, will be helpful to apply optimization of mining practices to prevent progression of high stress zones which can be ended to rock failures. For this purpose, time-dependent seismic velocity of a synthetic mine was compared to its stress numerically. Then, the seismic data of a narrow vein mine is evaluated to determine the seismic velocity trends prior to the occurrence of at least five major seismic events as the case study.

Overpressure, or abnormally low effective pressures, is hazardous in drilling operations and construction of sea-bottom facilities in deepwater environments. Estimation of the locations of overpressure can improve safety in these operations and significantly reduce overall project costs. Propagation velocities of both seismic P and S wave are sensitive to bulk elastic parameters and density of the sediments, which can be related to porosity, pore fluid content, lithology, and effective pressures. Overpressured areas can be analyzed using 4C seismic reflection data, which includes P-P and P-SV reflections. In this thesis, the effects on compressional (P) and shear (S) wave velocities are investigated to estimate the magnitude and location of excess pore pressure utilizing Eaton’s approach for pressure prediction (Eaton, 1969). Eaton’s (1969) method relates changes in pore pressure to changes in seismic P-wave velocity. The underlying assumption of this method utilizes the ratio of observed P-wave velocity obtained from areas of both normal and abnormal pressure. This velocity ratio evaluated through an empirically determined exponent is then related to the ratio of effective stress under normal and abnormal pressure conditions. Effective stress in a normal pressured condition is greater than the effective stress value in abnormally overpressured conditions. Due to an increased sensitivity of variations in effective pressure to seismic interval velocity, Ebrom et al. (2003) employ a modified Eaton equation to incorporate the S-wave velocity in pore pressure prediction. The data preparation and subsequent observations of seismic P and S wave velocity estimates in this thesis represent a preliminary analysis for pore pressure prediction. Six 2D receiver gathers in the regional dip direction are extracted from six individual ocean-bottom 4C seismic recording nodes for P-P and P-SV velocity analysis. The receiver gathers employed have minimal pre-processing procedures applied. The main processing steps applied were: water bottom mute, 2D rotation of horizontal components to SV and SH orientation, deconvolution, and frequency filtering. Most the processing was performed in Matlab with a volume of scripts designed by research scientists from the University of Texas, Bureau of Economic Geology. In this thesis, fluid pressure prediction is estimated utilizing several 4C multicomponent ocean-bottom nodes in the Atlantis Field in deepwater Gulf of Mexico. Velocity analysis is performed through a ray tracing approach utilizing P-P and P-SV registration. A modified Eaton’s Algorithm is then used for pore pressure prediction using both P and S wave velocity values. I was able to successfully observe both compressional and shear wave velocities to sediment depths of approximately 800 m below the seafloor. Using Hamilton (1972, 1976) and Eberhart-Phillips et al. (1989) regressions as background depth dependent velocity values and well-log derived background effective pressure values from deepwater Gulf of Mexico, I am able to solve for predicted effective pressure for the study area. The results show that the Atlantis subsurface study area experiences a degree of overpressure. / text

