[pt] O problema de Inversão Sísmica envolve a determinação das propriedades físicas da superfície a partir de dados amostrados na superfície. A construção de um modelo matemático da resposta da subsuperfície à excitação de uma fonte sísmica, tendo como parâmetros as propriedades físicas da subsuperfície, fornece um modelo sintético desta resposta para determinados valores dos parâmetros. Isto permite comparar dados amostrados e modelos sintético. A perturbação do modelo pela variação dos seus parâmetros pode aproximar dados amostrados e sintéticos e colocar o problema da Inversão como um problema de minimização de uma função de erro que os ajuste de forma adequada. Usualmente, os métodos que tentam minimizar a medida a medida de erro supõem um comportamento linear entre a perturbação do modelo e esta medida. Na maioria dos problemas geofísicos, esta medida apresenta um alto grau de não linearidade e uma grande quantidade de mínimos locais. Isto torna estes métodos baseados em aproximações lineares muito sensíveis à escolha de uma boa solução inicial, o que nem sempre está disponível. Como resolver este problema sem uma boa solução inicial? A teoria da Inferência Bayesiana oferece uma solução pelo uso de informação a priori sob o espaço dos parâmetros. O problema de Inversão volta então a ser um problema de otimização onde se precisa maximizar a probabilidade a posteriori dos parâmetros assumirem um certo valor dado que se obteve o resultado da amostragem dos dados. Este problema é resolvido pelo método do Simulated Annealing (SA), método de otimização global que faz uma busca aleatória direcionada no espaço de solução. Este método foi proposto por uma analogia entre o recozimento física de sólidos e problemas de otimização. O SA, na sua variante Very Fast Simulated Annealing (VFSA), é aplicado na solução de problemas de Inversão Sísmica 1 D para modelos acústico e elásticos gerados sinteticamente. A avaliação do desempenho do SA usando medidas de erro com diferentes normas é realizada para um modelo elástico adicionado de ruído aleatório. / [en] The seismic inverse problem involves determining the subsurface physical properties from data sampled at Earth`s surface. A mathematical model of the response of the subsurface excited by a seismic source, having physical properties as parameters, provides a synthetic model for this response. This makes possible to compare sampled and synthetic data. The perturbation in the model due to the variation of its parameters can approximate these data and states the inversion problem as the minimization of an error function that fits them adequately. Usually, the methods which attempt to minimize this error assume that a perturbation in the model is linearly relates with a perturbation in the measured response. Most geophysical inverse problems are highly nonlinear and are rife with local minima. Therefore these methods are very sensitive to the choice of the initial model and good starting solutions may not be available. What should be done, if there is no basis for an initial guess? The theory of Bayesian inference provides an answer to this question taking into account the prior information about the parameter space. The inverse problem can then be stated as an optimization problem whose goal is to maximize the posterior probability that the set of parameters has a certain value once given the result of the sample. This problem is solved by the Simulated Annealing method, a global optimization method that executes a oriented random search in the solution space. This method comes from an analogy between the physical annealing of solids and optimization problems. The Very Fast Simulated Annealing (VFSA), a variant of SA, is applied to the solution of 1 D seismic inverse problems generated synthetically by acoustic and alastic done by a elastic model with additive noise.

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Seismic isolation systems are widely recognized as beneficial for protecting both acceleration- and displacement-sensitive nonstructural systems and components. Furthermore, adaptive isolation systems have been shown to enable engineers to achieve various performance goals under multiple hazard levels. These systems have been implemented for horizontal excitation, but there has been very limited research on isolation for vertical excitation. Thus, this paper seeks to evaluate the benefit of adaptive vertical isolation systems for component isolation, specifically for nuclear plants. To do this, three vertical isolation systems are designed to achieve multiple goals: a linear spring and a linear damper (LSLD), a linear spring and a nonlinear damper (LSND) and a nonlinear spring and a linear damper (NSLD). To investigate the effectiveness of the proposed systems, a stiff piece of equipment is considered at an elevated floor within a power plant. A set of 30 triaxial ground motions is used to investigate the seismic response of the equipment. The maximum isolation displacement and equipment acceleration are used to assess the effectiveness of the three isolation systems. While all systems significantly reduce the seismic accelerations on the equipment compared to the fixed-base case, a LSND system is shown to exhibit superior seismic performance across multiple hazard levels. / Thesis / Master of Applied Science (MASc)

