xv, 108 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Studies on seismic attenuation are an important complement to those on seismic velocity, especially when interpreting results in terms of temperature. But estimation of attenuation (t*) is more computationally involved and prone to contamination by noise, especially signal-generated noise. We have examined the effects of various forms of synthetic noise on t* estimation using time and frequency domain methods with varying window lengths and data frames of reference. We find that for S-waves, error due to noise can be reduced by rotating the data into the estimated polarization direction of the signal, but unless the exact nature of the noise is known, no method or window size is clearly preferable. We recommend the use of multiple estimation methods including a careful assessment of the uncertainty associated with each estimate, which is used as a weight during inversion for 1/Q. Our synthetic tests demonstrate that the misfit between actual and estimate-predicted traces or spectra correlates with t* error, and a similar relationship is suggested for real data. Applying this approach to data from the Yellowstone Intermountain Seismic Array, we employ two important constraints during inversion. First, we scale the misfit values so that the resulting weights are comparable in magnitude to the squares of the eventual data residuals. Second, we smooth the model so that the maximum attenuation (1/Q) does not exceed a value which would totally explain the observed velocity anomaly. The tomographic models from all the estimation methods are similar, but in the vicinity of the Yellowstone mantle plume, S-wave models show greater attenuation than do P-wave models. We attribute this difference to greater focusing by the plume of S-waves. All models show relatively high attenuation for the plume at depth, but above 250 km attenuation in the plume drops rapidly to values less than those of the surrounding mantle. We attribute this drop to the onset of partial melting, which dehydrates the olivine crystals, suppressing dislocation mobility and thereby attenuation. These attenuation models suggest excess plume temperatures at depth which are too low to support a plume origin in the lower mantle. This dissertation includes unpublished co-authored material. / Committee in charge: Eugene Humphreys, Chairperson, Geological Sciences; Emilie Hooft Toomey, Member, Geological Sciences; Douglas Toomey, Member, Geological Sciences; James Isenberg, Outside Member, Mathematics

Although much progress has been made in determining the three dimensional distribution of seismic wave velocities in the Earth, substantially less is known about the three dimensional distribution of intrinsic attenuation. In this study variations in attenuation and shear velocity of the Earth's mantle are constrained using measurements of differential travel time and attenuation. The data are broadband displacement SH seismograms filtered to have energy in the period range 8 to 20 s. Broadband data are used as they should allow a more accurate estimation of body wave attenuation to be made. The seismograms are obtained from over 600 globally distributed earthquakes of magnitude, Mw, 5.5 or greater. Two new methods for determining differential travel times and differential t* values from multiple S phases are presented. The first of these, referred to as the "waveform fitting method" is used to analyse approximately 4300 SS and S waveforms and around 1000 SSS and SS waveforms resulting in differential SS-S and SSS-SS travel times, and corresponding values of differential attenuation represented by t*. The second method, referred to as the "spectral ratio method" is used to analyse approximately 3200 SS and S and around 900 SSS and SS waveforms. The differential travel times and t* values are inverted to obtain models of the lateral variation of shear velocity and lateral variation of q(mu) where q(mu) =1/Q(mu). The models explain the data well but have limited depth resolution. The velocity models show good correlation with previous studies, in particular, low velocities are observed underlying spreading ridges and convergent margins and high velocities are observed under continental regions. The q(mu) model shows shield regions to be less attenuating than PREM, with ridges appearing as highly attenuating features. Models of shear velocity and attenuation are also obtained by combining the body wave dataset of this study with the surface wave datasets of Van Heijst (1997) and Selby (1998).

