Pour voir les autres types de publications sur ce sujet consultez le lien suivant : Teleseism.
Thèses sur le sujet « Teleseism »
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 50 meilleures thèses pour votre recherche sur le sujet « Teleseism ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les thèses sur diverses disciplines et organisez correctement votre bibliographie.
1
Pucciarelli, Giuseppe. « Seismic tomography of Italy (with special regard to Southern Tyrrhenian) ». Doctoral thesis, Universita degli studi di Salerno, 2017. http://hdl.handle.net/10556/2569.
Texte intégralRésumé :
2015 - 2016The topic of my PhD thesis is a seismic tomography which has as object of investigation Italy, particularly Southern Italy and Southern Tyrrhenian. This tomography has been obtained by means of inversion of teleseismic data. Seismic tomography is a method of investigation which is considerably stabilized in the field of Geophysics. Its goal is the achievement of a tridimensional velocity model of a subsoil of a determined area. For reaching this aim, it is necessary to gather arrival times of seismic events registered by seismic stations that are distributed in an opportune way on the area subject to process of investigation and an one-dimensional velocity model (that is, velocity only in function of depth). Through this last one, there is the computation of theoretical travel times for each pair seismic event – seismic station. This particular phase of method is called forward problem. Then, there is the computation of the difference between observed travel times and these theoretical travel times, a difference named residual. This is the description of so-called inverse problem. The computation happens in an iterative way and it stops when the residual is minimum. Obtained tridimensional velocity model corresponds with the model where residual is minimum. The entire process of operation of a seismic tomography is completely described in first chapter of this thesis. The second chapter describes the phenomen of subduction, that is of a particular process which happens, under determined conditions, at convergent boundaries of plates. I have dedicated a chapter to this phenomen because the area subject to this research, the basin of Southern Tyrrhenian, is a result of a roll-back subducting Ionian slab. After a paragraph dedicated to a general description of tectonic plates theory, other paragraphs describe the kinematics and the dynamics of subduction processes. This seismic tomography has been obtained by inversion of teleseismic travel times. This particular kind of choice has been made because teleseismic ray travel in upper mantle at high depths, so their inversion could supply us a good resolution of an area that we want to investigate until depth of 500-600 km. The third chapter of my PhD thesis is dedicated to teleseisms. In particular, there is a description of classification of seismic events according to their epicentral distance and how we can interpretate various seismic phases on a teleseismic seismogram. A paragraph is about the nomenclature of same seismic phases deriving from the reflection and the refraction of the waves on the discontinuity surfaces present in Earth's inner. The fourth and last chapter of my PhD thesis contains the results of research and their interpretation. First paragraph is dedicated to a brief summary of geological history of Southern Tyrrhenian. Second paragraph is dedicated to a description of software used for the research, that is FMTT (Fast Marching Teleseismic Transform), created by Nick Rawlinson in 2008. Third paragraph is dedicated to description of my data. I have utilised 1929 teleseisms (only P phases) recorded in period 1990-2012 by 122 southern Italian seismic station directly connected to ISC (International Seismological Centre). I have obtained several sections at various level of depth, from 25 km to 500 km and I have obtained several profiles NS and EW at fixed values of longitude from 14° to 16° and latitude, from 37° to 40° respectively. Results, compared with previous works in that area, confirm the presence of a subducting slab in Southern Tyrrhenian. Finally, my PhD thesis is enriched by various appendixes, which describe in a particular way mathematical techniques and geophysical definitions which I have used. [edited by author]
La mia tesi di Dottorato descrive una tomografia sismica dell'Italia, e in particolare di quella meridionale e del Basso Tirreno, ottenuta mediante l'inversione di dati telesismici. La tomografia sismica è oramai un metodo di indagine notevolmente consolidato nel campo della Geofisica e consiste nel ricavare un modello di velocità tridimensionale del sottosuolo di una determinata regione. Quest'ultimo si ottiene avendo a disposizione i tempi di arrivo di eventi sismici registrati da stazioni sismiche distribuite in maniera opportuna sull'area da indagare e un modello di velocità di partenza unidimensionale. Infatti, sfruttando quest'ultimo si calcolano per gli eventi sismici considerati dei tempi di arrivo teorici (questa fase prende il nome di PROBLEMA DIRETTO). Poi si calcola la differenza tra i tempi di arrivo realmente osservati e quelli teorici, che prende il nome di residuo (questa fase prende il nome di PROBLEMA INVERSO) e si procede in maniera iterativa in maniera che il residuo sia minimo. Il modello di velocità da ottenere è quello che corrisponde al residuo minimo. Il primo capitolo della tesi descrive la trattazione matematica della tomografia sismica, dopo un paragrafo introduttivo dedicato all'uso in generale dei metodi inversi in geofisica. La tomografia sismica si dice locale se gli eventi considerati sono locali. Si dice telesismica – come quella oggetto della mia tesi – se gli eventi considerati sono, lapalissianalmente, telesismi. Il secondo capitolo parla quindi dei telesismi, della loro definizione riguardo alla classificazione degli eventi sismici in base alla distanza epicentrale e delle fasi sismiche che si possono leggere da un sismogramma di un telesisma. Questo capitolo comprende un paragrafo sulla nomenclatura delle fasi sismiche e soprattutto quelle derivanti dalla riflessione e rifrazione delle onde su tutte le superfici di discontinuità presenti all'interno della Terra. E, a tal proposito, il terzo capitolo è un'introduzione alla struttura dell'interno della Terra con attenzione particolare che viene rivolta al fenomeno della subduzione. Questo perché uno slab di subduzione è presente all'interno del Basso Tirreno, zona “protagonista” della mia indagine tomografica. Il quarto capitolo è dedicato alla storia geologica del Basso Tirreno e alle evidenze delle precedenti indagini geofisiche che hanno visto questa area sotto la lente di ingrandimento. L'ultimo capitolo riguarda i risultati della mia indagine e la loro interpretazione. Ho utilizzato i tempi di arrivo di fasi P di 1929 telesismi (selezionati in base a un intervallo di magnitudo, a un minimo di stazioni registranti e all'intervallo di residuo di stazione) registrati nel periodo 1990-2012 da 122 stazioni dell'Italia centro-meridionale collegate all'ISC (International Seismological Centre). I risultati sembrerebbero, confrontati con quelli dei lavori precedenti, confermare la presenza di uno slab di subduzione nel Basso Tirreno. [a cura dell'autore]
XV n.s. (XXIX )
2
Burdick, Scott A. (Scott Anthony). « Teleseismic transmission and reflection tomography ». Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87516.
Texte intégralRésumé :
Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
The aim of seismic tomography is to determine a model of Earth properties that best explain observed seismic data. In practice, the limitations placed on our observations and computational capabilities force us to make a number of decisions about the scales and parameterizations of models, the nature of the data considered, and the approximations to wave propagation that connect the two. This thesis will consider three divergent approaches to seismic tomography spanning different representations of Earth structure at different scales, using different parts of the teleseismic wavefield, and solving the inverse problem with different approximations to the wave equation and different optimization methods. In choosing each of these approaches, we address two major decisions that influence the tomographic process: First, what relative value do we place on an less approximate treatment of wave physics versus the ability to incorporate as much information as possible in our inversion? Second, how can we use novel data to better constrain smooth seismic structure in regions that were previously unresolved? The first project presents a global ray-theoretical P-wave model that encompasses millions of traveltime picks. In this inversion, the addition of data from the dense USArray Transportable Array to global catalog data allows us to image the structure of the Eastern United States with unprecedented resolution and make a robust evaluation of the spatial scales of the heterogeneity. The second project develops a finite frequency approach to turning wave transmission tomography using a computationally efficient one-way wave propagation on curvilinear coordinates. The use of overturning coordinate systems allows for the application of wave equation tomography to phases previously unused in other oneway schemes. The final project presents a novel approach to wave-equation teleseismic reflection tomography using free surface multiples. The use of these multiply reflected phases helps to localize heterogeneity in the model to within layers of Earth structure. This project spans the final two chapters and includes the theoretical developments and an inaugural application to SsPmp data from the Hi-CLIMB array in Tibet.
by Scott A. Burdick.
