Au cours de leur propagation, les ondes sismiques sont atténuées par deux phénomènes : l'absorption causée par les propriétés anélastiques des matériaux, d'une part, et la diffusion ou " scattering " causée par la présence d'hétérogénéités de petite échelle dans le milieu d'autre part. L'objectif de cette thèse est de cartographier les propriétés de diffusion et d'absorption des ondes sismiques dans deux contextes géophysiques extrêmes présentant des échelles spatiales très différentes. La première partie du manuscrit est consacrée à la stratification d'hétérogénéité dans la Lune. À l'aide d'un modèle original de diffusion en géométrie sphérique, nous avons inversé les mesures de temps d'arrivée du maximum d'énergie et de décroissance de la coda sismique réalisée sur les données des missions Apollo. Nos inversions mettent en évidence un très fort contraste des propriétés de scattering entre le mégarégolithe très atténuant et le manteau lunaire profond transparent. L'atténuation est très largement dominée par le scattering et suggère la présence de fracturation jusqu'à environ 100 km de profondeur, affectant ainsi le manteau. Une nouvelle méthode d'estimation de la profondeur des séismes superficiels fondée sur les signaux diffus a été développée et permet de confirmer l'existence de failles actives autour de 50 km de profondeur. La deuxième partie de la thèse est consacrée à la structure d'atténuation de Taïwan, une région qui présente des structures géologiques très variées dans un contexte tectonique de double subduction. On utilise la MLTWA (Multiple Lapse Time Window Analysis) -une méthode fondée sur le rapport entre énergie cohérente et incohérente du signal sismique- pour imager les variations latérales d'atténuation. Dans un premier temps nous avons travaillé dans l'hypothèse classique de diffusion isotrope dans un demi-espace. Nos résultats mettent en évidence un niveau d'atténuation globale très élevé ainsi que de forts contrastes des propriétés de scattering sur des échelles spatiales fines, de l'ordre de 10-20 km. La diffusion est particulièrement marquée dans les bassins de la côte ouest, le sud et la chaîne côtière associée à la collision avec l'arc volcanique de Luçon à l'est. L'absorption augmente graduellement vers l'est et atteint son maximum sous l'arc volcanique. L'examen de l'accord entre données et modèles a posteriori montre sans ambiguïté les limites de l'hypothèse de diffusion isotrope dans un demi-espace sur un ensemble de stations situées le long des côtes. Ceci nous conduit à explorer les effets de la diffusion anisotrope dans un guide d'onde modélisant la croûte. La prise en compte de l'anisotropie améliore significativement l'accord du modèle aux données. En particulier, à basse fréquence (1-2 Hz), notre étude démontre la prédominance de rétro-diffusion. Ce résultat est compatible avec la présence de forts contrastes d'impédance dans la croûte et suggère la présence massive de fluides dans les zones de failles et de volcans à Taïwan. La mesure de l'anisotropie de la diffusion ouvre des perspectives nouvelles de caractérisation des hétérogénéités géophysiques de petite échelle. / During their propagation, seismic waves are attenuated by two phenomena: on one hand, absorption caused by the anelastic properties of the materials, and on the other hand, scattering caused by the presence of small-scale heterogeneities in the medium. The aim of this thesis is to map the properties of scattering and absorption of seismic waves in two extreme geophysical contexts with very different spatial scales. The first part of this memoir is devoted to the stratification of heterogeneities in the Moon. We use a new diffusion model in spherical geometry to invert measurements of the time of arrival of the maximum of energy and the seismic coda decay on data from the Apollo missions. Our inversions provide evidence of a very sharp contrast of scattering properties between the highly attenuating megaregolith and the transparent deep lunar mantle. Attenuation is largerly dominated by scattering and suggests the presence of fractures down to about 100 km depth, into the mantle. A new method for estimating the depth of shallow moonquakes based on diffusive signals was developped and confirms the existence of active faults around 50 km deep. The second part of this thesis is devoted to the attenuation structure of Taiwan, a region with a wide variety of geological structures in the context of two subduction zones. We use the MLTWA (Multiple Lapse Time Window Analysis) -a method based on the ratio between the coherent and incoherent energy of the seismic signal- to image the lateral variations of attenuation. We worked first with the classical hypothesis of isotropic scattering in a half-space. Our results provide evidence for a globally high level of attenuation with sharp contrasts of scattering properties across small spatial scales, of the order of 10-20 km. Scattering is particularly strong in the basins of the west coast, southern Taiwan and the eastern Coastal Range associated with the collision with the Luzon volcanic arc. Absorption increases gradually eastwards and reaches a maximum below the volcanic arc. A posteriori examination of the fit between data and model shows unambiguously the limits of the hypothesis of isotropic scattering in a half-space for a number of stations located along the coasts. This leads us to explore the effects of anisotropic scattering in a guide for seismic waves representing the crust. Taking anisotropy into account significantly improves the fitness of the model to the data. In particular, at low frequency (1-2 Hz), our study shows the prevalence of backscattering. This result is compatible with the presence of sharp contrasts of impedance in the crust and suggests the strong presence of fluids in fault zones and volcanoes in Taiwan. The measurement of scattering anisotropy opens new perspectives for characterizing small-scale geophysical heterogeneities.