Esta pesquisa está baseada na execução de duas linhas de refração sísmica profunda de 300 km de extensão (L1-Porangatu e L2-Cavalcante) atravessando de oeste para leste o setor central da Província Tocantins, utilizando em cada linha 120 sismógrafos digitais e explosões com tempo controlado e cargas entre 500 e 1000 kg de explosivos a cada 50 km; foram utilizados receptores GPS para o controle da hora e das coordenadas geográficas dos pontos de registro e de explosões. Esse tipo de experimento, com essas condições é pioneiro no Brasil. Os dados deste experimento, considerados de boa qualidade, permitiram, inicialmente, a elaboração de modelos 1D, para cada tiro, utilizando o programa TTInvers. Estes modelos foram relacionados sucessivamente para representar camadas com características semelhantes em um modelo preliminar para modelagem em 2D, que foi realizada com o programa MacRay. Os modelos 2D obtidos representam o resultado final da distribuição de velocidades sísmicas da crosta sob essas linhas. Estes resultados mostram a crosta sob o setor central da Província Tocantins com espessura variando entre 36 e 43 km, cujos parâmetros estão correlacionados com as principais estruturas geológicas existentes na superfície. Os valores médios de VP e da razão VP/VS na Província Tocantins variam em torno de 6,5 km/s e 1,74, respectivamente, com exceção da faixa de dobras e empurrões cujos valores são 6,3 km/s e 1,73. Sob o Cráton São Francisco esses valores são 6,8 km/s e 1,74. Existem indícios de ter ocorrido uma dupla subducção na Província Tocantins, na porção oriental, com o Cráton São Francisco subduzindo para oeste (em | 760 Ma) e na porção ocidental, com o Cráton Amazônico subduzindo para leste (em | 620 Ma). O modelo gravimétrico, obtido neste trabalho em função do modelo sísmico, se ajusta adequadamente com os dados gravimétricos observados, utilizando densidades teóricas ligeiramente modificadas, dentro dos limites permitidos pela função utilizada para calcular essas densidades com base nos valores de VP deste trabalho. As densidades do manto adotadas para a modelagem levaram em conta as idades Paleoproterozóica, sob o Cráton SãoFrancisco menos denso (3,31 g/cm3) e com maior VP (8,26 km/s), e Neoprotorozóica, sob a Província Tocantins, mais densa (3,34 g/cm3) e com menor VP (8,07 km/s). / This research is based on an execution of two lines of deep seismic refraction of 300 km of extension (L1-Porangatu and L2-Cavalcante), crossing over central sector of Tocantins Province from west to east by using, in each line, 120 digital seismographs and explosions with controlled time and explosive charges between 500 and 1,000 kg in each 50 km; GPS receivers were employed in order to control the time and geographical coordinates from recording and shot points. This kind of experiment under these explained conditions is pioneer in Brazil. Initially experiment data, which have been considered of good quality, allowed the elaboration of 1D models, using TTInvers program. Successive models were related to represent layers with similar characteristics in a preliminary model aiming of modelling in 2D, accomplished with MacRay program. Obtained 2D models represent the final result of seismic velocity distribution from crust beneath L1 and L2 lines. Results show crust under central section of Tocantins Province with thickness varying from 36 to 43 km, and whose parameters are correlated to main geological structures existents in surface. VP as well as VP/VS ratio mean values vary about 6.5 km/s and 1.74, respectively, with the exception of fold-and-thrust belt, whose values are 6.3 km/s and 1.73. Those values reach 6.8 km/s and 1.74 beneath São Francisco craton. There are indicia of double subduction occurred in the eastern portion of Tocantins Province with São Francisco Cráton subducting to west (in | 760 Ma), as well as in the western portion, with Amazon Cráton subducting to east (in | 620 Ma). The gravimetric model, obtained in this work in terms of seismic model, adequately adjusts with observed gravimetric data by using theoretical densities slightly modified, within limits allowed by the function employed to calculating the densities based on VP values achieved from this work. Adopted mantle densities to modelling took in consideration Paleoproterozoic age, beneath São Francisco Cráton, less dense (3.31 g/cm3), and with higher VP (8.26 km/s), as well as Neoproterozoic one, beneath Tocantins Province, denser (3.34 g/cm3), and with lower VP (8.07 km/s).