Ph. D. in Geophysics
3
Henry, Chris. « Teleseismic studies of large submarine earthquakes ». Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249590.
Texte intégral
4
Foley, John Edward. « Crustal structure from teleseismic bodywave data ». Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/52914.
Texte intégralRésumé :
Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.Includes bibliographical references (leaves 245-255).
by John Edward Foley.
Sc.D.
5
Snowden, Conor B. « The complexity of teleseismic P-waves ». Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/11422.
Texte intégralRésumé :
Complex short-period teleseismic P-waveforms (consisting of the direct P wave and surface reflections pP and sP) are observed from many earthquake sources. It is often not possible to easily interpret these waveforms in terms of those three phases. This is necessary to obtain accurate earthquake depths and P and S wave radiation patterns. This thesis examines the contribution made by various factors to P-wave seismogram complexity using both synthetic and real data. First, using a number of synthetic waveforms it is confirmed that long duration sources can contribute significantly to the complexity of short-period waveforms. However, it is highlighted that by using broadband recordings much of this complexity can be accounted for, and attributed to the limited passband of the short-period recording system. In addition, S-to-P mode conversions at near-source structure can also contribute significantly to the complexity of the short-period waveform. Second, the causes of differences in the complexity of the short-period waveforms from the 1987 Whittier Narrows and the 1991 Sierra Madre earthquakes are examined. Originally these earthquakes were thought to be separated by a distance approximately the size of the first Fresnel Zone, and hence should, in theory, have indistinguishable near-source structure, when seen at teleseismic distances. Using relative amplitudes, the published CMT focal mechanism for these events is confirmed . In the case of Sierra Madre earthquake it was also possible to positively identify the one surface reflection, visible on the shortperiod seismogram, as pP. Even with complex waveforms the relative amplitude method can be used to place constraints on the focal mechanism of the Whittier Narrows earthquake. Using forward modelling, with a simple kinematic source model, synthetic seismograms are matched to the observed broadband seismograms for both earthquakes. Using this simple source model, the variation in the source duration, caused by the difference in source rupture areas between the two earthquakes, is sufficient to account for the first-order variations in complexity seen. To second order, the near-source structure is sufficiently different even at the limit of resolution of the data, to contribute to some extent to the observed complexity variation, most likely due to the large thickness of sediment west of the Sierra Madre Fault. Third, a suite of seismograms from the 29 October 1995 Caspian Sea earthquake is examined. Using relative amplitudes, the surface reflection on these seismograms is correctly identified and the actual depth estimated to be 48 km. From this it is shown that an arrival mis-identified by the Prototype International Data Center as a surface reflection is most likely to be be a mode conversion at an interface 80 km beneath the source. Forward modelling of the broadband and short-period waveforms shows that these mode-conversions are enhanced by the downward propagating line rupture, and are best seen when the position of the stations are at a node in the P-wave radiation pattern. This produces an apparently complex waveform. Visible S waves from this earthquake at European stations show the very low attenuation in the mantle path and this may contribute to the greater than usual complexity observed for this event. Finally several earthquakes that appear to show seismogram complexity that cannot be explained using a simple kinematic source model or path effects are examined. By modifying an existing finite-difference fault modelling code I present a possible dynamic source model that may provide one explanation for this additional complexity. This model includes real source physics (friction law, rupture criteria) and material heterogeneities. It produces complex farfield pulse shapes that vary with fault length, material heterogeneity, initial state of stress and attenuation.
6
Sargeant, Susanne. « Modelling shallow earthquakes with teleseismic broadband data ». Thesis, University of East Anglia, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251561.
Texte intégral
7
Ihmle, Pierre Frédéric. « Teleseismic study of rupture processes with long duration ». Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/54395.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994.Includes bibliographical references (p. 229-238).
by Pierre Frédéric Ihmle.
Ph.D.
8
Eken, Tuna. « Isotropic and Anisotropic P and S Velocities of the Baltic Shield Mantle : Results from Analyses of Teleseismic Body Waves ». Doctoral thesis, Uppsala universitet, Geofysik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-102501.
Texte intégralRésumé :
The upper mantle structure of Swedish part of Baltic Shield with its isotropic and anisotropic seismic velocity characteristics is investigated using telesesismic body waves (i.e. P waves and shear waves) recorded by the Swedish National Seismological Network (SNSN). Nonlinear high-resolution P and SV and SH wave isotropic tomographic inversions reveal velocity perturbations of ± 3 % down to at least 470 km below the network. Separate SV and SV models indicate several consistent major features, many of which are also consistent with P-wave results. A direct cell by cell comparison of SH and SV models reveals velocity differences of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially caused by noise and limited resolution, and some features are attributed to the effect of large scale anisotropy. Shear-wave splitting and P-travel time residual analyses also detect anisotropic mantle structure. Distinct back-azimuth dependence of SKS splitting excludes single-layer anisotropy models with horizontal symmetry axes for the whole region. Joint inversion using both the P and S data reveals 3D self-consistent anisotropic models with well-defined mantle lithospheric domains. These domains of differently oriented anisotropy most probably retain fossil fabric since the domains' origin, supporting the idea of the existence of an early form of plate tectonics during formation of continental cratons already in the Archean. The possible disturbing effects of anisotropy on seismic tomography studies are investigated, and found to be potentially significant. P-wave arrival times were adjusted based on the estimates of mantle anisotropy, and re-inverted. The general pattern of the velocity-perturbation images was similar but changed significantly in some places, including the disappearance of a slab-like structure identified in the inversion with the original data. Thus the analysis demonstrates that anisotropy of quite plausible magnitude can have a significant effect on the tomographic images, and should not be ignored. If, as we believe, our estimates of anisotropy are reasonably correct, then the model based on the adjusted data should give a more robust and correct image of the mantle structure.
9
Letort, Jean. « Méthodes télésismiques d'estimation de la profondeur des séismes : développements et applications ». Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU016/document.