Dans les milieux fortement hétérogènes, les ondes ne se propagent pas de façon balistique. Elles peuvent interagir de nombreuses fois avec les hétérogénéités du milieu et entrer ainsi dans le régime de diffusion multiple. Dans ce régime, les méthodes classiques d'imagerie basées sur les trajets des ondes directes ou simplement diffusées sont inefficaces. Les formes d'ondes multiplement diffusées (coda) sont trop complexes pour être modélisées exactement mais elles sont parfaitement reproductibles et très sensibles aux variations du milieu de propagation. Des travaux récents ont démontré la possibilité de mesurer de faibles changements de vitesse d'un milieu grâce aux ondes diffuses, à l'échelle de la croûte terrestre (coda sismique) comme à l'échelle des matériaux (coda ultrasonore). Ces travaux s'intéressent majoritairement à des changements globaux ou régionaux des différents milieux. La problématique de cette thèse concerne la possibilité d'utiliser la coda pour étudier des changements locaux du milieu. Deux études complémentaires sont développées : Le problème direct consiste à modéliser les variations de la coda engendrées par un changement local. Nous distinguons le cas d'un changement local de structure (fort contraste d'impédance) du cas d'un changement local de vitesse (faible contraste d'impédance). Le problème inverse consiste à utiliser les mesures de variations de la coda pour tenter de localiser et de caractériser les changements survenus. Les applications potentielles de ces travaux concernent entre autres le suivi temporel de structures géologiques ainsi que le contrôle non destructif de matériaux hétérogènes. Avec cet objectif, les différentes méthodes développées sont illustrées par des simulations numériques d'ondes acoustiques et sismiques ainsi que par des expériences en ultrasons dans des éléments en béton. / In highly heterogeneous media, waves don't propagate ballistically. They can interact several times with the heterogeneities of the medium and enter the multiple scattering regime. In this regime, classical imaging techniques, based on direct or singly scattered waves fail. Multiply scattered waveforms (coda) are too complex for being exactly modeled but are perfectly reproducible and very sensitive to small variations of the medium. Recent works demonstrated the possibility of measuring small velocity variations with diffuse waves, either at the geophysical scale (seismic coda) or at the material scale (ultrasonic coda). These works are mainly focused in monitoring global or regional changes of the medium. The present thesis deals with the possibility of using coda waves to study local changes of the medium. Two complementary studies are developed: The forward problem addresses the modeling of the coda variations generated by a local change. We distinguish the case of a structural change (strong impedance contrast) from the case of a velocity change (small impedance contrast). The inverse problem consists in using the coda variations measurements to locate and characterize the changes that occurred. Potential applications may concern, among others, monitoring of geological structures and non-destructive testing of heterogeneous materials. This in mind, we illustrate the different studies with numerical simulations of acoustic and seismic waves and with ultrasound experiments in concrete blocks.

