Utilizamos neste trabalho duas metodologias distintas, a função do receptor com ondas P e a função do receptor com ondas S, para mapear variações da crosta e interfaces do manto (litosfera-astenosfera, 410 km e 660 km) em diferentes estações sismográficas na placa Sul-Americana. No estudo da interface litosfera-astenosfera, por ser o primeiro realizado nesta região, utilizamos as estações temporárias do IAG/USP em conjunto com as estações permanentes da rede mundial cobrindo toda a placa Sul-Americana. O estudo para as outras interfaces (Crosta-Manto, 410 km e 660 km) foi feito com caráter regional, buscando detalhar características da crosta e manto na região estável da placa. Para ambos os métodos os traços (sismogramas) foram rotacionados para o sistema LQT, deconvolvidos, agrupados por pontos de perfuração e por estações, e finalmente empilhados. Nos traços empilhados as fases convertidas de interesse (Ps, Ppps, Ppss+Psps e Sp) foram identificadas e interpretadas. Para a parte estável da placa obtivemos um valor médio de espessura da crosta de 39.4±0.6 km, variando desde 31.0±0.5 km para a província Borborema, até 41.3±1.0 km para a bacia do Paraná, onde aplicamos uma correção para descontar o efeito do sedimento. A razão de velocidade para a crosta, Vp/Vs, apresentou valores mais altos para a bacia do Paraná (~1.75±0.08) e região litorânea oriental (>1.74), enquanto que as regiões cratônicas (cráton São Francisco e Amazônico) apresentaram valores de Vp/Vs baixos (<1.72), chegando até 1.68. O valor médio de Vp/Vs para todas as estações analisadas foi de 1.73±0.02. As variações dos tempos para as interfaces do manto mostraram boa correlação com resultados de tomografia sísmica de outros trabalhos, indicando alterações de até 5% na velocidade das ondas sísmicas para o manto superior sob os crátons, uma deflexão de até 15 km na interface de 660 km para a região Sul da bacia do Paraná e se mostraram bem correlacionadas com as médias globais para as outras região estudadas. Por fim, a espessura da litosfera apresentou valores desde ~40 km, sob as regiões de ilhas oceânicas, até ~160 km, sob as regiões mais estáveis. Para as regiões oceânicas a espessura da litosfera se mostra correlacionada com a idade da placa. À medida que adentramos a parte continental, o limite litosfera-astenosfera se torna menos proeminente, atingindo profundidades maiores no interior dos continentes e menores para as regiões marginais. Para a zona de subducção, observamos duas possíveis litosferas, uma oceânica, subduzindo junto com a placa de Nazca, e outra pertencente à parte continental. / Two distinct methodologies, the P- and S-wave receiver functions, are used to map variations in the crustal parameters (thickness and Vp/Vs) and mantle interfaces (lithosphere-asthenosphere, 410 km and 660 km) on a number of different seismograph stations located in the South American plate. The results of the S receiver function for the lithosphere-asthenosphere boundary are the first of this kind ever performed in South American continent and showed the large scale variations of this interface. To perform this study we analyze data from various global permanent stations together with all available data from temporary stations operated by the IAG/USP during the last15 years. For both methods the traces (seismograms) were rotated to the LQT system, deconvolved, grouped by piercing points and stations, and finally stacked. In the stacked traces, the converted phases (Ps, Ppps, Ppss+Psps and Sp) were identified and interpreted. Inside the stable part of the plate we found a mean crustal thickness of 39.4±0.6 km, ranging from 31.0±0.5 km in Borborema Province up to 41.3±1.0 km in the Paraná Basin, where we applied a correction to remove the sediment effects on the crustal estimates. The crustal velocity ratios, Vp/Vs, showed higher values for the Paraná Basin (~1.75±0.08) and Ribeira belt (>1.74), while the cratonic regions (São Francisco and Amazon cratons) showed low values of Vp/Vs (<1.72), down to 1.68. The average Vp/Vs obtained for all stations was equal to 1.73±0.02. The observed times of the converted mantle phases presented a good correlation with other tomographic studies, indicating that the upper mantle for the cratonic roots may be characterized by a variation up to 5% in seismic velocities, a 15 km deflection in the South Paraná 660 km discontinuity (probably due to a decreased temperature caused by the subducted slab); for other regions the converted times were close to the global average. As a final result, the lithospheric thickness presented values ranging from ~40 km under oceanic islands, to ~160 km under the stable continental regions. We found that for the oceanic islands the thickness of the lithosphere is correlated with the age of the plate. When we go further inside the continents, the lithosphere-asthenosphere boundary becomes less sharp, reaching larger depths inside the continents and shallower depths near the continental margin. In the Andean subduction area, we observed two possibles lithospheres, one oceanic, subducting together with the Nazca plate, and another belonging to the Continent, parallel to the crust interface.

