L’ambition de ce travail est la prédiction du champ d’onde incident réalistique, induit par des mouvement forts de sol, aux sites d’importance stratégique, comme des centrales nucléaires. À cette fin, un plateforme multi-outil est développé et exploité pour simuler les aspects différents d’un phénomène complexe et multi-échelle comme un tremblement de terre. Ce cadre computationnel fait face à la nature diversifiée d’un tremblement de terre par approche holistique local-régionale.Un cas d’étude complexe est choisie: le tremblement de terre MW6.6 Niigata-Ken Ch¯uetsu-Oki, qui a endommagé la centrale nucléaire de Kashiwazaki-Kariwa. Les effets de site non-linéaires observés sont à premier examinés et caractérisés. Dans la suite, le modèle 3D «de la faille au site» est construit et employé pour prédire le mouvement sismique dans une bande de fréquence de 0-7 Hz. L’effet de la structure géologique pliée au-dessous du site est quantifié en simulant deux chocs d’intensité modérée et en évaluant la variabilité spatiale des spectres de réponse aux différents endroits dans le site nucléaire. Le résultat numérique souligne le besoin d’une description plus détaillée du champ d’onde incident utilisé comme paramètre d’entrée dans la conception structurel antisismique de réacteurs nucléaires et des installations. Finalement, la bande de fréquences des signaux synthétiques obtenues comme résultat des simulations numériques est agrandie en exploitant la prédiction stochastique des ordonnées spectrales à courte période fournies par des Réseaux Artificiels de Neurones. / The ambition of this work is the prediction of a synthetic yet realistic broad-band incident wave-field, induced by strong ground motion earthquakes at sites of strategic importance, such as nuclear power plants. To this end, an multi-tool platform is developed and exploited to simulate the different aspects of the complex and multi-scale phenomenon an earthquake embodies. This multi-scale computational framework copes with the manifold nature of an earthquake by a holistic local-to-regional approach. A complex case study is chosen to this end: is the MW6.6 Niigata-Ken Ch¯uetsu-Oki earthquake, which damaged the Kashiwazaki-Kariwa nuclear power plant. The observed non-linear site-effects are at first investigated and characterized. In the following, the 3D source-to-site model is constructed and employed to provide reliable input ground motion, for a frequency band of 0-7 Hz. The effect of the folded geological structure underneath the site is quantified by simulating two aftershocks of moderate intensity and by estimating the spatial variability of the response spectra at different locations within the nuclear site. The numerical outcome stresses the need for a more detailed description of the incident wave-field used as input parameter in the antiseismic structural design of nuclear reactors and facilities. Finally, the frequency band of the time-histories obtained as outcome of the numerical simulations is enlarged by exploiting the stochastic prediction of short-period response ordinates provided by Artificial Neural Networks.

This thesis addresses two fundamental topics in Engineering Seismology; the application of Probabilistic Seismic Hazard Analysis (PSHA) methodology, and the estimation of measures of Strong Ground Motion. These two topics, while being related, are presented as separate sections. In the first section, state-of-the-art PSHA methodologies are applied to various sites in the Buller Region, South Island, New Zealand. These sites are deemed critical to the maintenance of economic stability in the region. A fault-source based seismicity model is developed for the region that is consistent with the governing tectonic loading, and seismic moment release of the region. In attempting to ensure this consistency the apparent anomaly between the rates of activity dictated by deformation throughout the Quaternary, and rates of activity dictated by observed seismicity is addressed. Individual fault source activity is determined following the application of a Bayesian Inference procedure in which observed earthquake events are attributed to causative faults in the study region. The activity of fault sources, in general, is assumed to be governed by bounded power law behaviour. An exception is made for the Alpine Fault which is modelled as a purely characteristic source. The calculation of rates of exceedance of various ground motion indices is made using a combination of Poissonian and time-dependent earthquake occurrence models. The various ground motion indices for which rates of exceedance are determined include peak ground acceleration, ordinates of 5% damped Spectral Acceleration, and Arias Intensity. The total hazard determined for each of these ground motion measures is decomposed using a four dimensional disaggregation procedure. From this disaggregation procedure, design earthquake scenarios are specified for the sites that are considered. The second part of the thesis is concerned with the estimation of ground motion measures that are more informative than the existing scalar measures that are available for use in New Zealand. Models are developed for the prediction of Fourier Amplitude Spectra (FAS) as well as Arias Intensity for use in the New Zealand environment. The FAS model can be used to generate ground motion time histories for use in structural and geotechnical analyses. Arias Intensity has been shown to be an important strong motion measure due to its positive correlation with damage in short period structures as well as its utility in predicting the onset of liquefaction and landslides. The models are based upon the analysis of a dataset of New Zealand Strong Motion records as well as supplementary near field records from major overseas events. While the two measures of ground motion intensity are strongly related, different methods have been adopted in order to develop the models. As part of the methodology used for the FAS model, Monte Carlo simulation coupled with a simple ray tracing procedure is employed to estimate source spectra from various New Zealand earthquakes and, consequently, a magnitude - corner-frequency relationship is obtained. In general, the parameters of the predictive equations are determined using the most state-of-the-art mixed effects regression procedures.