Durant mes trois années de thèse, j'ai été amenée à travailler sur différents aspects de la surveillance des propriétés élastiques de la croûte, à la fois par analyses numériques, mais aussi par des applications d'utilisation du bruit ambiant. Ma thèse s'articule autour de deux parties principales: Les propriétés des ondes de la coda Le libre parcours moyen est un paramètre crucial rencontré continuellement dans les différentes parties de mon travail. Dans cette partie, je présente une nouvelle façon de déterminer ce libre parcours moyen à partir des statistiques de phase. Cette méthode a été testée avec succès dans l'étude d'un volcan situé en Auvergne (France). Je présente ensuite une analyse numérique de la sensibilité que les ondes de la coda manifestent en fonction de la profondeur. Ce travail nous a permis de relier cette sensibilité à la profondeur observée dans les ondes de la coda, à une combinaison de la sensibilité des ondes de volume et de celle des ondes de surface. En effet, cette sensibilité des ondes de volume et de surface dépend directement du temps considéré dans la coda et du libre parcours moyen du milieu étudié. Nous avons été capable de montrer que le changement de vitesse relatif dans la coda était lié à une dépendance en temps. Cette importante observation nous permet de pouvoir établir une distinction entre un changement qui se produit en surface et un changement ayant lieu en profondeur. Localisation des changements dans un milieu diffusif Nous avons développé une méthode d'inversion basée sur des approches probabilistes de la propagation des ondes, afin de pouvoir localiser les changements dans le milieu. Nous avons également étudié la décohérence de la forme d'onde, ce qui constitue un aspect additionnel des techniques de surveillance du bruit sismique, qui traditionnellement sont basés sur l'évaluation du temps de retard dans la coda. Au cours de cette thèse, nous avons affiné notre méthode d'inversion en l'appliquant à trois cas d'études. Dans un premier cas, nous avons étudié les changements ayant eu lieu avant et pendant l'éruption du volcan du Piton de la Fournaise situé sur l'Ile de la Réunion. Le challenge ici est de parvenir à localiser correctement la prochaine éruption. La seconde application a concerné le séisme de Mw7,9 de Wenchuan (Chine), sur lequel nous avons obtenu de nombreuses données. Dans ce cas, nous avons pris en compte l'évolution de la coda au cours du temps et nous avons conjointement inversé les données à différents temps dans la coda pour étudier les changements induits dans la croûte, avant et pendant le séisme. A partir de ces résultats, nous avons pu clairement voir que la décohérence de la forme d'onde et les variations de vitesse n'étaient pas sensibles aux mêmes propriétés physiques. Dans le troisième cas d'étude, nous avons testé la procédure d'inversion avec un noyau 3D pour étudier la fracturation dans un bloc de béton soumis à une contrainte croissante. / During my thesis, I worked on different aspects of monitoring the elastic properties of the crust, with both numerical analysis and applications with ambient noise. The main body of my thesis consists of two main parts: 1. Properties of coda waves A very important parameter that we continuously encounter in the different parts of my thesis work is the scattering mean free path. I present an original way to determine the scattering mean free path from phase statistics that was successfully tested on a volcano in Auvergne. Then I discuss an intensive numerical analysis of the depth sensitivity of coda waves. This work allowed us to relate the depth sensitivity of coda waves to a combination of bulk wave sensitivity and surface wave sensitivity that depends on the time in the coda and on the scattering mean free path of the medium. We were able to show a time dependence of the relative velocity change in the coda that allows us to discriminate a change that occurs at the surface from a change that occurs at depth. 2. Locating changes in multiply scattering media We developed an inversion method based on probabilistic approaches of the wave propagation to locate changes in the medium. As an additional aspect to seismic noise monitoring techniques that are based on the evaluation of time delays in the coda, we also study the waveform decoherence. Within this thesis, we apply and refine the inversion method with three case studies. We study pre-and co-eruptive changes at Piton de la Fournaise volcano in La Réunion Island. The challenge here is to correctly locate forthcoming eruptions. A second data set comes from the Mw7.9 Wenchuan earthquake in China. In this study, we take the time evolution of the coda into account and jointly invert the data at different times in the coda to study changes in the crust during and after the earthquake. From the results, we can clearly see that waveform decoherence and velocity variations are not sensitive to the same physical properties. In the third study, we test the inversion procedure with a 3D sensitivity kernel to study the fracturing of concrete blocks under increased tension.

