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Induced seismicity (earthquakes caused by injection or extraction of fluids in Earth's subsurface) is a major, new hazard in the United States, the Netherlands, and other countries, with vast economic consequences if not properly managed. Addressing this problem requires development of predictive simulations of how fluid-saturated solids containing frictional faults respond to fluid injection/extraction. Here we present a numerical method for linear poroelasticity with rate-and-state friction faults. A numerical method for approximating the fully coupled linear poroelastic equations is derived using the summation-by-parts-simultaneous-approximation-term (SBP-SAT) framework. Well-posedness is shown for a set of physical boundary conditions in 1D and in 2D. The SBP-SAT technique is used to discretize the governing equations and show semi-discrete stability and the correctness of the implementation is verified by rigorous convergence tests using the method of manufactured solutions, which shows that the expected convergence rates are obtained for a problem with spatially variable material parameters. Mandel's problem and a line source problem are studied, where simulation results and convergence studies show satisfactory numerical properties. Furthermore, two problem setups involving fault dynamics and slip on faults triggered by fluid injection are studied, where the simulation results show that fluid injection can trigger earthquakes, having implications for induced seismicity. In addition, the results show that the scheme used for solving the fully coupled problem, captures dynamics that would not be seen in an uncoupled model. Future improvements involve imposing Dirichlet boundary conditions using a different technique, extending the scheme to handle curvilinear coordinates and three spatial dimensions, as well as improving the high-performance code and extending the study of the fault dynamics.

Three hybrid moment tensor inversion methods were developed for seismic sources originating from a small source region. These techniques attempt to compensate for various types of systematic error (or noise) that influence seismograms recorded in the underground environment in order to achieve an accurate and robust measure of the seismic moment tensor. The term 'hybrid' was used to distinguish between the relative method proposed by Dahm (1995) and the methods developed in this thesis. The hybrid methods were essentially weighting schemes designed to enhance the accuracy of the computed moment tensors by decreasing the influence of any low quality observations, to damp (or amplify) any signals that have been overestimated (or underestimated) due to local site effects, and to correct for raypath focussing or defocussing that results from inhomogeneities in the rockmass. The weighting or correction applied to a particular observation was derived from the residuals determined when observed data were compared with corresponding theoretical data (for a particular geophone site, sensor orientation and wave phase) and were calculated using a cluster of events rather than a single event. The first and second weighting schemes were indirectly related to the mean and the median of the residuals where the residuals were defined as the ratio of the theoretical to observed data. In the third scheme, the residuals were defined as the difference between the observed and theoretical data and the weights were based on the distance of a data point (measured in standard deviations) from the mean residual. In each of the weighting schemes, the correction was applied iteratively until the standard error of the least-squares solution (normalised to the scalar seismic moment) was a minimum. The schemes were non-linear because new weights were calculated for each iteration. A number of stability tests using synthetic data were carried out to quantify the source resolving capabilities of the hybrid methods under various extreme conditions. The synthetic events were pure double-couple sources having identical fault-plane orientations, and differing only in rake. This similarity in the mechanisms was chosen because the waveforms of tightly grouped events recorded underground often show high degrees of similarity. For each test, the results computed using the three hybrid methods were compared with one another and with those computed using the single event, absolute method and two relative methods (with and without a reference mechanism). In the noise-free situation, it was found that the relative method without reference mechanism showed the highest resolution of mechanisms, provided that the coverage of the focal sphere was not too sparse (> 3 stations). The hybrid method using a median correction was found to be the most robust of all the methods tested in the most extreme case of poor coverage (2 stations) of the focal sphere. When increasing levels of pseudo-random noise were applied to the data, the absolute moment tensor inversion method, the hybrid method using a median correction, and the hybrid method using a weighted mean correction all showed similar robustness and stability in extreme configurations concerning network coverage of the focal sphere and noise level. When increasing levels of systematic noise were added to the data, the hybrid methods using a median correction and weighted mean correction were found to exhibit similar robustness and stability in extreme configurations concerning network coverage of the focal sphere and systematic noise. In all situations investigated, these two hybrid methods outperformed the relative and absolute methods. The hybrid moment tensor inversion methods using a median and weighted mean correction were applied to a cluster of 14 events, having remarkably similar waveforms, recorded at Oryx Gold Mine. For comparative purposes, the absolute method was also applied. The inputs to the inversion methods consisted of the spectral plateaus of both P- and S-waves at frequencies below the comer frequency of the time-integrated displacement traces. The polarities of dominant motion were used as an additional constraint and were determined from cross-correlation of observed with synthetic P- or S-waves. The solutions computed using the hybrid moment tensor inversion using a median correction displayed a distinct improvement after the iterative residual correction procedure was applied. The radiation patterns and faultplane solutions showed a high degree of similarity, and are probably more accurate reflections of reality than those computed using the absolute moment tensor inversion methods. These observations are very encouraging and point towards the method's potential for use as a standard processing tool for mine seismicity. The implications of this work are a better understanding of the focal mechanisms of seismic events induced by mining activities, ultimately leading to improved safety underground.