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1982. / Microfiche copy available in Archives and Science / Bibliography: leaves 68-69. / by Wafik Bulind Beydoun. / M.S.

Structural fuses are ductile elements of a structure that are designed to yield and protect the surrounding members from damage, and then be replaceable after a major seismic event. A promising type of seismic structural fuse consists of a steel plate with engineered cutouts leaving a configuration of shear-acting links remaining. There have been several studies on various cutout patterns for shear-acting structural fuses including butterfly-shaped links, hourglass-shaped links, elliptical holes, and link shapes obtained from topology optimization. In most cases, the links are designed to undergo flexural yielding as it is believed to exhibit more ductility than other limit states. However, computational and experimental studies on the shear yielding limit state are limited. Additionally, the transition between shear dominated and flexural dominated limit states has not been previously investigated. Hence, a systematic and thorough study on the different limit states of these structural fuse shapes is necessary to provide better understanding on the structural behavior of each shape and accurately predict the controlling limit state during a seismic event. In addition, a previous study recognized that delaying shear buckling while promoting yielding is a way to improve the seismic performance of shear-acting structural fuses. However, the resulting new topologies were not experimentally validated. Furthermore, the computational study revealed that large localized plastic strain is one major challenge for these optimized configurations which might lead to potential for fracture. With the goals of filling the gaps in previous research, a computational and experimental program was conducted to (1) understand seismic performance of five structural fuse shapes, (2) develop a new ductile structural fuse shape with both buckling and fracture resistance, and (3) create design guidelines for practical design. This study consisted of the following parts (a) Creation of a new structural fuse shape called the Tied Butterfly Shape, (b) An experimental program with 20 specimens categorized into five groups including the shape created using topology optimization to resist buckling, the new shape called Tied Butterfly Shape, the butterfly shape, the hourglass shape and the elliptical holes, (c) Use of finite element models to better understand and interpret test data, (d) Two computational parametric studies conducted to investigate the effect of geometrical parameters on structural behavior of the optimized shape and Tied Butterfly Shape, (e) Development of design recommendations for each structural fuse shape. The computational and experimental results reported in this dissertation demonstrate that these structural fuse shapes are capable of improving the seismic performance of buildings. The presented design recommendations allow designers and researchers to continue exploring these structural fuse shapes. / Doctor of Philosophy / Structural fuses are ductile elements of a structure that are designed to yield and protect the surrounding members from damage, and then be replaceable after a major seismic event. Several studies on various cutout patterns for shear-acting structural fuses including butterfly-shaped links, hourglass-shaped links, elliptical holes, and link shapes obtained from topology optimization, reported that they offer several advantages for use in structural systems. Nevertheless, systematic studies on key limit states of these structural fuse shapes are limited. In addition, some analytical results have not been validated by experiments. The research work provides a comprehensive study on these structural fuse shapes. First, generalized design equations are derived using plastic mechanism analysis and key limit states of these structural fuse shapes are investigated. Second, an experimental program was conducted to further understand the cyclic behavior of these shapes associated with each limit state (i.e flexural yielding, shear yielding, lateral torsional buckling, transition between the flexural and shear yielding limit states). Then, nonlinear finite element modeling was implemented to validate against experimental results and provide better understanding of the behavior of the specimens which is not obvious during the test. Lastly, design recommendations are developed for each structural fuse shape.