Submitted by Simone Rizzatto Albertini Garcia (simone.rizzatto@gmail.com) on 2018-05-23T00:14:48Z No. of bitstreams: 1 Dissertação - SIMONE final 2.pdf: 4501566 bytes, checksum: 1abbddc6dd32c59519f7cf494b6172db (MD5) / Approved for entry into archive by Elza Mitiko Sato null (elzasato@ibilce.unesp.br) on 2018-05-24T12:34:29Z (GMT) No. of bitstreams: 1 garcia_sra_me_sjrp.pdf: 4351609 bytes, checksum: 2423c7ca61abd840c2a28178110ee6da (MD5) / Made available in DSpace on 2018-05-24T12:34:29Z (GMT). No. of bitstreams: 1 garcia_sra_me_sjrp.pdf: 4351609 bytes, checksum: 2423c7ca61abd840c2a28178110ee6da (MD5) Previous issue date: 2018-04-06 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nesta dissertação, o objetivo é identificar regularidades que possam ser típicos do processo de aquisição de escrita da grafia de consoantes nasais em posição de coda silábica do português brasileiro. A sílaba é considerada quanto a características fonéticas e fonológicas. Sob o aspecto fonético, a posição de coda silábica corresponde a um momento de redução de energia, o que pode tornar os segmentos que preenchem essa posição da sílaba menos audíveis. Sob o aspecto fonológico, a coda é um constituinte não-imediato da sílaba que apresenta várias restrições quanto ao seu preenchimento. A nasalidade apresenta uma complexidade decorrente de aspectos fonéticos aliados a uma discussão na literatura a respeito de sua representação fonológica. Soma-se, ainda, o fato de a nasal em coda no português brasileiro apresentar, sob o aspecto gráfico, três possibilidades de registro ortográfico (<m>, <n> e <~>). O córpus é constituído de grafias de palavras produzidas em ambiente escolar por alunos do primeiro ano do Ensino Fundamental em uma escola privada do noroeste paulista. As grafias de coda foram identificadas a partir de dezessete propostas de escrita, incluindo listas, músicas, parlendas, trava-língua, receita culinária, propostas de listas a partir de imagens. A metodologia consiste de análise quantitativa e qualitativa das grafias de coda. Os dados foram organizados de acordo com (i) registro de sílabas CVC/VC/CCVC com codas consonantais <S, L, R, N>, (ii) não registro de sílaba com coda nasal, (iii) registro não-convencional de rima com coda nasal, (iv) registro convencional de coda nasal. Esses registros foram analisados segundo os seguintes critérios linguísticos: vogal no núcleo silábico; posição da sílaba dentro da palavra; tonicidade da sílaba; número de sílabas da palavra e registro ortográfico. Foi observada a tendência de a grafia do segmento em coda nasal ser o último a ser registrado em comparação com os outros segmentos consonantais nessa mesma posição silábica, quando consideradas produções escritas ao longo do primeiro ano do Ensino Fundamental. Ao final do primeiro ano letivo, os sujeitos analisados flutuavam entre grafar e não grafar convencionalmente a coda nasal (como “aveca”, “avenca”), evidenciando a aquisição da sílaba com coda nasal, embora ainda não tendo dominado a convenção ortográfica do registro da nasalidade distintiva (“quen”). As grafias não-convencionais encontradas nos dados levantados podem ser explicadas a partir do trânsito do sujeito escrevente por práticas orais e letradas, uma vez que, em sua produção escrita, os sujeitos ancoram-se em características fonético-fonológicas dos enunciados falados e, também, em características ortográficas dos enunciados escritos. / The goal of the present dissertation is to identify patterns that may be typical of the acquisition process of writing the spelling of nasal consonants in syllable coda position of Brazilian Portuguese. The syllable takes into consideration both phonetic and phonological features. Under the phonetic aspect, the syllable coda position corresponds to a moment of energy reduction, which can make the segments that fill this position of the syllable less audible. Under the phonological aspect, the coda is a non-immediate