Este trabalho consiste no estudo da estrutura sedimentar da Bacia do Paraná da região de Bebedouro utilizando função do receptor, ondas de superfície e sísmica de refração. Funções do Receptor (FR) mostram a resposta da estrutura geológica abaixo de uma estação sismográfica. Para diminuir a não unicidade na inversão do traço de uma FR, foram usadas curvas de dispersão de ondas de superfície como vínculos adicionais. Ondas de superfície foram também obtidas com a correlação cruzada de ruído sísmico ambiental. Esse método passivo permite a obtenção de dispersão em períodos intermediários entre os dados de telessismos e os dados de sísmica rasa auxiliando na determinação estruturas sedimentares. Foi utilizada a inversão conjunta de FR de alta e baixa frequência, dispersão de fase e grupo de períodos menores que 2 s e dispersão de ondas Love e Rayleigh continentais (períodos entre 10 e 100 s). Na inversão conjunta, foram usados vários modelos iniciais diferentes para garantir melhor cobertura do espaço de soluções possíveis. Os resultados mostram uma camada de basalto com uma espessura entre 200 e 400 m, sob uma camada superficial de arenito de 50 a 100m. O embasamento da bacia está torno de 2.5 3.0 km. A espessura e razão Vp/Vs crustal da região foi estimada em 40.0 (1.0) km e 1.78 (0.02). Foi possível identificar zonas de baixa velocidade dentro do pacote de basalto, possivelmente relacionadas a zonas de fraturas ou camadas de basalto alterado. Estas camadas de baixa velocidade estão na parte sul, próximas à área de maior sismicidade induzida e também relativamente mais perto dos poços profundos de maior vazão. Isto corrobora com a hipótese de que a sismicidade local está associada à exploração de poços e estrutura de falhas pré -existentes. / A study of the seismic structure of the Paraná Basin in Bebedouro, SP, was carried out with Receiver Functions (RF). Both low frequency (with ~0.5 Hz low pass filter) and high-frequency (~10Hz) RFs were jointly inverted with surface wave dispersion curves. Surface-wave data included: long-period group velocities of Rayleigh and Love waves from continental-scale tomography in the period range 10-100 s (useful to control crustal scale structure and Moho depth), intermediate period group velocities near 1s period obtained from cross-correlation of ambient noise (useful to control sedimentary structure), phase velocities near 0.2-1.0 s obtained from local earthquakes, and phase velocities of Rayleigh waves from shallow seismic refraction data near ~0.1 s period (useful to control shallow layers). Joint inversion was obtained with several different initial models to better cover all possible solutions. The results indicate that the basalt layer is 200 to 400m thick, beneath sandstones of about 50 100m thick. The Basin basement was detected between 2.5 3.0 km depth, consistent with expected values from regional bore-hole data in the Paraná Basin. Beneath several stations a low-velocity zone was detected in the middle of the basalt pack which is interpreted as a zone of fractured or altered basalt. This anomalous low-velocity layer was detected near the most seismically active zone in the Andes district. It is also relatively close to the deep wells with larger outflow. The existence of this low-velocity zone in the middle of the basalt layer is consistent with the model proposed for the water-well induced seismicity.