Texte intégralRésumé :
Cette thèse traite de l'étude de la profondeur des séismes modérés (4 < M < 5.5), à travers l'utilisation de données telesismiques, c'est à dire à partir d'enregistrements de sismographes situes a des distances de 3000 jusqu'à 9000 km de la source. L'estimation de la profondeur d'un séisme s'obtient en comparant les temps d'arrivée de l'onde directe (P) générée par ce séisme, avec ceux des ondes réfléchies sur la surface de la Terre, au-dessus du foyer du séisme (les phases de profondeur pP, sP). Nous utilisons le réseau du CTBTO (Comprehensive Test-Ban-Treaty-Organization, composé de mini-réseaux (10-20 sismographes), nous permettant de développer deux nouvelles méthodes d'estimation de la profondeur. La première est une inversion complète du mécanisme au foyer, simultanément a la profondeur. La seconde est une méthode d'analyse spectrale : le cepstre. A l'aide d'exemples de séismes en zone intracontinentale, nous montrons que ces deux méthodes sont complémentaires et qu'elles apportent une information nouvelle sur l'estimation de la profondeur pour les séismes de régions peu instrumentées. Dans un second temps, une optimisation de la méthode cepstrale a permis d'étendre l'estimation de la profondeur a l'utilisation de stations isolées provenant du réseau mondial IRIS. Cette nouvelle méthode, complètement automatique, a permis de localiser en profondeur les séismes de magnitude supérieure à 4.5 pour la zone de subduction de Guerrero (Mexique). Nous avons ainsi mis en évidence une répartition homogène des profondeurs des séismes dans la zone du gap de Guerrero. En combinant ces estimations de la profondeur de l'interface avec celles obtenues a l'aide d'une relocalisation de l'ensemble de la sismicité (par la méthode de l'ISC-Locator), nous proposons une imagerie de la géométrie de la subduction. Nous avons ensuite étudié l'influence de la profondeur sur les propriétés sismiques des séismes. En particulier, nous avons évalué la relation entre la profondeur et la chute de contrainte pour les séismes récents et modérés de la plaine du Pô, en Italie. Pour cela, nous nous sommes appuyés sur le réseau accéléromètrique régional de l'INGV Milan pour estimer les spectres sources de ces séismes, puis en déduire les fréquences coins et les chutes de contraintes associées. Ces spectres sources s'obtiennent à l'aide d'une méthode d'inversion qui sépare simultanément l'effet de l'atténuation, les effets de sites et l'effet de la source sur les spectres des ondes S, générées par les séismes et enregistrées en surface par les accéléromètres. Après inversion, nous trouvons une faible augmentation de la chute de contrainte avec la profondeurThis thesis deals with depth estimations of moderate earthquakes (4 < M < 5.5), observed through the use of teleseismic data. At teleseismic distances (from 3000 to 9000 km), estimations of earthquake depths come from the estimation of the delays between the arrival time of the direct P-wave and the arrival times of the waves which have been reflected on the surface above the source (known as : depth phases pP and sP). The CTBTO (Comprehensive Test-Ban- Treaty-Organization) monitoring system allows the detection of these teleseismic phases for weak events, with magnitudes below 5, since this global network is composed by arrays (10-20 close single stations, in the same location). Using this network, two methods were developed for teleseismic depth estimation. First, a depth-phase recognition method is applied, based on a new improved cepstral analysis. In addition, we have developed a focal mechanism genetic algorithm inversion. We have applied these two methods for earthquakes occurring in intracontinental areas and we have proved that these new depth determinations provide new and complementary information about the source for barely instrumented areas. We have also developed another method, completely blind and automatic, which consists in an improvement of the cepstral analysis. The reliability of this method to improve depth estimation has been proved by relocating the recent moderate seismicity of the Guerrero subduction area (Mexico). In the Guerrero area, this cepstral analysis efficiently clusters event locations. We then use teleseismic waves reflected on the subduction interface to evaluate the depth of the interface above the focal hypocenter, which allows to specify the subduction interface geometry. We have finally conducted an exhaustive analysis of the depth distributions, based on a relocalization of the ISC catalogue using the new ISC-Locator algorithm and we provide an improved image of the subduction. Finally, we have conducted a study of the relationship between earthquake depths and seismic properties. In particular, we have focused on the burning issue about the links between stress drops and focal depths. We have found an interesting case study with the Po Plain recent seismicity (Northern Italy). Brune's stress drops and magnitudes have been estimated from a generalized parametric inversion using the regional accelerometric network from INGV Milano. We have shown that there is only a slight dependency between stress drops and earthquake depths in the Po Plain
10
Jiang, Wei Ping. « Determination of crustal velocity structures from teleseismic p waves ». Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/25773.
Texte intégral
11
Morice, Stephen Patrick. « A receiver function study in the Peloponnese, Greece ». Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264508.
Texte intégral
12
Lipke, Katrin, Max Zitzmann, Manuel Amberger, Carsten Ehlert, Dirk Rößler, Frank Krüger et Matthias Ohrnberger. « Traveltime residuals at regional and teleseismic distances for SE-Asia ». Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2007/1411/.
Texte intégralRésumé :
Traveltime residuals for worldwide seismic stations are calculated. We use P and S waves from earthquakes in SE-Asia at teleseismic and regional distances. The obtained station residuals help to enhance earthquake localisation.
Furthermore we calculated regional source dependent station residuals. They show a systematic dependence of the locality of the source. These source dependent residuals reflect heterogenities along the path and can be used for a refinement of earthquake localisation.Laufzeitresiduen für weltweite seismische Stationen werden berechnet. Wir nutzen P - und S-Wellen von Erdbeben in Südostasien in teleseismischen und regionalen Distanzen. Die so erhaltenen Stationsresiduen helfen, die Lokaliesierung von Erdbeben zu verbessern. Außerdem berechnen wir regional quellabhängige Stationsresiduen. Diese zeigen eine systematische Abhänbgigkeit vom Ort der Quelle. Sie spiegeln Heterogenitäten entlang des Strahlweges wieder und können für eine Verfeinerung der Ersbebenlokaliesierung genutzt werden.
13
Baker, Benjamin Ian. « 2.5d teleseismic waveform tomography with application to the tien shan ». Thesis, Rensselaer Polytechnic Institute, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3613267.
Texte intégralRésumé :
The analysis of passive source seismic data recorded by quasi-linear deployments of broadband stations at teleseismic distances has proven to be an effective means of probing the subsurface of the Earth. However, current methodologies are far from being able to exploit all the interpretable signal in these data sets. In this thesis, I describe a 2.5D, frequency domain, visco-elastic waveform tomography algorithm for imaging with this type of data. To compute synthetic seismograms (the forward problem), the general equations of motion are discretized with p-adaptive finite elements. This approach allows for geometric flexibility and accurate solutions as a function of wavelength. Artificial force distributions manifesting Huygen's principle for the teleseismic events are introduced locally through a Bielak layer. Because of the relatively low frequency content of teleseismic data, regional scale tectonic settings can be parameterized with a modest number of variables and perturbations can be determined directly from a regularized Gauss-Newton system of equations. Waveforms generated by the forward problem compare well with analytic solutions for simple 1D media and with those generated in heterogeneous structures by a finite difference technique. It is demonstrated through examples that the regularized approximate Hessian is particularly effective at focusing backpropagated residuals to their true location. It is observed that full waveform inversion can provide significantly better vertical resolution than arrival time tomography and significantly better lateral resolution than standard surface wave tomography. Used in tandem in a multi-scale approach, surface wave tomography followed by joint surface wave/body wave tomography is shown to be an effective strategy for image reconstruction from a simple starting model. This inversion strategy is then applied to body and surface wave teleseismic waves recorded in the Tien Shan. The work of previous investigators is both corroborated and better illuminated by starting from a 1D model and inverting with this joint multi-scale approach. The main results for this application are (1) that the Tarim basin appears to be underthrusting the Tien Shan from the south, (2) a thin crust overlaying a piece of suspected relict lithosphere exists below the Naryn valley, and (3) there is a south dipping high velocity zone on the north side of the Tien Shan suggesting consumption of the Chu depression and the Kazak shield. The north dipping high velocity feature in the south and south dipping high velocity feature in the north are consistent with the hypothesis of dual subduction beneath the Tien Shan.
14
Yu, Chunquan Ph D. Massachusetts Institute of Technology. « Imaging of crust and mantle structures with teleseismic reflected waves ». Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104597.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references.
In this thesis, we developed and applied seismic imaging methods based on teleseismic reflected waves to study discontinuities in the crust and mantle. Specifically, we further developed virtual deep seismic sounding (VDSS) to probe the Moho and we used SS precursors to study mantle transition zone discontinuities. To extend the applicability of VDSS, we developed a source deconvolution scheme to remove complex source signatures of shallow earthquakes. Application of VDSS to data from the North China craton reveals significant lateral variations in crustal thickness. Assuming that the crust was originally uniform, the thick crust beneath the Ordos plateau supports the hypothesis of lower crustal foundering as the mechanism of reactivation of the eastern North China craton. Application of VDSS to the entire western United States suggests significant, but highly variable, mantle contribution to surface topography. Although thermal anomalies are the main contribution to high elevation of the western US cordillera, our results suggest that petrological heterogeneities or dynamic forces must also play a role in mantle buoyancy. To improve mantle transition zone imaging, we developed an array processing technique to remove random and signal-generated noise that contaminating SS precursors. Application of our scheme to data that sample the Central Pacific greatly improves both the travel time picks and amplitude measurements of SS precursors. The observed changes in reflectivity over distance yield density contrast across 410-km and 660-km discontinuities that are well below those in the PREM model. The density and Vs contrasts across the 410-km discontinuity are consistent with upper mantle composition containing 45% olivine, which is intermediate between piclogite and pyrolite models of mantle composition. Lateral variations in density and Vs contrasts across the 660-km discontinuity are observed, perhaps indicating compositional heterogeneities at the base of the mantle transition zone.
by Chunquan Yu.
Ph. D.