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.

Ce travail de recherche étudie l’histoire des impacts environnementaux de l’extraction du charbon dans les bassins miniers du Couchant de Mons et du Valenciennois du 18e siècle jusqu’à l’Entre-deux-guerres ainsi que l’émergence de la logique extractiviste en Belgique et en France. Il met en lumière les fondements culturels et les bases scientifiques et législatives qui ont permis l’expansion de l’extraction du charbon dans ces deux pays, notamment au point de vue de la régulation des dégâts miniers. Ensuite les réactions des États, des entreprises minières et des habitants des bassins aux dégradations environnementales causées par l’extraction du charbon sont abordées. Les processus de négociation, les jeux de pouvoir et les mouvements d’opposition au charbon sont au cœur de cette interrogation. Le poids important des charbonnages dans la régulation des dégâts miniers, la volonté des gouvernements à permettre l’extraction du charbon et le développement d’une « guerre contre le charbon » par les habitants des bassins houillers sont analysés à partir de plusieurs situations exemplatives. Enfin, la thèse envisage l’influence des géologues et des ingénieurs des mines dans la création d’une « science des dégâts miniers » à travers trois controverses scientifiques : la séismicité induite, les théories des affaissements miniers et les inondations engendrées par l’extraction de la houille. / This is a study on the history of the environmental impacts of coal mining in the « Couchant de Mons » and the « Valenciennois » basins and the development of extractivism in Belgium and France from the 18th century to the Inter-war Period. It highlights the cultural foundations and the scientific and legal basis explaining the expansion of coal mining in these two countries, especially regarding the regulation of mining damages. Reactions of the States, mining companies and the inhabitants of the basins to the environmental damages caused by coal extraction are also analyzed. Processes of negotiation, power strategies and movements against coal mining are at the heart of this thesis. The heavy weight of collieries in the regulation system of mining damages, the willingness of governments to allow the extraction of coal and the development of a « War against coal » by the inhabitants are analyzed from several exemplary situations. Finally, this work considers the influence of geologists and mining engineers in the creation of a « science of mining damages » through three scientific controversies : induced seismicity, theories on mining subsidence and flooding engendered by coal mining.