Este trabalho consiste no estudo da estrutura sedimentar da Bacia do Paraná da região de Bebedouro utilizando função do receptor, ondas de superfície e sísmica de refração. Funções do Receptor (FR) mostram a resposta da estrutura geológica abaixo de uma estação sismográfica. Para diminuir a não unicidade na inversão do traço de uma FR, foram usadas curvas de dispersão de ondas de superfície como vínculos adicionais. Ondas de superfície foram também obtidas com a correlação cruzada de ruído sísmico ambiental. Esse método passivo permite a obtenção de dispersão em períodos intermediários entre os dados de telessismos e os dados de sísmica rasa auxiliando na determinação estruturas sedimentares. Foi utilizada a inversão conjunta de FR de alta e baixa frequência, dispersão de fase e grupo de períodos menores que 2 s e dispersão de ondas Love e Rayleigh continentais (períodos entre 10 e 100 s). Na inversão conjunta, foram usados vários modelos iniciais diferentes para garantir melhor cobertura do espaço de soluções possíveis. Os resultados mostram uma camada de basalto com uma espessura entre 200 e 400 m, sob uma camada superficial de arenito de 50 a 100m. O embasamento da bacia está torno de 2.5 3.0 km. A espessura e razão Vp/Vs crustal da região foi estimada em 40.0 (1.0) km e 1.78 (0.02). Foi possível identificar zonas de baixa velocidade dentro do pacote de basalto, possivelmente relacionadas a zonas de fraturas ou camadas de basalto alterado. Estas camadas de baixa velocidade estão na parte sul, próximas à área de maior sismicidade induzida e também relativamente mais perto dos poços profundos de maior vazão. Isto corrobora com a hipótese de que a sismicidade local está associada à exploração de poços e estrutura de falhas pré -existentes. / A study of the seismic structure of the Paraná Basin in Bebedouro, SP, was carried out with Receiver Functions (RF). Both low frequency (with ~0.5 Hz low pass filter) and high-frequency (~10Hz) RFs were jointly inverted with surface wave dispersion curves. Surface-wave data included: long-period group velocities of Rayleigh and Love waves from continental-scale tomography in the period range 10-100 s (useful to control crustal scale structure and Moho depth), intermediate period group velocities near 1s period obtained from cross-correlation of ambient noise (useful to control sedimentary structure), phase velocities near 0.2-1.0 s obtained from local earthquakes, and phase velocities of Rayleigh waves from shallow seismic refraction data near ~0.1 s period (useful to control shallow layers). Joint inversion was obtained with several different initial models to better cover all possible solutions. The results indicate that the basalt layer is 200 to 400m thick, beneath sandstones of about 50 100m thick. The Basin basement was detected between 2.5 3.0 km depth, consistent with expected values from regional bore-hole data in the Paraná Basin. Beneath several stations a low-velocity zone was detected in the middle of the basalt pack which is interpreted as a zone of fractured or altered basalt. This anomalous low-velocity layer was detected near the most seismically active zone in the Andes district. It is also relatively close to the deep wells with larger outflow. The existence of this low-velocity zone in the middle of the basalt layer is consistent with the model proposed for the water-well induced seismicity.

L'inversion conjointe géophysique est la méthode la plus efficace pour imager l'intérieur de la Terre. En intégrant plusieurs techniques géophysiques elle permet de réduire les incertitudes inhérentes à chacune et ainsi améliorer la compréhension de la Terre. Dans cette étude, nous utilisons les techniques des fonctions récepteur (RF) en sismologie, de la magnétotellurique (MT) et de la gravimétrie qui permettent de caractériser respectivement la vitesse des ondes S, la résistivité électrique et la densité du sous-sol.Le but de ce travail de recherche se divise en deux parties: une première, méthodologique, sur le développement d'une nouvelle approche d'inversion conjointe en 3D et une deuxième avec l'application de ces techniques (en approche jointe ou séparée) sur la Divergence Nord Tanzanienne pour mieux comprendre le phénomène de rupture continentale. Pour la partie méthodologie deux approches ont été développées : une entre les données de MT et de gravimétrie avec un calcul original de l'effet gravimétrique de la topographie qui permet de réduire le nombre de mailles tout en gardant une résolution satisfaisante ; et une deuxième méthode entre les données de MT et de RF par une nouvelle approche d'extrapolation des modèles 1D de vitesse en pseudo modèle 3D de vitesse. L'application de ces techniques sur la Tanzanie a permis de mettre en évidence un certain nombre de structures lithosphériques dont deux zones majeures à faible vitesse dans la croûte inférieure et dans le manteau supérieur. Cette dernière semble refléter des interactions entre des structures héritées d'âge protérozoïque et le panache mantellique Africain. / Geophysical joint inversion attempts to reproduce as best as possible the interior of the Earth. By integrating several geophysical techniques the joint inversion reduces the uncertainties of each methods and improves our understanding of the Earth structure. In this study we use the receiver functions (RF), the magnetotelluric (MT) and the gravity methods which enable to charaterize the Swave velocity, the electrical resistivity and the density, respectively. The objective of this research work is divided in two parts; first with the development of a new 3D joint inversion approach and then with the application of these methods (on a joint or separate approach) on the North Tanzanian Divergence to better understand the continental breakup.For the methodologic part two approaches have been developed; one between the MT and gravity data with an original computation of the topographic effect which decreases the number of cells while keeping a satisfaying resolution. And a second method between the MT and RF data where pseudo 3D velocity model are created and combined with the MT models to better takes into account the physical properties of the receiver function. The application of these methods on the Tanzania highlighted several lithospheric structures and particularly two low-velocity areas in the lower crust and the upper mantle. This latter suggests interactions with Proterozoic inherited structures and the African plume material.

