Marine seismic source arrays are directional. Source directivity is used to attenuate coherent noise, but primary reflected data may be degraded. Source directivity is ignored in a standard processing sequence, so directional source signature deconvolution may be required. In the frequency-wavenumber (f-k) directional deconvolution method, a filter is calculated from far-field source signatures and is applied to the f-k transform of common-receiver gathers. Reflections on common-receiver gathers are often spatially aliased, and this causes practical problems with the technique. Directional deconvolution may also be performed in combination with prestack migration because the prestack Kirchhoff summation migration operator is a function of source take-off angle. The constant-offset section is deconvolved separately with a full range of filters for source signatures radiated in different directions; then the migration summation operator sums across the deconvolved sections, selecting the section which has been deconvolved for the correct source signature at each point. Physical model data, which were acquired over simple models using a directional source, are used to evaluate directional deconvolution assuming constant velocity. Reflector continuity and resolution are improved by using directional deconvolution. Directional deconvolution combined with prestack migration is extended to media in which the velocity varies with depth, and is applied to two datasets from the Southern North Sea. The second dataset, which has shallow steeply dipping reflectors, is improved by using directional deconvolution. Directional deconvolution may be combined with a Kirchhoff migration technique which assumes a linear velocity-depth model. Results are superior to conventional Kirchhoff migration because ray bending is honoured. Directional deconvolution cannot synthesise fully point-source equivalent data from data acquired with a source array without excessive noise amplification. Source arrays with a short in-line dimension should be used where possible. For data which have been acquired with a long source array, directional deconvolution is desirable.

Seismic traveltime inversion, traveltime tomography and seismic reflection techniques have been applied for two dimensional (2D) and three dimensional (3D) data acquired in conjunction with site characterization and monitoring aspects at a carbon dioxide (CO2) geological storage site at Ketzin, Germany (the CO2SINK project). Conventional seismic methods that focused on investigating the CO2 storage and caprock formations showed a poor or no image of the upper 150 m. In order to fill this information gap, an effort on imaging the shallow subsurface at a potentially risky area at the site is the principal goal of this thesis. Beside this objective, a seismic source comparison from a 2D pilot study for acquisition parameter testing at the site found a weight drop source suitable with respect to the signal penetration, frequency content of the data and minimizing time and cost for 3D data acquisition. For the Ketzin seismic data, the ability to obtain high-quality images is limited by the acquisition geometry, source-generated noise and time shifts due to near-surface effects producing severe distortions in the data. Moreover, these time shifts are comparable to the dominant periods of the reflections and to the size of structures to be imaged. Therefore, a combination of seismic refraction and state-of-the-art processing techniques, including careful static corrections and more accurate velocity analysis, resulted in key improvements of the images and allowed new information to be extracted. The results from these studies together with borehole information, hydrogeologic models and seismic modeling have been combined into an integrated interpretation. The boundary between the Quaternary and Tertiary unit has been mapped. The internal structure of the Quaternary sediments is likely to be complicated due to the shallow aquifer/aquitard complex, whereas the heterogeneity in the Tertiary unit is due to rock alteration associated with fault zones. Some of the major faults appear to project into the Tertiary unit. These findings are important for understanding the potentially risky anticline crest and can be used as a database for the future monitoring program at the site.

<p>Seismic traveltime inversion, traveltime tomography and seismic reflection techniques have been applied for two dimensional (2D) and three dimensional (3D) data acquired in conjunction with site characterization and monitoring aspects at a carbon dioxide (CO₂) geological storage site at Ketzin, Germany (the CO₂SINK project). Conventional seismic methods that focused on investigating the CO₂ storage and caprock formations showed a poor or no image of the upper 150 m. In order to fill this information gap, an effort on imaging the shallow subsurface at a potentially risky area at the site is the principal goal of this thesis.</p><p>Beside this objective, a seismic source comparison from a 2D pilot study for acquisition parameter testing at the site found a weight drop source suitable with respect to the signal penetration, frequency content of the data and minimizing time and cost for 3D data acquisition.</p><p>For the Ketzin seismic data, the ability to obtain high-quality images is limited by the acquisition geometry, source-generated noise and time shifts due to near-surface effects producing severe distortions in the data. Moreover, these time shifts are comparable to the dominant periods of the reflections and to the size of structures to be imaged. Therefore, a combination of seismic refraction and state-of-the-art processing techniques, including careful static corrections and more accurate velocity analysis, resulted in key improvements of the images and allowed new information to be extracted. The results from these studies together with borehole information, hydrogeologic models and seismic modeling have been combined into an integrated interpretation. The boundary between the Quaternary and Tertiary unit has been mapped. The internal structure of the Quaternary sediments is likely to be complicated due to the shallow aquifer/aquitard complex, whereas the heterogeneity in the Tertiary unit is due to rock alteration associated with fault zones. Some of the major faults appear to project into the Tertiary unit. These findings are important for understanding the potentially risky anticline crest and can be used as a database for the future monitoring program at the site.</p>