Marginal zones of salt diapirs and canopies are complex geological environments, with rapid spatial variations in lithology, strain, and fluid-assisted alteration. These complex zones can contain economically attractive hydrocarbon accumulations. However, they are difficult to image seismically due to the irregular geometry of salt bodies and the large property contrast between salt and the surrounding sediments. I present an integrated and multiscale approach to build realistic models of salt margins that represent the geological heterogeneity and seismic anisotropy in such complex zones. Structural field data and petrophysical measurements are used to constrain such models. A suite of evaporite samples of various compositions are used to predict the seismic anisotropy from their crystal preferred orientations (CPOs) and elastic properties. Ultrasonic seismic velocities are measured to calculate the relative contribution of the shape preferred orientations to the seismic anisotropy of such samples. Calculation of the seismic anisotropy produced by thinly interlayered evaporites provides a link between small-scale compositional heterogeneity with large-scale seismic anisotropy. Integration of outcrop structural models, petrophysical measurements and the characterisation of seismic anisotropy of salt is possible through seismic modelling. My results suggest that the seismic anisotropy of these samples is strongly controlled by their CPOs, which ranges from 3 to 7% for halite, from 8 to 10% for anhydrite, and from 13 to 22% for gypsum. Predictions indicate that the contribution of a small amount (< 10 %) of anhydrite can moderately alter the seismic anisotropy of polycrystalline evaporite. A small amount of anhydrite interlayered with halite yields anisotropy parameters with magnitudes of = −0.014, = −0.044, and = −0.193, which agree with those parameters calculated for polycrystalline salt. Such calculations of seismic anisotropy at grain scale enable the study of the propagation of seismic waves through salt margins. Seismic images generated from outcrop models of salt diapir flanks show moderate image degradation if anisotropy of salt is neglected during seismic migration. This methodology provides a foundation for the characterisation of seismic anisotropy of salt with which models of salt margins can be improved.

The integration of seismic attributes and well data is an important step in the development of reservoir models. These models draw upon large data sets including information from well logs, production history, seismic interpretation, and depositional models. Modern integration techniques use the extensive data sets to develop precise models using complex workflows at increased cost of time and computational power. However, a gap exists in which a geostatistically driven procedure could integrate pattern statistics inferred from seismic images and those integrated from analogous geologic systems in order to develop spatially accurate reservoir models. Direct Sampling Seismic Integration Process, DSSIP, was first proposed by Henke and Srinivasan (2010) as an alternative to traditional seismic integration methods. The process provides a probabilistic mapping tool for fast reservoir analysis based on sparse conditioning data in a target reservoir and fully interpreted data from an analog field. DSSIP combines the structural information present in seismic data and facies patterns present in a training reservoir to create a fully realized output map for the target field. In this work, the basic DSSIP algorithm has been further optimized by performing a detailed parameter sensitivity study. The basic DSSIP algorithm has been demonstrated for a real field data set for a deepwater Gulf of Mexico reservoir. The basic DSSIP algorithm has also been analyzed to understand and model the effects of features such as salt canopy that can blur the seismic image. Finally, a modification to the basic algorithm is also presented that uses only a training model and the seismic data for the target reservoir in order to generate reservoir models for the target reservoir. This procedure eliminates the requirement to have a matching pair of training data sets for both the facies distribution and the corresponding seismic response. / text

The use of base isolation to help mitigate and reduce the effects of earthquake excitations has become common place on many important structures. There is also a larger amount of heavier machinery and equipment being stored in some of these important structures; this means that there is a possibility that there are mass irregularities with in a structure. While the response of structures that have been base isolated has been studied they are typically design with floors having a uniform mass. This thesis investigates how mass irregularities affect the response of the floor accelerations and interstorey drifts within a flexural structure with and without a base isolation unit. The ductility demand of the isolator unit is also investigated at during the course of the analysis. The reason for observing the response of the structure is because often in building design there is a need to have floors that have larger masses then the rest of the structure, and understanding how these mass irregularities affect the response of the structure, then the designing of such structures will be simpler during the initial concept stage.

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