Esta pesquisa está baseada na execução de duas linhas de refração sísmica profunda de 300 km de extensão (L1-Porangatu e L2-Cavalcante) atravessando de oeste para leste o setor central da Província Tocantins, utilizando em cada linha 120 sismógrafos digitais e explosões com tempo controlado e cargas entre 500 e 1000 kg de explosivos a cada 50 km; foram utilizados receptores GPS para o controle da hora e das coordenadas geográficas dos pontos de registro e de explosões. Esse tipo de experimento, com essas condições é pioneiro no Brasil. Os dados deste experimento, considerados de boa qualidade, permitiram, inicialmente, a elaboração de modelos 1D, para cada tiro, utilizando o programa TTInvers. Estes modelos foram relacionados sucessivamente para representar camadas com características semelhantes em um modelo preliminar para modelagem em 2D, que foi realizada com o programa MacRay. Os modelos 2D obtidos representam o resultado final da distribuição de velocidades sísmicas da crosta sob essas linhas. Estes resultados mostram a crosta sob o setor central da Província Tocantins com espessura variando entre 36 e 43 km, cujos parâmetros estão correlacionados com as principais estruturas geológicas existentes na superfície. Os valores médios de VP e da razão VP/VS na Província Tocantins variam em torno de 6,5 km/s e 1,74, respectivamente, com exceção da faixa de dobras e empurrões cujos valores são 6,3 km/s e 1,73. Sob o Cráton São Francisco esses valores são 6,8 km/s e 1,74. Existem indícios de ter ocorrido uma dupla subducção na Província Tocantins, na porção oriental, com o Cráton São Francisco subduzindo para oeste (em | 760 Ma) e na porção ocidental, com o Cráton Amazônico subduzindo para leste (em | 620 Ma). O modelo gravimétrico, obtido neste trabalho em função do modelo sísmico, se ajusta adequadamente com os dados gravimétricos observados, utilizando densidades teóricas ligeiramente modificadas, dentro dos limites permitidos pela função utilizada para calcular essas densidades com base nos valores de VP deste trabalho. As densidades do manto adotadas para a modelagem levaram em conta as idades Paleoproterozóica, sob o Cráton SãoFrancisco menos denso (3,31 g/cm3) e com maior VP (8,26 km/s), e Neoprotorozóica, sob a Província Tocantins, mais densa (3,34 g/cm3) e com menor VP (8,07 km/s). / This research is based on an execution of two lines of deep seismic refraction of 300 km of extension (L1-Porangatu and L2-Cavalcante), crossing over central sector of Tocantins Province from west to east by using, in each line, 120 digital seismographs and explosions with controlled time and explosive charges between 500 and 1,000 kg in each 50 km; GPS receivers were employed in order to control the time and geographical coordinates from recording and shot points. This kind of experiment under these explained conditions is pioneer in Brazil. Initially experiment data, which have been considered of good quality, allowed the elaboration of 1D models, using TTInvers program. Successive models were related to represent layers with similar characteristics in a preliminary model aiming of modelling in 2D, accomplished with MacRay program. Obtained 2D models represent the final result of seismic velocity distribution from crust beneath L1 and L2 lines. Results show crust under central section of Tocantins Province with thickness varying from 36 to 43 km, and whose parameters are correlated to main geological structures existents in surface. VP as well as VP/VS ratio mean values vary about 6.5 km/s and 1.74, respectively, with the exception of fold-and-thrust belt, whose values are 6.3 km/s and 1.73. Those values reach 6.8 km/s and 1.74 beneath São Francisco craton. There are indicia of double subduction occurred in the eastern portion of Tocantins Province with São Francisco Cráton subducting to west (in | 760 Ma), as well as in the western portion, with Amazon Cráton subducting to east (in | 620 Ma). The gravimetric model, obtained in this work in terms of seismic model, adequately adjusts with observed gravimetric data by using theoretical densities slightly modified, within limits allowed by the function employed to calculating the densities based on VP values achieved from this work. Adopted mantle densities to modelling took in consideration Paleoproterozoic age, beneath São Francisco Cráton, less dense (3.31 g/cm3), and with higher VP (8.26 km/s), as well as Neoproterozoic one, beneath Tocantins Province, denser (3.34 g/cm3), and with lower VP (8.07 km/s).