Ein transversales Störungssystem im Nahen Osten, die Dead Sea Transform (DST), trennt die Arabische Platte von der Sinai-Mikroplatte und erstreckt sich von Süden nach Norden vom Extensionsgebiet im Roten Meer über das Tote Meer bis zur Taurus-Zagros Kollisionszone. Die sinistrale DST bildete sich im Miozän vor etwa 17 Ma und steht mit dem Aufbrechen des Afro-Arabischen Kontinents in Verbindung. Das Untersuchungsgebiet liegt im Arava Tal zwischen Totem und Rotem Meer, mittig über der Arava Störung (Arava Fault, AF), die hier den Hauptast der DST bildet.<br /> <br /> Eine Reihe seismischer Experimente, aufgebaut aus künstlichen Quellen, linearen Profilen über die Störung und entsprechend entworfenen Empfänger-Arrays, zeigt die Untergrundstruktur in der Umgebung der AF und der Verwerfungszone selbst bis in eine Tiefe von 3-4 km. Ein tomographisch bestimmtes Modell der seismischen Geschwindigkeiten von P-Wellen zeigt einen starken Kontrast nahe der AF mit niedrigeren Geschwindigkeiten auf der westlichen Seite als im Osten. Scherwellen lokaler Erdbeben liefern ein mittleres P-zu-S Geschwindigkeitsverhältnis und es gibt Anzeichen für Änderungen über die Störung hinweg. Hoch aufgelöste tomographische Geschwindigkeitsmodelle bestätigen der Verlauf der AF und stimmen gut mit der Oberflächengeologie überein. <br /> <br /> Modelle des elektrischen Widerstands aus magnetotellurischen Messungen im selben Gebiet zeigen eine leitfähige Schicht westlich der AF, schlecht leitendes Material östlich davon und einen starken Kontrast nahe der AF, die den Fluss von Fluiden von einer Seite zur anderen zu verhindern scheint. Die Korrelation seismischer Geschwindigkeiten und elektrischer Widerstände erlaubt eine Charakterisierung verschiedener Lithologien im Untergrund aus deren physikalischen Eigenschaften. Die westliche Seite lässt sich durch eine geschichtete Struktur beschreiben, wogegen die östliche Seite eher einheitlich erscheint. Die senkrechte Grenze zwischen den westlichen Einheiten und der östlichen scheint gegenüber der Oberflächenausprägung der AF nach Osten verschoben zu sein.<br /> <br /> Eine Modellierung von seismischen Reflexionen an einer Störung deutet an, dass die Grenze zwischen niedrigen und hohen Geschwindigkeiten eher scharf ist, sich aber durch eine raue Oberfläche auf der Längenskala einiger hundert Meter auszeichnen kann, was die Streuung seismischer Wellen begünstigte. Das verwendete Abbildungsverfahren (Migrationsverfahren) für seismische Streukörper basiert auf Array Beamforming und der Kohärenzanalyse P-zu-P gestreuter seismischer Phasen. Eine sorgfältige Bestimmung der Auflösung sichert zuverlässige Abbildungsergebnisse.<br /> <br /> Die niedrigen Geschwindigkeiten im Westen entsprechen der jungen sedimentären Füllung im Arava Tal, und die hohen Geschwindigkeiten stehen mit den dortigen präkambrischen Magmatiten in Verbindung. Eine 7 km lange Zone seismischer Streuung (Reflektor) ist gegenüber der an der Oberfläche sichtbaren AF um 1 km nach Osten verschoben und lässt sich im Tiefenbereich von 1 km bis 4 km abbilden. Dieser Reflektor markiert die Grenze zwischen zwei lithologischen Blöcken, die vermutlich wegen des horizontalen Versatzes entlang der DST nebeneinander zu liegen kamen. Diese Interpretation als lithologische Grenze wird durch die gemeinsame Auswertung der seismischen und magnetotellurischen Modelle gestützt. Die Grenze ist möglicherweise ein Ast der AF, der versetzt gegenüber des heutigen, aktiven Asts verläuft. Der Gesamtversatz der DST könnte räumlich und zeitlich auf diese beiden Äste und möglicherweise auch auf andere Störungen in dem Gebiet verteilt sein. / The Dead Sea Transform (DST) is a prominent shear zone in the Middle East. It separates the Arabian plate from the Sinai microplate and stretches from the Red Sea rift in the south via the Dead Sea to the Taurus-Zagros collision zone in the north. Formed in the Miocene about 17 Ma ago and related to the breakup of the Afro-Arabian continent, the DST accommodates the left-lateral movement between the two plates. The study area is located in the Arava Valley between the Dead Sea and the Red Sea, centered across the Arava Fault (AF), which constitutes the major branch of the transform in this region.<br /> <br /> A set of seismic experiments comprising controlled sources, linear profiles across the fault, and specifically designed receiver arrays reveals the subsurface structure in the vicinity of the AF and of the fault zone itself down to about 3-4 km depth. A tomographically determined seismic P velocity model shows a pronounced velocity contrast near the fault with lower velocities on the western side than east of it. Additionally, S waves from local earthquakes provide an average P-to-S velocity ratio in the study area, and there are indications for a variations across the fault. High-resolution tomographic velocity sections and seismic reflection profiles confirm the surface trace of the AF, and observed features correlate well with fault-related geological observations.<br /> <br /> Coincident electrical resistivity sections from magnetotelluric measurements across the AF show a conductive layer west of the fault, resistive regions east of it, and a marked contrast near the trace of the AF, which seems to act as an impermeable barrier for fluid flow. The correlation of seismic velocities and electrical resistivities lead to a characterisation of subsurface lithologies from their physical properties. Whereas the western side of the fault is characterised by a layered structure, the eastern side is rather uniform. The vertical boundary between the western and the eastern units seems to be offset to the east of the AF surface trace.<br /> <br /> A modelling of fault-zone reflected waves indicates that the boundary between low and high velocities is possibly rather sharp but exhibits a rough surface on the length scale a few hundreds of metres. This gives rise to scattering of seismic waves at this boundary. The imaging (migration) method used is based on array beamforming and coherency analysis of P-to-P scattered seismic phases. Careful assessment of the resolution ensures reliable imaging results.<br /> <br /> The western low velocities correspond to the young sedimentary fill in the Arava Valley, and the high velocities in the east reflect mainly Precambrian igneous rocks. A 7 km long subvertical scattering zone reflector is offset about 1 km east of the AF surface trace and can be imaged from 1 km to about 4 km depth. The reflector marks the boundary between two lithological blocks juxtaposed most probably by displacement along the DST. This interpretation as a lithological boundary is supported by the combined seismic and magnetotelluric analysis. The boundary may be a strand of the AF, which is offset from the current, recently active surface trace. The total slip of the DST may be distributed spatially and in time over these two strands and possibly other faults in the area.