Due to the randomness inherent in the occurrence of earthquakes with respect to time, space and magnitude as well as other various sources of uncertainties, seismic hazard assessment should be carried out in a probabilistic manner. Basic steps of probabilistic seismic hazard analysis are the delineation of seismic sources, assessment of the earthquake occurrence characteristics for each seismic source, selection of the appropriate ground motion attenuation relationship and identification of the site characteristics. Seismic sources can be modeled as area and line sources. Also, the seismic activity that can not be related with any major seismic sources can be treated as background source in which the seismicity is assumed to be uniform or spatially smoothed. Exponentially distributed magnitude and characteristic earthquake models are often used to describe the magnitude recurrence relationship. Poisson and renewal models are used to model the occurrence of earthquakes in the time domain. In this study, the sensitivity of seismic hazard results to the models associated with the different assumptions mentioned above is investigated. The effects of different sources of uncertainties involved in probabilistic seismic hazard analysis methodology to the results are investigated for a number of sites with different distances to a single fault. Two case studies are carried out to examine the influence of different assumptions on the final results based on real data as well as to illustrate the implementation of probabilistic seismic hazard analysis methodology for a large region (e.g. a country) and a smaller region (e.g. a province).

Efficiency of probabilistic seismic hazard analysis mainly depends on the individual successes of its complementing components / such as source characterization and ground motion intensity prediction. This study contributes to major components of the seismic hazard workflow including magnitude &ndash / rupture dimension scaling relationships, and ground motion intensity prediction. The study includes revised independent models for predicting rupture dimensions in shallow crustal zones, accompanied by proposals for geometrically compatible rupture area-length-width models which satisfy the rectangular rupture geometry assumption. Second main part of the study focuses on developing a new ground motion prediction model using data from Turkish strong ground motion database. The series of efforts include, i) compilation and processing of a strong motion dataset, ii) quantifying parameter uncertainties of predictive parameters such as magnitude and source to site distance / and predicted accelerations due to uncertainty in site conditions and response, as well as uncertainty due to random orientation of the sensor, iii) developing a ground response model as a continuous function of peak ground acceleration and shear wave velocity, and finally, iv) removing bias in predictions due to uneven sampling of the dataset. Auxiliary components of the study include a systematic approach to source characterization problem, with products ranging from description of systematically idealized and documented seismogenic faults in Anatolia, to delineation, magnitude-recurrence parameterization, and selection of maximum magnitude earthquakes. Last stage of the study covers the development of a custom computer code for probabilistic seismic hazard assessment which meets the demands of modern state of practice.

No description available.

Spatial clustering of seismic events in mines has been widely reported in literature. Despite obvious visual correlations between spatial clusters of seismic events and geomechanical structures in mines (such as pillars, dykes and faults), very limited research has been undertaken to utilise this information to filter seismic data. A linkage between spatial seismic event clusters and discrete rockmass failure mechanisms is tenuous and not well established using current seismic analysis techniques. A seismic event clustering methodology is proposed. The first component of the methodology uses a complete-linkage (CLINK) clustering routine to identify relatively compact clusters of seismic events. The CLINK clusters are then subjected to a singlelink clustering process, which uses spatial location and seismic source parameters as similarity measures. The resultant