15
Scire, Alissa. « Imaging Variations in the Central Andean Mantle and the Subducting Nazca Slab with Teleseismic Tomography ». Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/556487.
Texte intégralRésumé :
The Nazca-South America convergent margin is marked by the presence of the Andean mountain belt, which stretches along the 8000-km long western margin of the South American plate. The subduction zone is characterized by significant along-strike changes in both upper plate structure and slab geometry that make it an ideal region to study the relationship between the subducting slab, the surrounding mantle, and the overriding plate. This dissertation summarizes the results of three finite frequency teleseismic tomography studies of the central Nazca-South America subduction zone which improve our understanding of how along-strike variations in the Andean mountain belt and the subducting Nazca plate interact with each other and with the surrounding mantle. This is accomplished by first focusing on two smaller adjacent regions of the central Andes to explore upper mantle variations and then by using a combined dataset, which covers a larger region, to image the deeply subducted Nazca slab to investigate the fate of the slab. The first study focuses on the central Andean upper mantle under the Altiplano-Puna Plateau where normally dipping subduction of the Nazca plate is occurring (18° to 28°S). The shallow mantle under the Eastern Cordillera is generally fast, consistent with either underthrusting of the Brazilian cratonic lithosphere from the east or a localized "curtain" of delaminating material. Additional evidence for delamination is seen in the form of high amplitude low velocities under the Puna Plateau, consistent with proposed asthenospheric influx following lithospheric removal. In the second study, we explore the transition between normal and flat subduction along the north edge of the Altiplano Plateau (8° to 21°S). We find that the Peruvian flat slab extends further inland along the projection of the Nazca Ridge than was previously proposed and that when re-steepening of the slab occurs, the slab dips very steeply (~70°) down through the mantle transition zone (MTZ). We also tentatively propose a ridge parallel tear along the north edge of the Nazca Ridge. Both of these observations imply that the presence of the Nazca Ridge is at least locally influencing the geometry of the flat slab. The final study investigates along-strike variations in the deeply subducted Nazca slab along much of the central Nazca-South America subduction zone (6° to 32°S). Our results confirm that the Nazca slab continues subducting into the lower mantle rather than remaining stagnant in the MTZ. Thickening of the slab in the MTZ north of 16°S is interpreted as folding or buckling of the slab in response to the decreased slab sinking velocities in the lower mantle.
16
Fan, Chengliang. « Extracting P-primary transmission and reflection impulse responses from teleseismic data ». [Bloomington, Ind.] : Indiana University, 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3199414.
Texte intégralRésumé :
Thesis (Ph.D.)--Indiana University, Dept. of Geological Sciences, 2005.Source: Dissertation Abstracts International, Volume: 66-11, Section: B, page: 5867. Adviser: Gary L. Pavlis. Title from dissertation home page (viewed Oct. 11, 2006).
17
Condori, Cristobal, George S. França, Hernando J. Tavera, Diogo F. Albuquerque, Brandon T. Bishop et Susan L. Beck. « Crustal structure of north Peru from analysis of teleseismic receiver functions ». PERGAMON-ELSEVIER SCIENCE LTD, 2017. http://hdl.handle.net/10150/625974.
Texte intégralRésumé :
In this study, we present results from teleseismic receiver functions, in order to investigate the crustal thickness and Vp/Vs ratio beneath northern Peru. A total number of 981 receiver functions were analyzed, from data recorded by 28 broadband seismic stations from the Peruvian permanent seismic network, the regional temporary SisNort network and one CTBTO station. The Moho depth and average crustal Vp/Vs ratio were determined at each station using the H-k stacking technique to identify the arrival times of primary P to S conversion and crustal reverberations (PpPms, PpSs + PsPms). The results show that the Moho depth correlates well with the surface topography and varies significantly from west to east, showing a shallow depth of around 25 km near the coast, a maximum depth of 55-60 km beneath the Andean Cordillera, and a depth of 35-40 km further to the east in the Amazonian Basin. The bulk crustal Vp/Vs ratio ranges between 1.60 and 1.88 with the mean of 1.75. Higher values between 1.75 and 1.88 are found beneath the Eastern and Western Cordilleras, consistent with a mafic composition in the lower crust. In contrast values vary from 1.60 to 1.75 in the extreme flanks of the Eastern and Western Cordillera indicating a felsic composition. We find a positive relationship between crustal thickness, Vp/ Vs ratio, the Bouguer anomaly, and topography. These results are consistent with previous studies in other parts of Peru (central and southern regions) and provide the first crustal thickness estimates for the high cordillera in northern Peru.
18
Ashoori, Pareshkoohi Azadeh. « Lithospheric Structure Across the Northern Canadian Cordillera from Teleseismic Receiver Functions ». Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35535.
Texte intégralRésumé :
A major change in seismic velocities between Earth’s crust and mantle is known as the Mohorovicic discontinuity (Moho). The depth of the Moho plays an important role in characterizing the overall structure of the crust and can be related to the tectonic setting of a region. Teleseismic P-wave receiver function techniques can provide estimates of the depth of the Moho and therefore crustal thickness under a broadband station. In this research we are interested in the structure of the crust and mantle across the northern Canadian cordillera, described by various tectonic settings. The teleseismic data recorded by broadband three-component seismic stations are used to perform receiver function analysis to determine the lateral variations of Moho depth under northern Canadian cordillera and map out the crustal thickness under the broadband stations. Based on visual inspection of receiver function results in the region, we find evidence of anisotropy or dipping reflectors in the crustal structure of the northern cordillera observed in back-azimuthal variations of transverse component receiver functions. We further provide a quantitative interpretation of receiver function in terms of anisotropy or dipping structure by decomposing the azimuthal variations of depth migrated receiver functions into back-azimuthal harmonics. This technique can be used to map out the orientation of anisotropy that may be related to cracks and/or rock texture caused by deformation. We resolve the Moho at an average depth of ~35 km along the western profile of the study area. Harmonic decomposition along the study area yields crustal anisotropy at depth 5-20 km, which does not extend in the lower crust. This can be the result of complex deformation at a detachment zone like a quasi-rigid displacement of the upper crust over a lower crust. The detected anisotropy over the study area is not coherent as the slow symmetry directions detected by harmonic decomposition are highly variable.
19
Rondenay, Stéphane. « Teleseismic imaging of the southeastern Canadian Shield and Cascadia subduction zone ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ61166.pdf.
Texte intégral
20
Mercier, Jean-Philippe. « Improved teleseismic Green's functions and western Canada mantle structure and evolution ». Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2779.
Texte intégralRésumé :
The present thesis is divided into three distinct parts and focuses both on the improvement of deconvolution technique in a teleseismic context for crustal and upper-mantle studies and on the understanding of western Canada structure and evolution through seismic imaging. The first part presents estimates of the P-component of the teleseismic-P Green's functions for three stations of the Canadian National Seismic Network (CNSN) obtained using a new deconvolution technique. Our results show evidence of the principal, first-order scattered Moho phases and, in particular, the Pp_Mp. The second part presents teleseismic receiver functions from 20 broadband three-component seismometers deployed along the MacKenzie-Liard Highway in Canada's Northwest Territories as part of the joint Lithoprobe-IRIS CAnadian NOrthwest Experiment (CANOE). These stations traverse a Paleoproterozoic suture and subduction zone that has been previously documented in detail to mantle depths using seismic reflection profiling. Our results reveal the response of the ~1.8 Ga subduction zone on both the radial and transverse component. The identification of this structure and its comparison with fine-scale mantle layering below the adjacent Slave province and from a range of Precambrian terranes provides an unambiguous connection between fossil subduction and fine-scale, anisotropic mantle layering found beneath cratons. Previous documentation of similar layering below the adjacent Slave province provides strong support for the thesis that early cratonic blocks were stabilized through processes of shallow subduction. The last part presents P- and S wave velocity models for western Canada. In this part, we focus our attention on two distinct features: 1) the transition from Phanerozoic to cratonic mantle in northwestern Canada and 2) the complex tectonic environment at the northern terminus of the Cascadia subduction zone where the plate boundary changes from convergent to transform. We find that the main transition from Phanerozoic to cratonic mantle in northwestern Canada occurs at the Cordilleran deformation front. In northern Cascadia, we have imaged and characterized the signature of the subducting Juan de Fuca plate and observed evidence of subduction beyond the northern edge of the slab. Our result show that the Anahim hotspot track is underlain by a -2% low-velocity zone.