Abstract The crustal and upper mantle structures of the Shield on the regional scale were investigated using the data of the POLENET/LAPNET passive seismic array and the previously published models of active and passive seismic experiments in the study area. This area is centred in northern Finland and it extends to surrounding areas in Sweden, Norway and northwestern Russia. The bedrock there is mostly of the Archaean origin and the lithosphere of the region was reworked by two orogenies during Palaeoproterozoic. One of the results of the thesis was a new map of the Moho depth of the study area, for which new estimates of the crustal thickness were obtained using receiver function method and complemented by published results of receiver function studies and controlled source seismic profiles. The map differs from the previously published maps in two locations, where we found significant deepening of the Moho. The 3D structure of the upper mantle was studied using teleseismic traveltime tomography method. The resulting model shows high seismic velocities below three cratonic units of the study area, which may correspond to non-reworked fragments of cratonic lithosphere and a low velocity anomaly separating these cratonic units from each other. The regional scale studies were complemented by two smaller scale studies in upper crust level using combined interpretation of seismic profiling and gravity data. These studies were centred on Archaean Kuhmo Greenstone Belt in eastern Finland and central Lapland in northern Finland located in the crust reworked during Palaeoproterozoic. Both areas are considered as prospective ones for mineral exploration. Both studies demonstrate the advantage of gravity data inversion in studying 3D density structure of geologically interesting formations, when the Bouguer anomaly data is combined with a priori information from petrophysical and seismic datasets.

La géologie, et plus particulièrement la géophysique, repose sur l’observation, directe et indirecte, de phénomènes se produisant en surface et dans les profondeurs de la Terre. Ces observations nous permettent d’étudier et définir la structure et les dynamiques globales de la Terre. L’étude des ondes sismiques générées par les tremblements de terre les plus puissants permet, par exemple, d’entrevoir la structure des hétérogénéités dans les premières centaines de kilomètres de la Terre. Dans cette thèse, nous nous intéressons au champ d’onde diffracté, qui est composé des arrivées tardives qui suivent les ondes incidentes. Par définition, les ondes diffractés contiennent de l’information liée aux hétérogénéités diffractantes, autrement dit les structures à petite échelle de la Terre, qu’elles rencontrent le long de leur trajet. De ce fait, il est possible d’étudier les variations rapides de vitesses sismiques grâce au champ d’onde diffracté, alors que ces informations seraient perdues dans les méthodes tomographiques à cause des facteurs de régularisation. Afin d’exploiter le champ d’onde diffracté, on a recours aux fonctions récepteurs (« receiver function » en anglais, RF) et à la migration sismique en profondeur de pré-empilage. Les procédures standard de migration sismiques sont de deux types principaux. Le premier type de procédures, dont l’exemple type est la migration en point de conversion communs (« common conversion point » en anglais, CCP) est rapide mais repose sur l’hypothèse fondamentale que les discontinuités que l’on cherche à imager sont horizontales. Le second type de procédures, pour lesquelles on peut citer la « reverse time migration » (RTM), ou la « generalized radon transform » (GRT), ne font pas d’hypothèse sur la structure du sous-sol, mais demandent une forte intensité des calculs et sont de fait souvent limités à des géométries bidimensionnelles. Au cours de ce manuscrit, nous développons une migration sismique de type Kirchhoff qui se base sur des calculs de temps de trajet sismique rapides en trois dimensions et quasiment aucune hypothèse sur la structure du milieu sous-jacent. Cet algorithme efficace nous permet de nous affranchir des traditionnelles limitations à des études 1D ou 2D. Notre principe d’imagerie prend en compte les ondes diffractées transmises et réfléchies, et se place dans la suite des travaux de Cheng et al. (2016). Nous adaptons la migration de type Kirchhoff élastique aux géométries de diffraction inhérentes à la sismologie passive et prenons en compte les multiples de surface. Les temps de trajet de toutes les ondes diffractées sont calculées grâce à la « fast marching method » (FMM). Les amplitudes et la polarité des signaux des RF sont corrigées à l’aide du calcul de figures de diffraction 3D. Pour extraire l’information des conversions transmises et réfléchies de façon