Bolu-Ilgaz region was damaged by several large earthquakes in the last century and the structural damage was substantial especially after the 1944 and 1999 earthquakes. The objective of this study is to build the seismic source characterization model for the rupture zone of 1944 Bolu-Gerede earthquake and perform probabilistic seismic hazard assessment (PSHA) in the region. One of the major improvements over the previous PSHA practices accomplished in this study is the development of advanced seismic source models in terms of source geometry and reoccurrence relations. Geometry of the linear fault segments are determined and incorporated with the help of available fault maps. Composite magnitude distribution model is used to properly represent the characteristic behavior of NAF without an additional background zone. Fault segments, rupture sources, rupture scenarios and fault rupture models are determined using the WG-2003 terminology. The Turkey-Adjusted NGAW1 (G&uuml / lerce et al., 2013) prediction models are employed for the first time on NAF system. The results of the study is presented in terms of hazard curves, deaggregation of the hazard and uniform hazard spectrum for four main locations in the region to provide basis for evaluation of the seismic design of special structures in the area. Hazard maps of the region for rock site conditions and for the proposed site characterization model are provided to allow the user perform site-specific hazard assessment for local site conditions and develop site-specific design spectrum. The results of the study will be useful to manage the future seismic hazard in the region.

The North Anatolian Fault System is one of the most important active strike-slip fault systems in the world. The August 17, 1999 and November 12, 1999 earthquakes at Kocaeli and D&uuml / zce are the most recent devastating earthquakes. The study area lies in the Eastern Marmara Region and is bounded by the 28.55-33.75 E and 40.00-41.20 N, latitude and longitude coordinates, respectively. There are numerous studies conducted in the study area in terms of active tectonics and seismicity, however studies are scale dependent. Therefore, a comprehensive literature survey regarding active tectonics of the region was conducted and these previous studies were combined with the lineaments extracted from 10 ASTER images via principle component analysis manual extraction method. Therefore, a line seismic source model for the Eastern Marmara region was compiled mainly based on major seismic events of instrumental period. The seismicity of these line segments were compared with the instrumental period earthquake catalogue compiled by Kandilli Observatory and Earthquake Research Institute with a homogeneous magnitude scale between 1900 and 2005. Secondary event and completeness of this catalogue was checked. The final catalogue was matched with the compiled seismic source for historical seismicity and source-scenario-segment-weight relationships were developed. This developed seismic source model was tested by a probabilistic seismic hazard assessment for D&uuml / zce city center by utilizing four different ground motion prediction equations. It was observed that Gutenberg-Richter seismicity parameter &lsquo / b&rsquo / does not have significant effect over the model, however change in the segmentation model have a low but certain influence.