21
Marson-Pidgeon, Katrina Ann, et katrina marson-pidgeon@anu edu au. « Seismogram synthesis for teleseismic events with application to source and structural studies ». The Australian National University. Research School of Earth Sciences, 2001. http://thesis.anu.edu.au./public/adt-ANU20010925.152548.
Texte intégralRésumé :
The aim of this thesis is to develop procedures for the modelling and inversion of teleseismic P and S waveforms which are as flexible as possible. This flexibility is necessary in order to obtain accurate source depth and mechanism estimates for small to moderate size events, such as those that are relevant in the context of monitoring the Comprehensive Nuclear-Test-Ban Treaty (CTBT). ¶
The main challenge for extending source depth and mechanism inversion methods to smaller events is to ensure that sufficiently accurate synthetic seismograms are available for comparison with observed records. An accurate phase-adaptive reflectivity method has therefore been developed, against which the performance of less computationally intensive approximations can be judged. The standard reflectivity method has been modified to allow for different crustal and upper mantle structures at the source and receiver, and the full effects of reverberations and conversions in these structures can be allowed for. Core reflections and refractions can also be included; these phases can become important at certain distance ranges. A slowness bundle approach has been developed, where a restricted slowness integration about the geometric slowness for the direct wave is undertaken at each frequency, allowing accurate results to be obtained whilst avoiding the expense of a full reflectivity technique. ¶ Inversion using the neighbourhood algorithm (NA) is performed for source depth, mechanism and time function, by modelling direct P and S and their surface reflections (pP, sP and pS, sS) at teleseismic distances. Both SV and SH data are exploited in the inversion, in addition to P data, in order to obtain improved constraints on the source mechanism, including any isotropic component. Good results are obtained using a simple generalised ray scheme, however, the use of a flexible derivative-free inversion method means that more accurate synthetics are able to be used in the inversion where appropriate. The NA makes use of only the rank of the data misfits, so that it is possible to employ any suitable misfit criterion. In the few cases where control on the source mechanism is limited, good depth resolution is still usually obtained. ¶The structures near the source and receiver play an important role in shaping the detail of the teleseismic waveforms. Although reasonable results can be achieved with simple synthetics and a standard velocity model, significant improvement can be made by modifying the representation of structure near the source and receiver. In the case of sub-oceanic events it is important to allow for the effects of water reverberations. The crustal structure near the receiver can also have quite a large influence on the waveforms through reverberations and conversions. This is exploited in receiver function inversion, which is again accomplished using the NA approach.
22
Adams, David C. 1952. « Effects of noise on teleseismic T* estimation and attenuation tomography of the Yellowstone region ». Thesis, University of Oregon, 2009. http://hdl.handle.net/1794/10368.
Texte intégralRésumé :
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
23
Shomali, Z. Hossein. « Dynamic Source Models of Icelandic Earthquakes and Teleseismic Tomograhy along the TOR array ». Doctoral thesis, Uppsala University, Department of Earth Sciences, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1451.
Texte intégralRésumé :
This thesis describes new inversion-oriented methodological developments and their seismological applications. In the first study presented the dynamic source parameters of some local Icelandic earthquakes are studied by employing a time domain moment tensor inversion method. A windowing method for direct P and S phases was used and the inversion was performed for frequencies lower than the associated corner frequency under the double-couple constraint. The inversion algorithm could determine the dynamic source parameters correctly, even under conditions of poor azimuthal coverage. The second study deals with a new method for calculating the empirical Green's function based on inversion of earthquake radiation patterns. The resulting Green's functions then may contain both body and surface waves. The validity of the method was then confirmed by applying the method to some Icelandic earthquakes. The lithosphere-asthenosphere transition along the TOR array is investigated in the last two studies. Separate and simultaneous teleseismic P and S relative arrival-time residuals were inverted via different methods (a singular value decomposition and a quadratic programming method) to investigate the reliability and the resolution of the model. The data were corrected a priori for the effect of travel-time perturbations due to crustal structure. The results indicate that the transition between thinner lithosphere in Germany to the thicker Baltic Shield in Sweden occurs in two sharp and steep steps. A sharp and steep subcrustal boundary is found below the Tornquist Zone, with a less significant transition below the Elbe Lineament. The lithospheric structure appears to be about 120 km thick under the Tornquist Zone, increasing to more than 200 km beneath the Baltic Shield.
24
Shomali, Z. Hossein. « Dynamic source models of Icelandic earthquakes and teleseismic tomography along the TOR array / ». Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5098-9/.
Texte intégral
25
Tomlinson, James Peter. « A teleseismic receiver function study of the crustal structure of the British Isles ». Thesis, University of Leicester, 2003. http://hdl.handle.net/2381/30454.
Texte intégralRésumé :
The onshore crustal and upper mantle velocity structure of the British Isles has been investigated by teleseismic receiver function analysis. The results of the study augment the dense offshore and sparse onshore models of the structure beneath the area. In total almost 1500 receiver functions have been analysed, which have been calculated using teleseismic data from 34 broadband and short-period, three-component seismic recording instruments. The crustal structure has primarily been investigated using 1D grid search and forward modelling techniques, returning crustal thicknesses, bulk crystal Vp/Vs ratio and velocity-depth models. Upper mantle structures have been investigated by applying Ps moveout corrections and migration techniques to the observed broadband receiver functions. H-k stacking reveals crustal thicknesses between 25-36 km and Vp /Vs ratios between 1.6-1.9. The crustal thicknesses correlate with the results of previous seismic reflection and refraction profile to within +/- 2km. The exceptions are the stations close to the lapetus suture where the receiver function crustal thicknesses are up to 5 km less than the seismic refraction Moho. This mismatch has been attributed to the presence of underplated magmatic material at the base of the crust. 1D forward modelling has revealed sub-crustal structures. In northern Scotland these correspond with the Flannan and W-reflectors. The isolated sub-crustal structure at station GIM on the Isle if Man may be related to the closure of the lapetus ocean. Ps conversion from the 410 km and 660 km discontinuities have been identified in the Ps moveout corrected receiver functions. The differential delay time between the phases is close to the global average of 24s, indicating that there is no significant thermal anomaly in the mantle transition zone beneath the British Isles. A discontinuity at ~220 km has been identified as the Lehmann discontinuity. A 30 km step in the Lehmann discontinuity close to the lapetus suture may be interpreted as juxtaposition of Laurentian and Avalonian mantle.
26
Corradini, Marina. « Reconstruction of the earthquake rupture process through coherent teleseismic imaging and statistical modeling ». Thesis, Université de Paris (2019-....), 2019. https://theses.md.univ-paris-diderot.fr/CORRADINI_Marina_va1.pdf.