Afin de mieux comprendre les interactions entre les modifications des contraintes induites par l'exploitation minière et la génération d'activité sismique, une zone profonde de la mine de Garpenberg (Suède) a été instrumentée par l’Ineris avec de sondes microsismiques et de cellules géotechniques. L’analyse spatio-temporelle des événements microsismiques enregistrés entre 2015 et 2016, ainsi que leurs paramètres à la source, ont mis en évidence deux types de réponses sismiques : une locale et courte dans le temps directement induite par les tirs de production, l’autre plus persistante et distante des excavations étant principalement contrôlée par des hétérogénéités géologiques. L’analyse des données géotechniques a montrée l’occurrence de déformations asismiques, ainsi que de phénomènes de fluage induits par l’exploitation. De plus l'activité sismique décroît proportionnellement au taux de diminution des déformations mesurées. Cette dernière observation implique que le fluage peut être un autre mécanisme menant à la sismicité, s’ajoutant au changement de contrainte immédiat induit par les tirs de production. Dans la dernière partie de cette thèse, un modèle géomécanique élasto-plastique 3D a été réalisé et ses résultats ont été comparés aux données géophysiques. Cette comparaison a montré que les modèles numériques à l'échelle de la mine peuvent être des outils puissants pour étudier la sismicité induite à grande échelle. Cependant, il y a certains aspects de la sismicité induite que le modèle ne peut expliquer entièrement. Cela est le cas pour la sismicité déclenchée à distance des excavations, alors que de meilleures corrélations sont trouvées lorsque l'on considère la sismicité à proximité des zones de production. Les résultats de cette thèse ont démontré qu'une approche combinée associent les données sismiques et géotechniques à la modélisation numérique peut améliorer considérablement notre compréhension de la réponse des massifs rocheux à l'exploitation minière. La combinaison de ces méthodologies dans une approche intégrée peut réduire considérablement leurs limites explicites qui sont évidents lorsque ces instruments sont considérés séparément. / With the aim of better understanding interactions between stress modifications induced by mining and the generation of seismic activity, a deep area of Garpenberg mine (Sweden) was instrumented by Ineris with microseismic probes and geotechnical cells. Spatiotemporal analysis of recorded seismicity between 2015 and 2016, as well as seismic source parameters, have highlighted two types of seismic rock mass responses: one local and temporally short directly induced by production blasts, the other long-lasting over time and remote from excavations being mainly controlled by geological heterogeneities. Geotechnical data analysis showed the occurrence of aseismic deformations, as well as creep phenomena induced by mining exploitation. In addition, seismic activity decays proportional to the decaying rate of measured strains. This latter observation implies that creep may be another mechanism driving seismicity, in addition to the immediate stress change induced by blasting. In the last part of this thesis, a 3D elasto-plastic geomechanical model has been realized and its results have been compared with geophysical data. This comparison showed that mine-wide numerical models can be suitable for the analysis of mining induced seismicity at large-scale. However, there are some aspects of the induced seismicity that the model cannot fully explain. This is particularly true for remote seismicity occurring at a distance from excavations, while better correlations are found when considering seismicity close to production areas. Results of this thesis demonstrated that a combined approach which associates seismic and geotechnical data with numerical modelling can significantly improve our understanding of the rock mass response to mining. The combination of these methodologies in an integrated approach can significantly reduce their straightforward limitations, which appears evident when these instruments are considered separately.

The primary objective of this study is to improve understanding of the mechanics of hydraulic fracturing in naturally-fractured reservoirs. The study focuses on enhancing the interpretation of hydraulic fracture-induced microseismic data using an S-wave Gaussian-beam method and numerical modeling techniques for interpretation. The S-wave Gaussian-beam method was comprehensively calibrated by synthetic and real data sets with different recording networks, and this showed the potential to retrieve additional microseismic data from hydraulic fracturing with linear receiver arrays. This approach could enhance current practice because a large number of induced events in these environments have very strong S-waves with P-wave amplitudes similar, or less than, background noise levels. The numerical study using the distinct element methods PFC2D and PFC3D was used to validate the understanding of the hydraulic fracturing mechanisms induced in laboratory and field fluid treatments in naturally-fractured reservoirs. This was achieved through direct comparison with the results of the geometry of hydraulic fractures and seismic source information (locations, magnitudes, and mechanisms) from both laboratory experiments and field observations. A suite of numerical models with fully-dynamic and hydro-mechanical coupling has been used to examine in detail the interaction between natural and induced fractures with the variations of the differential stresses and the orientations of the pre-fractures, and the relationship between the fluid front, the fracture tip, and the induced seismicity. The numerical results qualitatively agreed with the laboratory and field observations of the geometry of hydraulic fractures, confirmed the possible mechanics of new fracture development and their interactions with natural fractures, and illustrated the possible relationship between the fluid front and the fracture tip. The validated model could therefore help track the potential extent of induced fracturing in naturally-fractured reservoirs and the extent to which it can be detected by a microseismic monitoring array in order to assess the effectiveness of a hydraulic fracturing project.