constituent of the syllable that has many restrictions on your filling. The nasality presents a complexity due to phonetic aspects combined with a discussion in the literature about its phonological representation. This also happens due to the fact that the coda in Brazilian Portuguese nasal presents, under the graphic aspect, three possibilities of Registry Checker (<m>, <n> and <~>). The córpus consists of spellings of words produced in schools for students of the first year of elementary school in a private school in the Northwest of São Paulo. The spellings of coda were identified from seventeen written proposals, including lists, songs, nursery rhymes, tongue twisters, cooking recipes, lists proposals from images. The methodology consists of quantitative and qualitative analysis of the spellings of coda. The data was organized according to (i) record of syllables CVC/VC/ CCVC with consonant codas < S, L, R, N >, (ii) no record of syllables with nasal coda, (iii) non-conventional record rhymes with nasal coda, (iv) conventional record nasal coda. These records were analyzed according to the following criteria: linguistic vowel in the syllable nucleus; syllable position within the word; the tone syllable; number of syllables of the word and spelling record. It was observed the likelihood of the spelling of the segment in nasal coda to be the last to be recorded in comparison with the other consonantal segments on the same syllabic position, when considered written productions throughout the first year of elementary school. At the end of the first academic year, the subjects examined floated between carve and carve not conventionally the nasal coda (as "aveca", "avenca"), evidencing the acquisition of syllables with nasal coda, although not yet having mastered the orthographic Convention of record of distinctive nasality ("quen"). The unconventional spellings found in the data collected can be explained from the subject's transit clerk for oral and literate practices, since in your written work, the subject anchor-quality features-phonetic utterances spoken of phonological and orthographic features of written statements.

Resumo: Propusemos neste trabalho uma investigação a respeito da grafia da coda silábica simples por alunos da Educação de Jovens e Adultos (EJA), a partir do registro e do não-registro gráfico de elementos consonantais nessa posição silábica, discutindo, particularmente, a não-convenção ortográfica. Focalizamos aqueles registros que alteram a estrutura da sílaba alvo de nosso estudo: o registro não-convencional da coda consonantal silábica simples, abrangendo casos de troca entre consoantes e entre consoante e vogal. Objetivamos, deste modo, descrever o modo pelo qual os alfabetizandos de um programa de Educação de Jovens e Adultos registram, ou não, em sua escrita a posição de coda de sílabas constituídas de um segmento consonantal (/l/, /N/, /R/, e /S/). Partimos da concepção da sílaba fundamentada na teoria métrica da sílaba (SELKIRK, 1982), como também da análise da sílaba proposta por Bisol (1999). Para realizar a pesquisa, foram utilizados dados de escrita dos alfabetizandos da EJA do Termo II de escolarização, o que corresponde aos terceiro e quarto anos do Ensino Fundamental. Realizamos a coleta da escrita de palavras contendo a estrutura silábica de coda simples preenchida por /l, N, /R/ e /S/, a partir de 5 propostas textuais. Nos resultados, observamos que os alfabetizandos mostram-se "sensibilizados" ao preenchimento da posição da coda silábica de modo a registrá-la em sua escrita de acordo com as convenções ortográficas, em grande parte de seus registros: coda vibrante apresentou maior porcentagem de registro convencional (/R/ = 80,37%), seguida da coda fricativa (/S/ = 77%), da coda nasal (/N/ = 65%) e, por fim, da coda lateral (/l/ = 55%). Em relação aos registros não-convencionais, observamos que os alunos jovens e adultos, na grande maioria... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work we propose an investigation about the spelling of the simple syllable coda by students from the program Young and Adult Education. We start from the graphic and from the non-graphic register of the consonantal elements in this syllabic position and we discuss particularly the orthographic non-convention. We focus on the registers that modify the structure of the target syllable in our work: the non-conventional register of the simple consonantal syllable coda and we cover exchange cases in consonants and between the consonant and the vowel. Thus we aim to describe the way the students of the Program of Young and Adult Education register, or not, in their writings the position of the syllabic coda constituted by a consonantal segment (/l/, /N/, /R/, and /S/). We start from the conception of the syllable based on the metric theory of the syllable (SELKIRK, 1982), as well the analysis of the syllable proposed by Bisol (1999). To accomplish this research, we used data from the writing of the students of the second term of schooling in the Young and Adult Education, it corresponds to the third and fourth year of the basic education. We collected the writing of words that contained the simple syllabic structure of the coda filled with /l/, /N/, /R/, and /S/ from five textual proposals. In the outcomes, we observed that the students were "sensitized" to the filling of the position of the syllabic coda by registering their writing according to the orthographic convention in most of their registers: vibrant code presented a greater percentage of conventional register (/R/ = 80,37%), followed by the fricative code (/S/ = 77%), nasal coda (/N/ = 65%), and finally, the lateral coda (/l/ = 55%). In regards to the non-conventional registers, we observed that the young and adult students... (Complete abstract click electronic access below) / Orientador: Larissa Cristiana Berti / Coorientador: Luciani Ester Tenani / Banca: Cristiane Carneiro Capristano / Banca: Lourenço Jurado Chacon / Mestre

Frequency-dependent earthquake coda attenuation values are often reported; however such measurements usually depend on the types of the attenuation models employed. In this thesis, I use numerical modeling of Peaceful Nuclear Explosion (PNE) codas at far regional to teleseismic distances to compare two of such models, namely the conventional frequency-dependent attenuation with parameters (Q0, ¦Ç) defined by Qcoda(f) = Q0f¦Ç and frequency-independent effective attenuation (Qe) with geometrical attenuation (¦Ã). The results favour strongly the (¦Ã, Qe) model and illustrate the mechanisms leading to apparent Qcoda(f) dependencies. Tests for variations of the crustal velocity structures show that the values of ¦Ã are stable and related to lithospheric structural types, and the inverted Qe values can be systematically mapped into the true Swave attenuation factors within the crust. Modeling also shows that ¦Ã could increase in areas where relatively thin attenuating layers are present within the crust; such areas could likely be related to younger and active tectonics. By contrast, when interpreted by using the traditional (Q0,¦Ç) approach, the synthetic coda shows a strong and spurious frequency dependence with ¦Ç ¡Ö 0.5, which is also similar to many published observations.<p> Observed Lg codas from two Peaceful Nuclear Explosions located in different areas in Russia show similar values of ¦Ã ¡Ö 0.75¡¤10-2 s-1, which are also remarkably close to the independent numerical predictions in this thesis. At the same time, coda Qe values vary strongly, from 850 in the East European Platform to 2500 within the Siberian Craton. This suggests that parameters ¦Ã and Qe could provide stable and transportable discriminants for differentiating between the lithospheric tectonic types and ages, and also for seismic coda regionalization in nuclear-test monitoring research.

