The purpose of this thesis is to conduct a detailed examination of the forward-directivity characteristics of near-fault ground motions produced in the 2010-11 Canterbury earthquakes, including evaluating the efficacy of several existing empirical models which form the basis of frameworks for considering directivity in seismic hazard assessment. A wavelet-based pulse classification algorithm developed by Baker (2007) is firstly used to identify and characterise ground motions which demonstrate evidence of forward-directivity effects from significant events in the Canterbury earthquake sequence. The algorithm fails to classify a large number of ground motions which clearly exhibit an early-arriving directivity pulse due to: (i) incorrect pulse extraction resulting from the presence of pulse-like features caused by other physical phenomena; and (ii) inadequacy of the pulse indicator score used to carry out binary pulse-like/non-pulse-like classification. An alternative ‘manual’ approach is proposed to ensure 'correct' pulse extraction and the classification process is also guided by examination of the horizontal velocity trajectory plots and source-to-site geometry. Based on the above analysis, 59 pulse-like ground motions are identified from the Canterbury earthquakes , which in the author's opinion, are caused by forward-directivity effects. The pulses are also characterised in terms of their period and amplitude. A revised version of the B07 algorithm developed by Shahi (2013) is also subsequently utilised but without observing any notable improvement in the pulse classification results. A series of three chapters are dedicated to assess the predictive capabilities of empirical models to predict the: (i) probability of pulse occurrence; (ii) response spectrum amplification caused by the directivity pulse; (iii) period and amplitude (peak ground velocity, PGV) of the directivity pulse using observations from four significant events in the Canterbury earthquakes. Based on the results of logistic regression analysis, it is found that the pulse probability model of Shahi (2013) provides the most improved predictions in comparison to its predecessors. Pulse probability contour maps are developed to scrutinise observations of pulses/non-pulses with predicted probabilities. A direct comparison of the observed and predicted directivity amplification of acceleration response spectra reveals the inadequacy of broadband directivity models, which form the basis of the near-fault factor in the New Zealand loadings standard, NZS1170.5:2004. In contrast, a recently developed narrowband model by Shahi & Baker (2011) provides significantly improved predictions by amplifying the response spectra within a small range of periods. The significant positive bias demonstrated by the residuals associated with all models at longer vibration periods (in the Mw7.1 Darfield and Mw6.2 Christchurch earthquakes) is likely due to the influence of basin-induced surface waves and non-linear soil response. Empirical models for the pulse period notably under-predict observations from the Darfield and Christchurch earthquakes, inferred as being a result of both the effect of nonlinear site response and influence of the Canterbury basin. In contrast, observed pulse periods from the smaller magnitude June (Mw6.0) and December (Mw5.9) 2011 earthquakes are in good agreement with predictions. Models for the pulse amplitude generally provide accurate estimates of the observations at source-to-site distances between 1 km and 10 km. At longer distances, observed PGVs are significantly under-predicted due to their slower apparent attenuation. Mixed-effects regression is employed to develop revised models for both parameters using the latest NGA-West2 pulse-like ground motion database. A pulse period relationship which accounts for the effect of faulting mechanism using rake angle as a continuous predictor variable is developed. The use of a larger database in model development, however does not result in improved predictions of pulse period for the Darfield and Christchurch earthquakes. In contrast, the revised model for PGV provides a more appropriate attenuation of the pulse amplitude with distance, and does not exhibit the bias associated with previous models. Finally, the effects of near-fault directivity are explicitly included in NZ-specific probabilistic seismic hazard analysis (PSHA) using the narrowband directivity model of Shahi & Baker (2011). Seismic hazard analyses are conducted with and without considering directivity for typical sites in Christchurch and Otira. The inadequacy of the near-fault factor in the NZS1170.5: 2004 is apparent based on a comparison with the directivity amplification obtained from PSHA.