Texte intégralRésumé :
De nombreuses études ont tenté d’éclairer la complexité de la rupture sismique de grands séismes en utilisant des techniques d’imagerie cohérente telles que la back- projection (BP). Dans une étude récente, Fukahata et al. (2013) ont suggéré que, d’un point de vue théorique, l’image BP de la rupture sismique est liée au glissement ou à la vitesse de glissement sur la faille. Cependant, la relation quantitative entre les images BP et les propriétés physiques du processus de rupture reste encore peu connue. Cette thèse vise à clarifier comment les images BP du champ d’ondes rayonné peuvent être utilisées pour déduire les hétérogénéités spatiales en glissement et en vitesse de rupture le long de la faille. Nous réalisons des simulations de différents processus de rupture à l’aide d’un modèle de source linéaire. Pour chaque modèle de rupture, nous calculons les sismogrammes synthétiques à trois réseaux télésismiques et nous appliquons la technique de BP afin d’identifier les sources de rayonnement haute fréquence (HF). Cette procédure permet de comparer les images BP avec le modèle de rupture originaire et d’interpréter les émissions HF en fonction des trois paramètres cinématiques: le temps de montée, la valeur du glissement final, la vitesse de rupture. Nos résultats montrent que les pics HF extraits avec l’analyse BP sont le plus étroitement associés aux hétérogénéités spatio-temporelles de l’accélération du glissement. Nous vérifions nos observations sur deux grands séismes survenus dans la faille de Swan Islands à neuf ans d’intervalle: le séisme du 2009 (Mw 7.3) et celui du 2018 (Mw 7.5) au nord du Honduras. Les deux événements montrent une géométrie linéaire, ce qui les rend comparables à notre approche synthétique. Malgré la géométrie simple, les deux séismes sont caractérisés par un taux de glissement complexe, avec plusieurs sous-événements. Nos résultats préliminaires montrent que l’image BP des émissions HF permet d’estimer une longueur et une vitesse de rupture compatibles avec d’autres études et qu’un fort rayonnement HF pourrait correspondre aux zones de forte variabilité du taux de glissement. En conclusion, nous utilisons une méthode de réseau de neurones afin de prédire les paramètres cinématiques d’une rupture sismique à partir de son image BP. Le réseau s’appuie sur un grand nombre de processus de rupture synthétiques et leurs images BP, dans le but d’identifier le lien statistique entre le rayonnement HF et les paramètres cinématiques. Nos résultats montrent que le réseau de neurones appliqué à l’image BP du séisme est capable de prédire les valeurs du temps de montée et de la vitesse de rupture le long de la faille, ainsi que la position moyenne de l’hétérogénéité. Par contre, le réseau de neurones n’arrive pas à récupérer les valeurs du glissement final, auquel l’approche BP est relativement insensible. Notre étude permet de mieux comprendre l’écart qui existe actuellement entre la description théorique de la génération de rayonnements HF et les observations d’émissions HF obtenues par des techniques d’imagerie cohérentes, en s’appuyant aux pistes d’action possibles et en suggérant de nouvelles perspectivesMany studies have attempted to illuminate rupture complexities of large earthquakes through the use of coherent imaging techniques such as back-projection (BP). Recently, Fukahata et al. (2013) suggested that, from a theoretical point of view, the BP image of the rupture is related to the slip motion on the fault. However, the quantitative relationship between the BP images and the physical properties of the earthquake rupture process still remains unclear.Our work aims at clarifying how BP images of the radiated wavefield can be used to infer spatial heterogeneities in slip and rupture velocity along the fault. We simulate different rupture processes using a line source model. For each rupture model, we calculate synthetic seismograms at three teleseismic arrays and we apply the BP technique to identify the sources of high-frequency (HF) radiation. This procedure allows for the comparison of the BP images with the originating rupture model, and thus the interpretation of HF emissions in terms of along-fault variation of the three kinematic parameters: rise time, final slip, rupture velocity. Our results show that the HF peaks retrieved from BP analysis are most closely associated with space-time heterogeneities of slip acceleration. We verify our findings on two major earthquakes that occurred 9 years apart on the strike-slip Swan Islands fault: the Mw 7.3 2009 and the Mw 7.5 2018 North of Hondurasearthquakes. Both events followed a simple linear geometry, making them suitable for comparison with our synthetic approach. Despite the simple geometry, both slip-rate functions are complex, with several subevents. Our preliminary results show that the BP image of HF emissions allows to estimate a rupture length and velocity which are compatible with other studies and that strong HF radiation corresponds to the areas of large variability of the moment-rate function. An outstanding question is whether one can use the BP image of the earthquake to retrieve the kinematic parameters along the fault. We build on the findings obtained in the synthetic examples by training a neural network model to directly predict the kinematic parameters along the fault, given an input BP image. We train the network on a large number of different synthetic rupture processes and their BP images, with the goal of identifying the statistical link between HF radiation and rupture kinematic parameters. Our results show that the neural network applied to the BP image of the earthquake is able to predict the values of rise time and rupture velocity along the fault, as well as thecentral position of the heterogeneity, but not the absolute slip values, to which the HF BP approach is relatively insensitive. Our work sheds some light on the gap currently existing between the theoretical description of the generation of HF radiation and the observations of HF emissions obtained by coherent imaging techniques, tackling possible courses of action and suggesting new perspectives
27
Arlitt, Robert. « Teleseismic body wave tomography across the Trans-European suture zone between Sweden and Denmark / ». [S.l.] : [s.n.], 1999. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13501.
Texte intégral
28
Cassidy, John Francis. « Teleseismic receiver function analysis of the crust and upper mantle of southwestern British Columbia ». Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/30966.
Texte intégralRésumé :
The northern Cascadia subduction zone has been the site of numerous geophysical studies during the past two decades. However, little is known of the deep structure (> 40 km) or S-velocities throughout this region. In this study, locally generated P-to-S conversions (Ps) contained in ~100 teleseismic P-wave coda have been analysed to determine the S-velocity structure to upper mantle depths.
Prior to the analysis, the applications and limitations of this technique as applied to a dipping layer environment have been examined. It is concluded that strict stacking bounds (≤ 10° in ∆ and BAZ) should be applied. It is demonstrated that dipping boundaries which could not be detected using this technique (e.g. ∆Vs = 0.08 km/s), may significantly alter the amplitude and arrival time of reverberations from deeper interfaces. Therefore, such phases should not be quantitatively modelled. As reverberations are an important constituent of receiver functions, formal inversion of these waveforms is not justified in this environment. Only arrivals which exhibit the amplitude and arrival time characteristics of primary P-to-S conversions are considered in this study. Finally, most studies have normalised receiver functions to unit amplitude prior to modelling. However, synthetic data demonstrate that undetected dipping boundaries may alter Ps/P ratios and lead to inaccurate earth models. A recent modification to this technique (Ammon, 1991) which provides 'absolute' amplitudes is examined. In addition to providing information on the near-surface velocity structure and on dipping layers, this modification provides for a more accurate image of the earth structure.
Three 3-component broadband event triggered seismic stations were deployed in a 90 km long linear array oriented perpendicular to the continental margin of southwestern British
Columbia. Between December 1987 and October 1989 approximately 100 teleseisms covering
a wide azimuthal and distance range were recorded and analysed.
The two largest phases observed in data from the westernmost station ALB-B reveal a prominent low-velocity zone extending from 37-41 km depth beneath central Vancouver Island. This feature correlates well with the reflective 'E' zone, a region which also exhibits high electrical conductivity. Combining the S-velocity estimates with refraction P-velocities yields a high Poisson's ratio for this layer. The low P- and S-velocities and high Poisson's ratio and electrical conductivity are supportive of the recent interpretation of this feature as a fluid-saturated shear zone above the subducting Juan de Fuca (JdF) plate. Analysis of data at the mid-array and easternmost sites, LAS and EGM respectively, permits this zone to be mapped northeastward to a depth of 54 km beneath the British Columbia mainland, approximately 250 km from the locus of subduction.
The subducting oceanic crust is imaged at 47-53 km depth dipping 15°±5° in the direction N30°E±20° beneath central Vancouver Island. The dip angle increases to 22° ±5° at a depth of 60-65 km beneath the Strait of Georgia. The results of this analysis provide the first definitive evidence for the location of the subducting plate in this region and indicates that the seismicity at depth occurs within the oceanic crust. Further, the dip direction of N30°E supports the theory (Rogers, 1983) that the JdF plate is arched upwards as it subducts in this region.
Finally, the continental Moho is imaged at 36 km depth beneath LAS, and there is evidence
at both this site and EGM for a low-velocity zone in the lower crust. A similar feature is imaged beneath Vancouver Island and coincides with the reflective ‘C’ zone. The depth estimated to the top of this layer denotes the lower limit of shallow seismicity suggesting a significant structural or compositional change at a depth of 20-26 km.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
29
Chen, Chin-Wu Ph D. Massachusetts Institute of Technology. « Teleseismic imaging of the Slave craton and implications for the assembly of cratonic lithosphere ». Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/58394.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 123-132).