cohérente, les résultats pour chaque mode de diffraction sont sommés de plusieurs façons (linéaire, à filtre de phase, et à filtre d’amplitude non linéaire). Afin de démontrer l’efficacité et la précision de notre méthode de migration, nous procédons à des tests synthétiques, aussi bien dans des situations réalistes qu’artificiellement compliquées, en nous servant du logiciel Raysum. Les résultats de ces tests prouvent que cette méthode de migration permet d’obtenir une image fidèle du milieu imagé quasiment sans artéfacts. En intégrant les trois composantes des RF dans la migration, cette méthode de migration est capable d’exploiter l’information d’ondes arrivant avec n’importe quel angle d’incidence et n’importe quel azimut. Finalement, cette méthode de migration multi-mode 3D est appliquée à deux jeux de données de terrain issus de réseaux sismiques déployés au dessus de zones de subduction, en Grèce et en Alaska / In geology, and in particular in geophysics, direct and indirect observations of processes occurring both at the surface of the Earth and at depth are used to understand the structure and dynamics of the Earth. For instance, seismic waves generated by large earthquakes can be used to study the structure of heterogeneities in the first few hundred kilometers inside the Earth. In this work, we use the scattered wavefield, which corresponds to energy arriving after the incident wavefield, to image the Earth. By nature, the scattered waves are linked to the scattering heterogeneities encountered along their propagation path, i.e. the fine scale structure of the Earth. Hence, the scattered wavefield has the ability to highlight structures where rapid velocity variations would otherwise be smoothed out by tomographic regularization, such as the structure of subducting slabs. To extract the information from the scattered wavefield, we resort to receiver function (RF) analysis and pre-stack depth migration. Standard migration procedures either rely on the assumption that underlying discontinuities are horizontal, such as in Common Conversion Point stacking (CCP), or are computationally expensive and usually limited to 2D geometries, such as in Reverse Time Migration (RTM) or Generalized Radon Transform (GRT). Here, we develop a Kirchhoff-type teleseismic imaging method that uses fast 3D travel-time calculations with minimal assumptions about the underlying structure. This provides high computational efficiency without limiting the problem to 1D or 2D geometries. In our method, we apply elastic Kirchhoff migration to transmitted and reflected teleseismic waves (i.e., RF). The approach expands on the work of Cheng et al. (2016). The 3D elastic Kirchhoff migration is adapted to the passive seismology scattering geometry and to account for free surface multiples. We use an Eikonal solver based on the fast marching method (FMM) to compute travel times for all scattered phases. 3D scattering patterns are computed to correct the amplitudes and polarities of the three component input signals. We consider three different stacking methods (linear, phase weighted and 2 nd root) to enhance the structures that are most coherent across scattering modes. To showcase the efficiency and accuracy of our migration procedure, we test it by conducting a series of synthetic tests in both artificially challenging and realistic scenarios. Results from synthetic tests show that our imaging principle can recover scattering structures accurately with minimal artifacts. We show that integrating the three components of the RF into the imaging principle allows to coherently retrieve the scattering potential for arbitrarily dipping discontinuities from all back-azimuths, and are able to retrieve a typical 2.5D subduction zone structure. We apply this novel 3D multi-mode Kirchhoff migration method to two different subduction zones, in Western Greece and Southern Alaska

Orientador: João Carlos Dourado / Resumo: Técnicas sismológicas como Função do Receptor, Análise de Dispersão de Ondas de Superfície, Correlação de ruídos sísmicos e razão espectral H/V são cada vez mais estudadas e utilizadas para o conhecimento geológico da crosta. Sendo possível determinar a composição crustal média e os principais contatos obtidos por fortes contrastes de impedância tais como limite crosta superior e inferior, assim como, limite crosta inferior e manto superior (descontinuidade de Moho). O conhecimento da velocidade de percurso das ondas de um sismo registrados através de uma estação sismográfica fornecem informações, como: o tempo de percurso, relação Vp/Vs e outros. A região de Pontes e Lacerda/MT está localizada no Sudoeste do Cráton Amazônico e o levantamento dos dados se deram em fases distintas com implantação de sismômetros alinhados em direção perpendicular (NE-SW) às principais estruturas da Faixa Móvel Aguapeí (NNW-SSE). Além da coleta de dados dessas estações temporárias foram compilados dados de sismos para a estação fixa PTLB, esta estação faz parte das estações sismológicas coordenadas pela UNB (Universidade Nacional de Brasília) e pela USP (Universidade de São Paulo). A espessura média encontrada na crosta para a região variou pouco para as diferentes técnicas abordadas, sendo que, para a técnica de Função do Receptor (estação fixa PTLB) foi obtido valor de aproximadamente 44 Km de espessura e, para as estações temporárias (S01 ao S10) valor médio de 42 km. Já a seção sísmica gerad... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Seismic techniques such as receiver function, surface wave dispersion, seismic noise correlation and H / V spectral ratio are increasingly studied and used for geological knowledge of the crust. It is possible to determine the average crustal composition and the main contacts obtained by strong impedance contrasts as upper and lower crust boundary, as well as, lower crust limit and upper mantle (Moho discontinuity). The knowledge of the speed of travel of the waves of an earthquake recorded through a seismographic station provides information, such as: the travel time, Vp / Vs ratio and others. The region of Pontes e Lacerda / MT is located in the Southwest of the Amazonian craton and the data were taken in different phases with the implantation of seismometers aligned in a perpendicular direction (NE-SW direction) to the main structures of the Faixa Móvel Aguapeí (direction NNW- SSE). In addition to collecting data from these temporary stations, earthquake data were collected for the PTLB fixed station. The average thickness found in the crust for the region did not vary much for the different techniques, and for the Receiver Function (PTLB fixed station), a value of approximately 44 Km of thickness was obtained and for the temporary stations (S01 to S10) average value of 42 km. The seismic section generated by the correlation of the signals for all short-time temporary stations brought the signals coherence in 4s, 5s and later coherence ranging from 9.5 to 11 seconds. This ... (Complete abstract click electronic access below) / Doutor

Le Liban n'a pas souffert de grands tremblements de terre destructeurs depuis près de deux siècles. Il est toutefois traversé par la faille transformante majeure du Levant, séparant sur1000 km de longueur la plaque Arabique à l’est de la plaque Africaine à l’ouest. Ses principales branches au Liban sont la faille de Yammouneh qui traverse le pays du sud au nord, les failles de Serghaya et Rachaya dans sa partie Est, la faille de Roum et les failles inverses du Mont Liban dans la partie Ouest. Ces failles ont généré des séismes destructeurs dans la longue histoire connue de la région, parmi lesquels les plus importants sont ceux deJuillet 551 sur la faille du Mont-Liban, de mai 1202 sur la faille de Yammouneh, d’Octobre1759 sur la faille de Rachaya et de Novembre 1759 sur la faille de Serghaya. L'évaluation del'aléa et du risque sismique local est donc de première importance pour l'ensemble du pays.L'objectif du travail effectué dans cette thèse est d'appliquer au Liban les avancées réalisées ces dernières années dans le développement de nouveaux outils à la fois fiables et économiquement abordables pour l’évaluation de l’aléa sismique, en commençant par les grandes villes et en particulier la capitale Beyrouth. L'objectif est de mieux appréhender et comprendre le risque sismique sur le territoire libanais, pour pouvoir ensuite commencer à élaborer des politiques de prévention et des codes parasismiques qui puissent le réduire à terme.Un réseau sismologique temporaire composé de 10 stations a été installé dans Beyrouth etune partie de sa banlieue sur des sites représentatifs des principales unités géologiques présentes. Plusieurs dizaines de séismes locaux et régionaux ont pu y être enregistrés, et leur réponse sismique a été évaluée par la méthode du rapport spectral site sur référence (SSR),comparé au rapport spectral de la composante horizontale sur la composante verticale (H/V)calculé sur les tremblements de terre et sur le bruit ambiant. Les mêmes enregistrements ont également été utilisés pour prédire, par la technique des Fonctions de Green empiriques(FGE), le mouvement sismique correspondant à un événement majeur (Mw7.5) sur la faille de Yammouneh. Cet exercice de prédiction a toutefois été réalisé en deux étapes en raison des limitations dans l'application de la technique FGE en champ proche, avec deux techniques complémentaires: l'enregistrement d’un petit événement a été d'abord utilisé pour simuler un séisme de Mw6.5 sur la faille de Yammouneh, en parallèle à