[ES] Hoy en día, los materiales cementicios están presentes en la gran mayoría de las infraestructuras de nuestro entorno, como pueden ser el hormigón y el mortero, debido a su bajo coste y sus características mecánicas estructurales y de durabilidad. Pese a todo, estas se ven degradadas por factores externos e internos, reduciendo la viabilidad de estos con el paso del tiempo. Para inspeccionar estos materiales se han creado múltiples ensayos destructivos (ED) y ensayos no destructivos (END) que indican mediante ciertos parámetros el estado de los materiales de construcción. Dentro de los no destructivos, encontramos los ultrasonidos cuya propagación en estos materiales otorga información sobre su estado y estructura interna. Entre los múltiples ensayos ultrasónicos se encuentra la tomografía ultrasónica cuya base nace gracias a las Tomografías Computarizadas (TC): se ilumina un objeto mediante una fuente y se reciben las señales mediante los receptores. Se rota entorno al objeto bajo estudio combinando las señales mediante los algoritmos tomográficos y obteniendo una reconstrucción del objeto interno sin producirle ningún tipo de daño. No obstante, aunque para determinadas longitudes de onda podemos asumir una trayectoria de rayo recto, los ultrasonidos son ondas dispersivas que se difractan y se reflejan alejándose de esta condición de idoneidad afectando negativamente a las reconstrucciones. En esta tesis se estudia la tomografía de ultrasonidos aplicada a probetas de mortero. Para ello, previamente se realiza un estudio de los algoritmos de reconstrucción tomográfica donde se hace un recorrido por los principales algoritmos convencionales. Los transformados (FBP y DFT) cuyos resultados son excelentes en caso de que tengamos un nivel elevado de rayos y direcciones que conforman las proyecciones. Los algoritmos de redes neuronales (BPE y RBF) y métodos algebraicos (ART, CART, SART y SIRT) presentan buenos resultados en aquellas situaciones donde se tenga un bajo número de rayos y direcciones o alta presencia de ruido. Se comparan entre ellos mediante proyecciones obtenidas con señales simuladas y se obtienen los mejores resultados para el algoritmo FBP, con lo que las siguientes reconstrucciones reales se llevan a cabo con este método. La aplicación en la que se centra este trabajo consiste en la detección del frente de carbonatación en probetas cementicias. Es por ello que se diseñan diferentes casos de probetas con daño y sin daño para validar el funcionamiento de un sistema tomográfico. Se diseña y se construye el sistema hardware capaz de la toma automatizada de medidas empleando una configuración de rayos paralelos o de rayos en abanico. Además, se ha adaptado para que sea capaz de inspeccionar tanto con transductores acoplados por aire como inspeccionar el objeto en inmersión (acoplamiento por agua). Se concluye que la tomografía por inmersión ofrece una solución de compromiso entre transferencia de energía y proceso de automatización. Además se implementan dos modelos de redes neuronales entrenados mediante sinogramas simulados para posteriormente reconstruir casos reales. Todos los algoritmos y casos son evaluados tanto en calidad de reconstrucción como en prestaciones. / [CA] Avui dia, els materials cimentants són presents a la majoria de les infraestructures del nostre entorn com poden ser el formigó i el morter, donat el seu baix cost i les seues característiques mecànic estructurals i la seua durabilitat. Malgrat tot, aquestes es veuen degradades per factors externs i interns, reduint la seua viabilitat amb el pas del temps. Per inspeccionar dits materials s'han creat múltiples assajos destructius (AD) i assajos no destructius (AND) que indiquen mitjançant certs paràmetres l'estat dels materials de construcció. Dins del no destructius trobem els ultrasons, la propagació dels quals per aquests materials ens aporta informació sobre el seu estat i estructura interna. Entre els múltiples assajos ultrasònics, es troba la tomografia ultrasònica, la base de la qual neix gràcies a les Tomografies Computeritzades (TC): s'il·lumina un objecte per mitjà d'una font i es reben les senyals a través dels receptors. Es rota entorn l'objecte en estudi combinant les senyals mitjançant els algoritmes tomogràfics i obtenint una reconstrucció de l'objecte intern sense produir-li cap tipus de dany. No obstant això, i encara que per a determinades longituds d'ona podem assumir una trajectòria recta del raig, els ultrasons són ones dispersives que es difracten i reflecteixen, allunyant-se d'aquesta condició d'idoneïtat i afectant negativament les reconstruccions. En aquesta tesi s'estudia la tomografia d'ultrasons aplicada a provetes de morter. Amb aquesta finalitat, prèviament es