Este estudio recoge los principales resultados del trabajo sobre modelización de la anelasticidad en la Península Ibérica a partir de ondas de Coda correspondientes a una selección de 935 registros sísmicos digitales registrados en 27 estaciones equipadas con instrumental de corto periodo y pertenecientes al Instituto Geográfico Nacional (IGN). Tras la selección, se ha aplicado sistemáticamente la corrección por respuesta instrumental sobre todas las señales a analizar. Los sismos disponibles para este estudio ocurrieron en el intervalo 1997-1999 y se sitúan en las siguientes tres áreas en las que se concentra la sismicidad natural de la Península Ibérica: El Noroeste Peninsular (Galicia); El Noreste Peninsular (Cataluña, Aragón, Navarra y, parcialmente, el sur de Francia); El Sur Peninsular (sur de Valencia, Murcia, Andalucía y, parcialmente, el sureste de Portugal).Mediante métodos basados en la dispersión simple se ha calculado el factor Q de coda y su dependencia frecuencial en todas las estaciones en el rango frecuencial comprendido entre 1.5 Hz y 9.0 Hz. La variación lateral de Q de coda se resume en los mapas de iso-Q correspondientes a la banda frecuencial 6.0-8.0 Hz. Esta banda frecuencial se sitúa en la parte central del ancho de banda de las estaciones empleadas. Los mapas de iso-Q a 7 Hz han permitido detectar anomalías de Qc relacionadas con características geotectónicas de cada región. En general se obtienen valores de Qc relativamente bajos en las tres regiones estudiadas. Estos valores son ligeramente más altos en la zona noroeste y más bajos en la zona sur. También se han ajustado a la ley de dependencia frecuencial Q = Q0 &#1468; f &#957;, los valores obtenidos para el factor Qc a distintas frecuencias, obteniéndose, en general, valores de Qc0 bajos y exponentes &#957; altos. A raíz de los resultados obtenidos en este estudio, se advierte que la ley de dependencia frecuencial utilizada, y normalmente empleada para analizar la variación de los parámetros de atenuación inelástica, intrínseca y dispersiva, resulta no ser adecuada cuando se analiza una banda frecuencial amplia.Un segundo aspecto analizado en este trabajo es la variación temporal de los parámetros de atenuación. La ocurrencia de dos sismos de intensidad VII, uno en el Sur y otro en el Noroeste Peninsular, ha permitido analizar esta variación temporal utilizando sismos anteriores y posteriores a las crisis sísmicas de Mula en el Sur (Febrero de 1999) y de Lugo en el Noroeste (Mayo de 1997). Como consecuencia de este análisis, los resultados apuntan variaciones significativas de Qc antes y después del sismo principal.La aplicación sistemática del método de ventanas temporales múltiples que tiene en cuenta la dispersión múltiple y permite separar la atenuación intrínseca y dispersiva, ha permitido confirmar aspectos tradicionalmente aceptados y avanzar en otros en los que existe una controversia importante como son, la relación entre la Q de coda y la Q total, intrínseca y dispersiva y la dependencia frecuencial de todas ellas. Los resultados obtenidos con este análisis permiten afirmar que la atenuación intrínseca domina sobre la dispersiva para altas frecuencias en todas las regiones analizadas. En cambio, para frecuencias bajas, inferiores a 3Hz, la atenuación dispersiva domina en la región sur. / In the present study we analyze the anelastic structure of the Iberian Peninsula by using seismic coda waves of local and regional earthquakes. We use digital data collected at the seismic network of the Spanish Geographic Institute (Instituto Geográfico Nacional, IGN). Our data reflect the natural seismicity of the Iberian Peninsula and lead to consider and analyze three separated regions with different geotectonic features: The Northwestern (NO), the Northeastern (NE) and the Southern (S) Iberian Peninsula.We have analyzed 935 high quality seismograms recorded at 27 stations, equipped with digital short period and some broadband instruments, in order to observe the Qc quality factor and its frequency dependence in the frequency range between 1 and 10 Hz. The best resolution has been obtained for frequencies between 6.0 and 9.0 Hz. This frequency band, which in most cases is the center frequency of the instrument response, has been used to plot iso-Q7Hz maps for the three studied regions. The iso-Q maps at 7 Hz show a good agreement with the main geotectonic characteristics of the mapped areas. Relatively low Qc values are found in the three regions, but Qc values are higher in the NO region and lower in the S region.The frequency dependence of the quality factor has been also analyzed by using the well known law Q = Q0 &#61655; f&#61550;. We obtain low Qc0 values and high &#61550;. It is noted that probably the law mentioned before, which is mostly used in attenuation studies, is not adequate when a relatively broad frequency band is involved.We have used two seismic events occurred in the NE region and in the S region to analyze the time dependence of the quality factor. The seismic intensity of both main earthquakes was VII in the MSK scale. We have analyzed events occurred before and after the main shock occurred during the seismic crisis of Mula in the Southeastern Iberian Peninsula (February, 1999), and the same procedure was used with events associated with the seismic crisis of Lugo, in the Northwestern Iberian Peninsula (May, 1997). Our results seems indicate temporal differences before and after the main shocks in both seismic crisis.The application of the multiple lapse time window analysis (MLTWA), which takes into account the multiple scattering and leads to the separation of the intrinsic and scattering attenuation, confirms most of the results published but also gives some indications to go further in some subjects, as the relation between coda Q (Qc), intrinsic Q (Qi), scattering Q (Qs) and total Q (Qt) and their frequency dependence. The final results indicate that the intrinsic attenuation is more important that the scattering attenuation at high frequencies in all three analyzed regions. In the southern region and for low frequencies, lower than 3 Hz, the scattering loss is the main attenuation mechanism.