l'utilisation de plusieurs équations de prédiction de mouvement du sol (GMPE), soigneusement sélectionnées, pour effectuer une prédiction similaire. La comparaison FGE/GMPE a alors permis de calibrer la prédiction du mouvement du sol par GMPE à différents sites de Beyrouth pour l'événement cible de Mw7.5. Ces résultats ponctuels ont ensuite été étendus à l'ensemble de la municipalité de Beyrouth et de sa banlieue proche, en vue de mieux cerner les contours d'une future carte de microzonage, au travers d'une vaste campagne de mesures de bruit ambiant sur615 sites. Leur traitement H/V a permis d’obtenir une carte de la fréquence de résonance pour l'ensemble de la zone, carte dont la robustesse a été testée et prouvée. Des mesures sismiques actives et passives ont en outre été menées sur les principales unités géologiques à proximité des 10 sites préalablement sélectionnés et instrumentés, permettant ainsi d'obtenir les premières estimations directes de la vitesse des ondes de cisaillement (via les courbes de dispersion des ondes de Rayleigh). La comparaison de ces mesures avec les estimations -très dispersées - issues de la compilation des paramètres géologiques/géotechniques disponibles et des équations de corrélation existantes avec les valeurs N des SPT, montre tout l'intérêt de ces mesures simples et fiables. / Lebanon is one of the countries that have not suffered from large destructive earthquakes foralmost two centuries. It is however lying on the 1000 km long, left lateral Levant fault thatseparates the Arabic plate in the east from the African plate in the west. Its main branches inLebanon are the Yammouneh fault that crosses the country from south to north, the Serghayaand Rachaya faults in its Eastern part, the Roum and Mount Lebanon Thrust faults in itsWestern part. These faults have generated destructive earthquakes in the long known historyof the area. The largest events are: The July 551 earthquake on the Mount Lebanon Thrustfault, the May 1202 earthquake on the Yammouneh fault, the October 1759 on the Rachayafault and the November 1759 on the Serghaya fault. From all above, one can conclude thatLebanon is exposed to a significant seismic hazard. Assessing the local seismic hazard andrisk is therefore of primary importance for the whole country.The objective of the work undergone in this PhD is to take advantage of the latest advancesachieved worldwide to promote rather inexpensive, though reliable, seismic hazardassessment tools, to try to apply them in Lebanon starting with the big cities and specificallythe capital Beirut. These studies will help to understand the Lebanese seismic risk andsubsequently to start to elaborate seismic policies and codes that may help reducing this risk.A temporary seismological network consisting of 10 stations has been installed in Beirut anda part of its suburbs. Several tens of local and regional earthquakes could be recorded, andallowed to estimate the site response at selected sites in Beirut through the standard site toreference spectral ratio method ("SSR") on earthquakes, compared to the horizontal tovertical ratio ("H/V") calculated on earthquakes and on ambient noise. The same recordingscould also be used via the empirical Green Function’s technique ("EGF") to predict theseismic ground motion corresponding to a Mw7.5 on the Yammouneh fault. However, due tolimitations in near-field applications of the EGF technique, this prediction exercise wasperformed in two steps and with two complementary techniques: a weak event recording wasfirst used to simulate a Mw6.5 earthquake on the Yammouneh fault, while several, carefullyselected ground motion prediction equations (GMPE) were used to perform a comparativeprediction for the same earthquake. This EGF/GMPE comparison then allowed tuning theGMPE prediction of ground motion at various sites within Beirut for the target Mw7.5 event.The results were then extended in view of proposing a framework for a future microzonationviimap. A comprehensive campaign of ambient noise measurements was achieved for 615 sitesof Beirut municipality and close suburbs, the H/V processing of which allowed to derive arobust map of resonance frequency for the whole area. In addition, active and passive seismicmeasurements were conducted on different geological units near the 10 formerlyinstrumented sites, which provided quantitative estimates of the shallow S-wave velocitythrough the Rayleigh wave dispersion curves. These geophysical measurements permitted toprovide direct estimates of the shear waves velocity, which prove much more reliable thanthe highly scattered estimates derived from the compilation of the availablegeological/geotechnical parameters and the use of existing correlations equations betweenSPT N-value and S-wave velocity Vs.