realitza un estudi dels algoritmes de reconstrucció tomogràfica on es fa un recorregut pels principals algoritmes convencionals. Els transformats (FDB i DFT) els resultats dels quals son excel·lents en cas que tinguem un nivell elevat de raigs i direccions que conformen les projeccions. Els algoritmes de xarxes neuronals (BPE i RBF) i mètodes algebraics (ART, CART, SART i SIRT) presenten bons resultats en aquelles situacions on es tingui un baix número de raigs i direccions o una alta presència de soroll. Es comparen entre ells per mitjà de projeccions obtingudes amb senyals simulades i s'obtenen els millors resultats per a l'algoritme FBP, duent-se a terme les següents reconstruccions amb aquest mètode. L'aplicació en la que es centra aquest treball consisteix en la detecció del front de carbonatació en provetes cimentants. És per això que es dissenyen diferents casos de provetes amb desperfectes i sense desperfectes per validar el funcionament d'un sistema tomogràfic. Es dissenya i es construeix el sistema hardware capaç de la presa automatitzada de mesures emprant una configuració de raigs paral·lels o de raigs en ventall. A més, s'ha adaptat per a que sigui capaç d'inspeccionar tant amb transductors acoblats per aire com inspeccionar l'objecte en immersió (acoblament per aigua). Es conclou que la tomografia per immersió ofereix una solució de compromís entre la transferència d'energia i el procés d'automatització. A més s'implenten dos models de xarxes neuronals entrenats per mitjà de sinogrames simulats per a posteriorment reconstruir casos reals. Tots els algoritmes i casos són avaluats tant en qualitat de reconstrucció com en prestacions. / [EN] Nowadays, cementitious materials are present in the great majority of our surrounding infrastructures such as concrete and mortar, due to its low cost mechanic-structural features and its lasting. Nevertheless, this characteristics are degraded because of external and internal factors, reducing its viability over time. In order to inspect this materials, multiple destructive testing (DT) and non-destructive testing (NDT) have been created. This trials show construction materials conditions with certain parameters. In the non-destructive group, we found ultrasounds whose spreading in this materials gives us information about their condition and internal structure. Among the multiple ultrasonic tests, we can find the ultrasonic tomography which is based in the Computed Tomography Scans (CT) basis: an object is illuminated by a source and signals are received through receivers. Rotation is made around the object under study combining the signals using tomographic algorithms for the purpose of obtaining an internal object reconstruction without damaging it. However we can assume a straight beam path for certain wavelengths, ultrasound are dispersive waves that diffract and reflect, making them less suitable because they worsen the quality of reconstructions. In this thesis, the ultrasonic tomography applied to mortar specimens is studied. For that, a study of tomographic reconstruction algorithms is carried out and the main conventional algorithms are reviewed. The transforms (FBD and DFT) whose results are excellent in case we have a high level of beams and directions that make up the projections. The neuronal network algorithms (BPE and RBF) and the ones for algebraic methods (ART, CART, SART and SIRT) have good results in situations where a low number of beams and directions or high noise presence are found. A comparation between them is made using projections obtained with simulated signals and the best FBP algorithm results are extracted. The following real reconstructions are carried out with this method. The application on which this work focuses consists of the detection of the carbonation front in cementitious specimens. That is why different types of specimens with damage and without damage are designed to validate a tomographic system function. A hardware system capable of taking automated measures using a configuration of parallel beams or fan beams is designed and built. Moreover, it has been adapted to be able to inspect both with air-coupled transducers and to inspect the object while submerged (water coupled). It is concluded that immersion tomography offers a compromise solution between energy transfer and automation process. Two models of neuronal networks trained through simulated sinograms are also implemented to reconstruct real cases afterwards. All the algorithms and cases are evaluated both in reconstruction quality and in features. / Gallardo Llopis, C. (2023). Tomografía ultrasónica para la evaluación de daño por gradiente en materiales cementantes [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/194552