La caractérisation des tremblements de terre est un domaine de recherche primordial en sismologie, où l'objectif final est de fournir des estimations précises d'attributs de la source sismique. Dans ce domaine, certaines questions émergent, par exemple : quand un tremblement de terre s’est-il produit? quelle était sa taille? ou quelle était son évolution dans le temps et l'espace? On pourrait se poser d'autres questions plus complexes comme: pourquoi le tremblement s'est produit? quand sera le prochain dans une certaine région? Afin de répondre aux premières questions, une représentation physique du phénomène est nécessaire. La construction de ce modèle est l'objectif scientifique de ce travail doctoral qui est réalisé dans le cadre de la modélisation cinématique. Pour effectuer cette caractérisation, les modèles cinématiques de la source sismique sont un des outils utilisés par les sismologues. Il s’agit de comprendre la source sismique comme une dislocation en propagation sur la géométrie d’une faille active. Les modèles de sources cinématiques sont une représentation physique de l’histoire temporelle et spatiale d’une telle rupture en propagation. Cette modélisation est dite approche cinématique car les histoires de la rupture inférées par ce type de technique sont obtenues sans tenir compte des forces qui causent l'origine du séisme.Dans cette thèse, je présente une nouvelle méthode d'inversion cinématique capable d'assimiler, hiérarchiquement en temps, les traces de données à travers des fenêtres de temps évolutives. Cette formulation relie la fonction de taux de glissement et les sismogrammes observés, en préservant la positivité de cette fonction et la causalité quand on parcourt l'espace de modèles. Cette approche, profite de la structure creuse de l’histoire spatio-temporelle de la rupture sismique ainsi que de la causalité entre la rupture et chaque enregistrement différé par l'opérateur. Cet opérateur de propagation des ondes connu, est différent pour chaque station. Cette formulation progressive, à la fois sur l’espace de données et sur l’espace de modèle, requiert des hypothèses modérées sur les fonctions de taux de glissement attendues, ainsi que des stratégies de préconditionnement sur le gradient local estimé pour chaque paramètre du taux de glissement. Ces hypothèses sont basées sur de simples modèles physiques de rupture attendus. Les applications réussies de cette méthode aux cas synthétiques (Source Inversion Validation Exercise project) et aux données réelles du séisme de Kumamoto 2016 (Mw=7.0), ont permis d’illustrer les avantages de cette approche alternative d’une inversion cinématique linéaire de la source sismique.L’objectif sous-jacent de cette nouvelle formulation sera la quantification des incertitudes d’un tel modèle. Afin de mettre en évidence les propriétés clés prises en compte dans cette approche linéaire, dans ce travail, j'explore l'application de la stratégie bayésienne connue comme Hamiltonian Monte Carlo (HMC). Cette méthode semble être l’une des possibles stratégies qui peut être appliquée à ce problème linéaire sur-paramétré. Les résultats montrent qu’elle est compatible avec la stratégie linéaire dans le domaine temporel présentée ici. Grâce à une estimation efficace du gradient local de la fonction coût, on peut explorer rapidement l'espace de grande dimension des solutions possibles, tandis que la linéarité est préservée. Dans ce travail, j'explore la performance de la stratégie HMC traitant des cas synthétiques simples, afin de permettre une meilleure compréhension de tous les concepts et ajustements nécessaires pour une exploration correcte de l'espace de modèles probables. Les résultats de cette investigation préliminaire sont encourageants et ouvrent une nouvelle façon d'aborder le problème de la modélisation de la reconstruction cinématique de la source sismique, ainsi, que de l’évaluation des incertitudes associées. / The earthquake characterization is a fundamental research field in seismology, which final goal is to provide accurate estimations of earthquake attributes. In this study field, various questions may rise such as the following ones: when and where did an earthquake happen? How large was it? What is its evolution in space and time? In addition, more challenging questions can be addressed such as the following ones: why did it occur? What is the next one in a given area? In order to progress in the first list of questions, a physical description, or model, of the event is necessary. The investigation of such model (or image) is the scientific topic I investigate during my PhD in the framework of kinematic source models. Understanding the seismic source as a propagating dislocation that occurs across a given geometry of an active fault, the kinematic source models are the physical representations of the time and space history of such rupture propagation. Such physical representation is said to be a kinematic approach because the inferred rupture histories are obtained without taking into account the forces that might cause the origin of the dislocation.In this PhD dissertation, I present a new hierarchical time kinematic source inversion method able to assimilate data traces through evolutive time windows. A linear time-domain formulation relates the slip-rate function and seismograms, preserving the positivity of this function and the causality when spanning the model space: taking benefit of the time-space sparsity of the rupture model evolution is as essential as considering the causality between rupture and each record delayed by the known propagator operator different for each station. This progressive approach, both on the data space and on the model space, does require mild assumptions on prior slip-rate functions or preconditioning strategies on the slip-rate local gradient estimations. These assumptions are based on simple physical expected rupture models. Successful applications of this method to a well-known benchmark (Source Inversion Validation Exercise 1) and to the recorded data of the 2016 Kumamoto mainshock (Mw=7.0) illustrate the advantages of this alternative approach of a linear kinematic source inversion.The underlying target of this new formulation will be the future uncertainty quantification of such model reconstruction. In order to achieve this goal, as well as to highlight key properties considered in this linear time-domain approach, I explore the Hamiltonian Monte Carlo (HMC) stochastic Bayesian framework, which appears to be one of the possible and very promising strategies that can be applied to this stabilized over-parametrized optimization of a linear forward problem to assess the uncertainties on kinematic source inversions. The HMC technique shows to be compatible with the linear time-domain strategy here presented. This technique, thanks to an efficient estimation of the local gradient of the misfit function, appears to be able to rapidly explore the high-dimensional space of probable solutions, while the linearity between unknowns and observables is preserved. In this work, I investigate the performance of the HMC strategy dealing with simple synthetic cases with almost perfect illumination, in order to provide a better understanding of all the concepts and required tunning to achieve a correct exploration of the model space. The results from this preliminary investigation are promising and open a new way of tackling the kinematic source reconstruction problem and the assessment of the associated uncertainties.