In this dissertation, I investigate the assembly and evolution of the Archean cratonic lithosphere by using two complementary seismological methods to image the lithospheric structure of the Slave craton in Canada. First, I perform surface wave tomographic inversions to constrain the depth dependence of Rayleigh wave phase velocity, shear wave velocity, and azimuthal anisotropy of the Slave cratonic lithosphere. The tomographic images reveal high shear wave velocities associated with a particularly depleted, cold, and unperturbed Archean cratonic lithosphere. Furthermore, the inversions reveal distinct anisotropic domains in the crust, the lithospheric mantle, and the sub-lithospheric mantle. These results reflect the evolutionary history of the cratonic lithosphere. Secondly, I image seismic discontinuities in the lithosphere using receiver-function analysis of converted P-to-S waves. The resulting seismic profile shows a pronounced low velocity discontinuity at -100 km depth beneath the central Slave craton. This seismic discontinuity shows striking spatial correlation with both an electrical conductive anomaly derived from magnetotelluric sounding, as well as a petrologically-defined ultra-depleted layer. The synthesis of coincident seismic, electrical, and petrological evidence supports that this geophysical and petrological boundary represents a compositional interface marked by alteration minerals. I suggest that this mineralization resulted from relict metasomatism associated with an Archean subduction event, which played an important role in the assembly of the Slave craton. Finally, to improve the efficiency and automation of receiver function calculation and data preprocessing workflow, I develop an application of an array-conditioned deconvolution technique for effectively processing large amounts of seismic array data. I demonstrate that this technique is readily applicable to teleseismic array data. This technique is especially effective in turning noisy traces from earthquakes with smaller magnitudes into usable data.
by Chin-Wu Chen.
Ph.D.
30
Schneider, Felix Michael [Verfasser]. « Imaging an Intra-continental Subduction in Central Asia with Teleseismic Receiver Functions / Felix Michael Schneider ». Berlin : Freie Universität Berlin, 2014. http://d-nb.info/1054341443/34.
Texte intégral
31
VanDecar, John Callaway. « Upper-mantle structure of the Cascadia subduction zone from non-linear teleseismic travel-time inversion / ». Thesis, Connect to this title online ; UW restricted, 1991. http://hdl.handle.net/1773/6804.
Texte intégral
32
Hammond, William Charles. « Dynamics, flow and melt content of the Southern East Pacific Rise upper mantle from teleseismic tomography / ». view abstract or download file of text, 2000. http://wwwlib.umi.com/cr/uoregon/fullcit?p9998033.
Texte intégralRésumé :
Thesis (Ph. D.)--University of Oregon, 2000.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 139-151). Also available for download via the World Wide Web; free to University of Oregon users.
33
Frassetto, Andrew Michael. « TELESEISMIC STUDIES OF THE NORTH AMERICAN CORDILLERA : EVALUATING THE CHANGING STRUCTURE, COMPOSITION, AND FABRIC AFTER SUBDUCTION ». Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195821.
Texte intégralRésumé :
The cessation of wide-scale subduction and orogenic compression during the early to mid-Cenozoic radically altered the North American Cordillera. This dissertation summarizes the results of three seismic studies, conducted in different regions of western North America, aimed at understanding how the structure and character of the crust and upper mantle relate to regions of post-subduction magmatism and persisting high elevations. Across the southern Basin and Range and Colorado Plateau teleseismic receiver functions show that only the Colorado Plateau contains thick crust commensurate with its high elevation. In contrast the southern Basin and Range has a relatively uniform crustal thickness of ~30 km, which is inadequate to support the high elevations of some of its metamorphic core complexes. We conclude that local variations in the density of the crust or upper mantle may support at least some high elevations in the southern Basin and Range. A large dataset of receiver functions collected across the Sierra Nevada show a complicated crust-mantle boundary which varies geographically, transitioning from thin crust beneath the eastern Sierra to thick crust underlying the western foothills. The thicker crust coincides with xenoliths sampling a remnant mafic-ultramafic residue produced during arc magmatism in the late Cretaceous. Modeling of receiver functions suggests that recent volcanism throughout the elevated eastern Sierra and nearby Basin and Range results from continued foundering of this dense material and its replacement with asthenosphere at relatively shallow depths in the upper mantle. In the Canadian Cordillera, regional observations of shear-wave splitting constrain the orientation and magnitude of seismic anisotropy. A pronounced and unusual trend of shear-wave splitting across the central British Columbia suggests that eastward directed flow of mantle asthenosphere fuels recent, widespread and geochemically distinct post-subduction volcanism within the northern slab window. These observations show how local and dynamic processes contribute to the support of lingering high elevations across western North America and that regions formerly associated with subduction may experience renewed magmatism due to inflow and subsequent melting of asthenospheric mantle.
34
Hosseini, Kasra [Verfasser], et Heiner [Akademischer Betreuer] Igel. « Global multiple-frequency seismic tomography using teleseismic and core-diffracted body waves / Kasra Hosseini. Betreuer : Heiner Igel ». München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1106854594/34.
Texte intégral
35
Heuer, Barbara. « Lithospheric and upper mantle structure beneath the western Bohemian Massif obtained from teleseismic P and S receiver functions ». Potsdam : Geoforschungszentrum [u.a.], 2006. http://www.diss.fu-berlin.de/2006/401/index.html.
Texte intégral
36
El-Haddadeh, B. R. H. « Seismological investigation of the crust and upper mantle structure of the British Isles using teleseismic travel time data ». Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372598.
Texte intégral
37
Schneider, Felix Michael [Verfasser]. « Imaging an intra-continental subduction in Central Asia with teleseismic receiver functions / Felix Michael Schneider. Deutsches GeoForschungsZentrum GFZ ». Potsdam : Deutsches GeoForschungsZentrum GFZ, 2014. http://nbn-resolving.de/urn:nbn:de:kobv:b103-14063.
Texte intégral
38
Dewberry, Shawn Robert. « Crustal and upper mantle structure for the Pacific Northwest from an analysis of short-period teleseismic network data / ». Thesis, Connect to this title online ; UW restricted, 1996. http://hdl.handle.net/1773/6795.
Texte intégral
39
Rößler, Dirk, Frank Krüger, Matthias Ohrnberger et Lutz Ehlert. « Automatic near real-time characterisation of large earthquakes ». Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2008/2019/.
Texte intégralRésumé :
An der Universität Potsdam wird seit 2008 ein automatisiertes Verfahren angewandt, um Bruchparamter großer Erdbeben in quasi-Echtzeit, d.h. wenige Minuten nachdem sich das Beben ereignet hat, zu bestimmen und der Öffentlichkeit via Internet zur Verfügung zu stellen. Es ist vorgesehen, das System in das Deutsch-Indonesische Tsunamifrühwarnsystem (GITEWS) zu integrieren, für das es speziell konfiguriert ist.
Wir bestimmen insbesondere die Dauer und die Ausdehnung des Erdbebens, sowie dessen Bruchgeschwindigkeit und -richtung. Dabei benutzen wir die Seismogramme der zuerst eintreffenden P Wellen vom Breitbandstationen in teleseimischer Entfernung vom Beben sowie herkömmliche Arrayverfahren in teilweise modifizierter Form. Die Semblance wir als Ähnlichkeitsmaß verwendet, um Seismogramme eines Stationsnetzes zu vergleichen. Im Falle eines Erdbebens ist die Semblance unter Berücksichtigung des Hypozentrums zur Herdzeit und während des Bruchvorgangs deutlich zeitlich und räumlich erhöht und konzentriert. Indem wir die Ergebnisse verschiedener Stationsnetzwerke kombinieren, erreichen wir Unabhängigkeit von der Herdcharakteristik und eine raum-zeitliche Auflösung, die es erlaubt die o.g. Parameter abzuleiten.
In unserem Beitrag skizzieren wir die Methode. Anhand der beiden M8.0 Benkulu Erdbeben (Sumatra, Indonesien) vom 12.09.2007 und dem M8.0 Sichuan Ereignis (China) vom 12.05.2008 demonstrieren wir Auflösungsmöglichkeiten und vergleichen die Ergebnisse der automatisierten Echtzeitanwendung mit nachträglichen Berechnungen.