Assessment of potential ground motions in seismically active regions is essential for purposes of seismic design and analysis. Peak ground motion intensity values and frequency content of seismic excitations are required for reliable seismic design, analysis and retrofitting of structures. In regions of sparse or no strong ground motion records, ground motion simulations provide physics-based synthetic records. These simulations provide not only the earthquake engineering parameters but also give insight into the mechanisms of the earthquakes. This thesis presents strong ground motion simulations in three regions of intense seismic activity. Stochastic finite-fault simulation methodology with a dynamic corner frequency approach is applied to three case studies performed in D&uuml / zce, L&rsquo / Aquila and Erzincan regions. In D&uuml / zce study, regional seismic source, propagation and site parameters are determined through validation of the simulations against the records. In L&rsquo / Aquila case study, in addition to study of the regional parameters, the limitations of the method in terms of simulating the directivity effects are also investigated. In Erzincan case study, where there are very few records, the optimum model parameters are determined using a large set of simulations with an error-minimization scheme. Later, a parametric sensitivity study is performed to observe the variations in simulation results to small perturbations in input parameters. Results of this study confirm that stochastic finite-fault simulation method is an effective technique for generating realistic physics-based synthetic records of large earthquakes in near field regions.

L’une des problématique scientifique majeure en sismologie est de pouvoir estimer les mouvements du sol attendus en un site pour un futur séisme. L’objectif de cette thèse est de tester et de valider deux méthodes de simulation des mouvements du sol basées sur l’approche des fonctions de Green empiriques et d’apporter des éléments pouvant aider au développement d’une méthodologie de simulation en aveugle. Dans une première partie, une méthode de simulation basée sur une approche stochastique en point-source est validée sur les données réelles de séismes récents bien instrumentés : le séisme des Saintes Mw6.4 et le séisme de L’Aquila Mw6.3. Nous avons développé une approche de simulation en aveugle en prenant en compte une incertitude sur le paramètre de rapport des chutes de contrainte C. Cette approche permet de générer un ensemble d’accélérogrammes synthétiques d’un séisme cible suffisamment variés pour être représentatifs d’un grand nombre de scénarios de sources possibles et prenant en compte dans un sens statistique de potentiels effets de directivité. Cette approche a également été appliquée à la simulation d’un séisme historique pyrénéen Mw6.1. Dans une seconde partie, nous nous appuyons sur un modèle de source étendue plus complexe, combinant des modèles cinématiques de sources composites fractales avec l’approche des FGEs. Le potentiel de la méthode est testé sur une application au séisme de L’Aquila. Cela a permis de produire des résultats très satisfaisants sur l’ensemble des paramètres des mouvements du sol analysés. Cette méthode de simulation apparaît comme étant très prometteuse pour la mise en œuvre d’une méthodologie de simulation en aveugle, même si la principale difficulté réside dans la nécessité de définir la variabilité de nombreux paramètres d’entrée mal connus dans le cadre de la simulation d’un futur séisme. / One of the major scientific problems in seismology is to estimate the ground motions expected at a given site from a future earthquake. The aim of this thesis is to test and validate two different methods of ground motions simulation based on the empirical Green’s function approach and to provide elements that can help to develop a blind simulation methodology. In a first part, a simulation method based on a stochastic point source approach is validated on the real data of recent earthquakes well instrumented : the Les Saintes earthquake Mw6.4 and the L’Aquila earthquake Mw6.3. We have developed a blind simulation approach by taking into account an uncertainty on the parameter of stress drop ratio C. This approach allows to generate a set of synthetic accelerograms of a target earthquake varied enough to be representative of a large number of possible source scenario and taking into account in a statistical sense potential directivity effects. This approach is also applied to the simulation of an historical Pyrenean earthquake Mw6.1. In a second part, we use a more complex extended source model, combining kinematic models of fractal composite sources with EGF approach. The potential of the method is tested on an application to L’Aquila earthquake. This has produced very satisfying results on all ground motion parameters analyzed. This simulation method appears to be very promising for the implementation of a blind simulation methodology, even if the main difficulty lies in the need to define the variability of many poorly known input parameters in the simulation of a future earthquake.