The primary objective of this study is to improve understanding of the mechanics of hydraulic fracturing in naturally-fractured reservoirs. The study focuses on enhancing the interpretation of hydraulic fracture-induced microseismic data using an S-wave Gaussian-beam method and numerical modeling techniques for interpretation. The S-wave Gaussian-beam method was comprehensively calibrated by synthetic and real data sets with different recording networks, and this showed the potential to retrieve additional microseismic data from hydraulic fracturing with linear receiver arrays. This approach could enhance current practice because a large number of induced events in these environments have very strong S-waves with P-wave amplitudes similar, or less than, background noise levels. The numerical study using the distinct element methods PFC2D and PFC3D was used to validate the understanding of the hydraulic fracturing mechanisms induced in laboratory and field fluid treatments in naturally-fractured reservoirs. This was achieved through direct comparison with the results of the geometry of hydraulic fractures and seismic source information (locations, magnitudes, and mechanisms) from both laboratory experiments and field observations. A suite of numerical models with fully-dynamic and hydro-mechanical coupling has been used to examine in detail the interaction between natural and induced fractures with the variations of the differential stresses and the orientations of the pre-fractures, and the relationship between the fluid front, the fracture tip, and the induced seismicity. The numerical results qualitatively agreed with the laboratory and field observations of the geometry of hydraulic fractures, confirmed the possible mechanics of new fracture development and their interactions with natural fractures, and illustrated the possible relationship between the fluid front and the fracture tip. The validated model could therefore help track the potential extent of induced fracturing in naturally-fractured reservoirs and the extent to which it can be detected by a microseismic monitoring array in order to assess the effectiveness of a hydraulic fracturing project.

The central and eastern United States is subject to seismic hazards from both natural and induced earthquakes, as evidenced by the 1811-1812 New Madrid earthquake sequence, consisting of at least three magnitude 7 and greater earthquakes, and by four magnitude 5 and greater induced earthquakes in Oklahoma since 2011. To mitigate seismic hazards, both earthquake sources and their effects need to be characterized. Ground motion site response can cause additional damage to susceptible infrastructure and buildings. Recent studies indicate that Vs30, one of the primary site-response predictors used in current engineering practice, is not reliable. To investigate site response in the New Madrid Seismic Zone, ratios of surface-to-bedrock amplitude spectra, TFT, from S-wave recordings at the two deep vertical seismic arrays in the sediment-filled upper Mississippi Embayment (i.e., VSAP and CUSSO) were calculated. The mean TFT curves were compared with theoretical transfer functions; the results were comparable, indicating that TFT estimates of the empirical, linear SH-wave site responses at these sites. The suitability of surface S-wave horizontal-to-vertical spectral ratios, H/V, for estimating the empirical site transfer function was also evaluated. The results indicate that mean S-wave H/V curves are similar to TFT at low frequencies (less than the fifth natural frequencies) at both CUSSO and VSAP. SH-wave fundamental frequency, f0, and fundamental-mode amplification, A0, were evaluated as alternatives to the Vs30 proxy to estimate primary linear site-response characteristics at VSAP, CUSSO, and nine other seismic stations in the CEUS. In addition, calculated f0 and A0 were compared with the first peaks of S-wave H/V spectral ratios. The f0 and A0 were found to approximate the 1-D linear, viscoelastic, fundamental-mode responses at most stations. Also, S-wave H/V from weak-motion earthquakes can be used to measure f0. However, S-wave H/V does not reliably estimate A0 in the project area. S-wave H/V observations reveal site response within the frequency band of engineering interest from deeper, unmodeled geological structures. Because damaging or felt earthquakes induced by hydraulic fracturing and wastewater disposal have occurred in the CEUS, characterizing background seismicity prior to new large-scale subsurface fluid injection is important to identify cases of and the potential for induced seismicity. The Rogersville Shale in the Rome Trough of eastern Kentucky is being tested for unconventional oil and gas potential; production of this shale requires hydraulic fracturing, which has been linked to induced seismicity elsewhere in the CEUS. To characterize natural seismicity and to monitor induced seismicity during testing, a temporary seismic network was deployed in the Rome Trough near the locations of new, Rogersville Shale oil and gas test wells. Using the real-time recordings of this network and those of other regional seismic stations, three years of local seismicity were cataloged. Only three earthquakes occurred in the Rome Trough of eastern Kentucky, none of which was associated with the deep Rogersville Shale test wells that were stimulated during the time the network was in operation.