Quantifying the influence of pressure on the effective elastic rock properties is important for applications in rock physics and reservoir characterization. Here I investigate the relationship between effective pressure and seismic velocities by performing inversion on the laboratory-measured data from a suite of clastic, carbonate and igneous rocks, using different analytic and discrete inversion schemes. I explore the utility of a physical model that models a natural fracture as supported by asperities of varying heights, when an effective pressure deforms the tallest asperities, bringing the shorter ones into contact while increasing the overall fracture stiffness. Thus, the model is known as the ?asperity-deformation? (ADM) or ?bed-of-nails? (BNM) model. Existing analytic solutions include one that assumes the host rock is infinitely more rigid than the fractures, and one that takes the host-rock compliance into account. Inversion results indicate that although both solutions can fit the data to within first-order approximation, some systematic misfits exist as a result of using the rigid-host solution, whereas compliant-host inversion returns smaller and random misfits, yet out-of-range parameter estimates. These problems indicate the effects of nonlinear elastic deformation whose degree varies from rock to rock. Consequently, I extend the model to allow for the pressure dependence of the host rock, thereby physically interpreting the nonlinear behaviors of deformation. Furthermore, I apply a discrete grid-search inversion scheme that generalizes the distribution of asperity heights, thus accurately reproduces velocity profiles, significantly improves the fit and helps to visualize the distribution of asperities. I compare the analytic and numerical asperity-deformation models with the existing physical model of elliptical ?pennyshape? cracks with a pore-aspect-ratio (PAR) spectrum in terms of physical meaning and data-fitting ability. The comparison results provide a link and demonstrate the consistency between the use of the two physical models, making a better understanding of the microstructure as well as the contact mechanism and physical behaviors of rocks under pressure. ADM-based solutions, therefore, have the potential to facilitate modeling and interpretation of applications such as time-lapse seismic investigations of fractured reservoirs.

High-frequency wave phenomena is observed in many physical settings, most notably in acoustics, electromagnetics, and elasticity. In all of these fields, numerical simulation and modeling of the forward propagation problem is important to the design and analysis of many systems; a few examples which rely on these computations are the development of metamaterial technologies and geophysical prospecting for natural resources. There are two modes of modeling the forward problem: the frequency domain and the time domain. As the title states, this work is concerned with the former regime. The difficulties of solving the high-frequency wave propagation problem accurately lies in the large number of degrees of freedom required. Conventional wisdom in the computational electromagnetics commmunity suggests that about 10 degrees of freedom per wavelength be used in each coordinate direction to resolve each oscillation. If K is the width of the domain in wavelengths, the number of unknowns N grows at least by O(K^2) for surface discretizations and O(K^3) for volume discretizations in 3D. The memory requirements and asymptotic complexity estimates of direct algorithms such as the multifrontal method are too costly for such problems. Thus, iterative solvers must be used. In this dissertation, I will present fast algorithms which, in conjunction with GMRES, allow the solution of the forward problem in O(N) or O(N log N) time. / text

La composition interne de notre planète est un vaste sujet d’étude auquel participent de nombreuses disciplines scientifiques. Les conditions extrêmes de pression et de température qui règnent à l’intérieur du noyau (constitué principalement de fer et de nickel) et du manteau terrestre (à base de pérovskites) rendent très difficile la détermination de leur compositions exactes. Ce projet de thèse contribue aux études récentes dont l’enjeu est de déterminer plus précisément le chimisme des minéraux présents. Il a pour objet le développement d’un outil de calcul des vitesses de propagation des ondes sismiques a l’aide d’une méthode fondée sur les simulations ab initio. Ces vitesses sont déduites du tenseur élastique complet, incluant la relaxation atomique et les modifications induites du champ cristallin. Nous utilisons l’approche de la théorie de perturbation de la fonctionnelle de la densité (DFPT) qui permet de s'affranchir des incertitudes numériques qu’impliquent les méthodes classiques basées sur des différences finies. Nous combinons cette approche avec le formalisme « Projector Augmented-Wave » (PAW) qui permet, avec un coût de calcul faible, de prendre en compte tous les électrons du système. Nous avons appliqué la méthode sur des matériaux du noyau et du manteau terrestre. Nous avons déterminé les effets de différents éléments légers (Si, S, C, O et H) sur les vitesses de propagation des ondes sismiques dans le fer pur ainsi que celui de l’aluminium dans la pérovskite MgSiO3. / The internal composition of our planet is a large topic of study and involves many scientific disciplines. The extreme conditions of pressure and temperature prevailing inside the core (consisting primarily of iron and nickel) and the mantle (consisting mainly of perovskites) make the determination of the exact compositions very difficult. This thesis contributes to recent studies whose aim is to determine more accurately the chemistry of these minerals. Its purpose is the development of a tool for the calculation of seismic wave velocities within methods based on ab-initio simulations. These velocities are calculated from the full elastic tensor, including the atomic relaxation and induced changes in the crystal field. We use the approach of the density functional perturbation theory (DFPT) to eliminate numerical uncertainties induced by conventional methods based on finite differences. We combine this approach with the « Projector Augmented-Wave » (PAW) formalism that takes into account all the electrons of the system with a low computational cost. We apply the method on core and mantle materials and we determine the effects of various lights elements (Si, S, C, O and H) on the seismic wave velocities of pure iron, as well as the effect of aluminum in the perovskite MgSiO3.