Frequency-dependent earthquake coda attenuation values are often reported; however such measurements usually depend on the types of the attenuation models employed. In this thesis, I use numerical modeling of Peaceful Nuclear Explosion (PNE) codas at far regional to teleseismic distances to compare two of such models, namely the conventional frequency-dependent attenuation with parameters (Q0, ¦Ç) defined by Qcoda(f) = Q0f¦Ç and frequency-independent effective attenuation (Qe) with geometrical attenuation (¦Ã). The results favour strongly the (¦Ã, Qe) model and illustrate the mechanisms leading to apparent Qcoda(f) dependencies. Tests for variations of the crustal velocity structures show that the values of ¦Ã are stable and related to lithospheric structural types, and the inverted Qe values can be systematically mapped into the true Swave attenuation factors within the crust. Modeling also shows that ¦Ã could increase in areas where relatively thin attenuating layers are present within the crust; such areas could likely be related to younger and active tectonics. By contrast, when interpreted by using the traditional (Q0,¦Ç) approach, the synthetic coda shows a strong and spurious frequency dependence with ¦Ç ¡Ö 0.5, which is also similar to many published observations.<p> Observed Lg codas from two Peaceful Nuclear Explosions located in different areas in Russia show similar values of ¦Ã ¡Ö 0.75¡¤10-2 s-1, which are also remarkably close to the independent numerical predictions in this thesis. At the same time, coda Qe values vary strongly, from 850 in the East European Platform to 2500 within the Siberian Craton. This suggests that parameters ¦Ã and Qe could provide stable and transportable discriminants for differentiating between the lithospheric tectonic types and ages, and also for seismic coda regionalization in nuclear-test monitoring research.

The prevalence of concrete and cement-based materials in the civil infrastructure plus the risk of failure makes structural health monitoring an important issue in the understanding of the complete life cycle of civil structures. Correspondingly, the field of nondestructive evaluation (NDE) has been maturing and now concentrates on the detection of flaws and defects, as well as material damage in early stages of degradation. This defect detection is typically usually done by looking at the impulse response of the medium in question such as a cement-based material. The impulse response of a solid can be used to image a complex medium. Classically, the waveform is obtained by an active setup: an ultrasonic signal is generated at one location and recorded at another location. The waveform obtained from imaging can be used to quantitatively characterize the medium, for example by calculating the material's diffusivity coefficient or dissipation rate. In recent years, a different monitoring technique has been developed in seismology to measure the velocity of different kinds of waves, the Coda Wave Interferometry (CWI). In this CWI technique, the main focus is given to the late part of the recorded waveform, the coda. CWI is now successfully used in seismology and acoustics. In the current research, CWI is applied on concrete in different damage states to develop basic knowledge of the behavior of the wave velocity, and how it can be used to characterize cement-based materials. By comparing two impulse responses, the relative velocity change between the two impulse responses is used to characterize damage. Because of the stress-dependency of the velocity change, the calculations can also be used to directly calculate the Murnaghan's and Lam´e's coefficients. The newer technique of CWI is applied - the Stretching Technique (ST) [27]. The first goal of this research is to establish the viability of using CWI in cement-based materials. Next, we use the ST in the application of stress as we compress concrete samples for the detection of thermal damage, ASR-damage and mechanical softening.

No description available.