Weiterhin stellen wir eine Internetseite zur Verfügung, die die Ergebnisse präsentiert und animiert. Diese kann z.B. in geowissenschaftlichen Einrichtungen an Computerterminals gezeigt werden. Die Internetauftritte haben die folgenden Adressen:
http://www.geo.uni-potsdam.de/arbeitsgruppen/Geophysik_Seismologie/forschung/ruptrack/openday
http://www.geo.uni-potsdam.de/arbeitsgruppen/Geophysik_Seismologie/forschung/ruptrack
40
Heit, Benjamin S. « Teleseismic tomographic images of the Central Andes at 21°S and 25.5°S an inside look at the Altiplano and Puna plateaus / ». [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2005/319/index.html.
Texte intégral
41
Beller, Stephen. « Imagerie lithosphérique par inversion de formes d’ondes télésismiques – Application aux Alpes Occidentales ». Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4007/document.
Texte intégralRésumé :
Dans cette thèse, un algorithme d'inversion de formes d'ondes (FWI) est développé pour l'imagerie 3D des paramètres élastiques de la lithosphère à partir des enregistrements télésismiques dans le but d'accroître la résolution des images lithosphériques. La modélisation sismique est effectuée par un méthode hybride d'injection de champ d'ondes. Une première modélisation est effectuée dans une Terre globale avec le logiciel AxiSEM pour déterminer les champs d’ondes aux bords de la cible lithosphérique. Ces solutions sont ensuite propagées dans cette cible par une méthode aux éléments finis spectraux. Le problème inverse est résolu avec un algorithme d’optimisation locale de type quasi-Newton (l-BFGS). La sensibilité de la méthode à la configuration expérimentale (paramétrisation du milieu, modèle initial, géométrie et échantillonnage du dispositif de capteurs) est tout d’abord analysée avec un modèle synthétique réaliste des Alpes Occidentales. L’algorithme est finalement appliqué à neuf événements de la campagne CIFALPS dans les Alpes occidentales jusqu’à une fréquence de 0.2Hz. Les modèles de vitesses P et S et de densité révèlent les grandes structures lithosphériques de la chaîne alpine, en particulier le corps d’Ivrée et la géométrie des Moho européen et adriatique. Plus profondément, deux anomalies de vitesses lentes sont imagées dans le manteau et sont interprétées comme la signature d’une remontée asthénosphérique et la localisation du détachement du panneau plongeant européen. Ces résultats corroborent l’hypothèse d’une subduction continentale de la croûte européenne et d’une éventuelle déchirure du panneau plongeant européen lors de la phase de collisionIn this thesis, a full-waveform inversion (FWI) algorithm is developed with the aim to image the elastic properties (Vp, Vs and density) of 3D lithospheric models from teleseismic recordings with a spatial resolution of the order of the wavelength. Seismic modeling is performed with a wavefield injection hybrid approach. A first simulation is performed in a global radially symmetric Earth with the AxiSEM code to compute the wavefields on the borders of the lithospheric target. Then, these wavefields are propagated in the target with the spectral finite-element method. After linearization, the inverse problem is solved with a quasi-Newton (1-BFGS) optimization algorithm. The sensitivity of the teleseismic FWI to the experimental setup (subsurface parameterization, initial model, sampling and geometry of the station layout) is first assessed with a realistic synthetic model of the Western Alps. The method is finally applied to nine events of the CIFALPS experiment carried out in the Western Alps, up to a frequency of 0.2Hz. Reliable models of P and S wave speeds and density reveal with an unprecedented resolution the crustal and lithospheric structures of the Alpine Belt, in particular the geometry of the Ivrea body, and the European and Adriatic Mohos. Deeper, two slow velocity anomalies beneath the Western Alps are imaged in the mantle. The first, to the west of the chain, is interpreted as the signature of an asthenospheric upwelling, the second near the location of the Ivrea body indicates the European slab break-off. The study supports the hypothesis of the European continental crust subduction and confirms the possible tearing of the European slab
42
Santos, Rúben José Chaves Miguel dos. « Modelação de processos de rotura sísmica através de dados de observação da deformação superficial ». Doctoral thesis, Universidade de Évora, 2013. http://hdl.handle.net/10174/11790.
Texte intégralRésumé :
Nesta dissertação foi desenvolvida uma metodologia baseada no cruzamento de diferentes
técnicas e de dados geodésicos e sísmicos, para estudar o processo de rotura de sismos.
A metodologia consiste, numa primeira fase, em determinar o campo de deslocamento
cossísmico produzido por um evento, através da técnica InSAR. Numa fase seguinte o
modelo de deslocamentos cossísmicos é determinado através das equações de Okada
utilizando o modelo de distribuição de deslizamentos obtido pela inversão das formas de onda
registadas em estações de banda larga a distâncias telessísmicas. Para comparar o modelo de
deslocamentos cossísmicos com o interferograma é aplicado um algoritmo que projeta os
deslocamentos do modelo na direção do satélite e de seguida procura a região homóloga entre
esse modelo e o interferograma, pelo cálculo da máxima correlação entre ambas as regiões,
que resulta também na relocalização da fonte. O processo de inversão/modelação da
deformação/comparação é repetido iterativamente até se conseguirem bons ajustes
simultaneamente nos dados sísmicos e geodésicos.
Esta metodologia foi aplicada no estudo dos sismos ocorridos a 12 de janeiro de 2010 no
Haiti; a 22 de fevereiro de 2006 em Moçambique; e a 21 de maio de 2003 na Argélia.
No estudo do sismo ocorrido no Haiti foi utilizado um par interferométrico do sensor ALOSPALSAR,
relativo à órbita descendente 447, onde foi medido o deslocamento máximo de ~70
cm na direção do satélite. O conjunto de 32 registos das formas de onda permitiu obter o
modelo de rotura e respetivos deslocamentos superficiais, para quatro soluções de parâmetros
da geometria da falha. Após a comparação entre os modelos de deslocamentos e o
interferograma é concluído que os parâmetros que melhor justificam a deformação observada
no interferograma são: a falha orientada segundo um azimute de 262º, com uma inclinação de
42º para norte e um rake médio de 42º.
No estudo do sismo de Moçambique foi usado um par interferométrico do satélite ENVISAT
e um conjunto de 36 registos telessísmicos. Desta forma foi possível concluir que a rotura
ocorreu na direção 165ºN numa falha com inclinação de 76º para oeste e os deslizamentos
ocorreram com um rake médio de 90º, sobre uma falha com um comprimento de 40.6 km por
29 km de largura. Neste modelo de rotura foi obtido o momento sísmico de 3.9x1019Nm, com
um deslizamento máximo de 4.1 m próximo do hipocentro. A modelação dos deslocamentos
cossísmicos representa bem os deslocamentos observados no terreno e medidos no
interferograma.
Para o estudo do sismo de Zemmouri-Boumedès foram utilizados alguns pares
interferométricos do satélite ENVISAT, as medições realizadas ao longo da costa da Argélia e
um conjunto de 28 registos das formas de onda. Os interferogramas revelaram uma fraca
coerência, mas mesmo assim foi possível observar 19 franjas (~53 cm) a oeste de Boumerdès.
Os parâmetros que justificam os deslocamentos cossísmicos são: strike=64º; dip=50º;
rake=97º. Este modelo permite gerar a sobre-elevação observada ao longo da costa, como a
configuração das franjas interferométricas. O plano desta solução localiza-se no mar, a 9 km
da linha de costa e o respetivo epicentro está localizado no mar; Modelling of active internal processes through observation data of
surface deformation.
### Abstract:
In this dissertation a methodology that consists of the cross of different techniques and
geodetic and seismic data, to study the earthquake rupture process was developed.
The methodology consists initially in determining the field of co-seismic displacements
caused by an event using the InSAR technique. In a next step the co-seismic displacements
model is determined by the equations of Okada using the model of rupture obtained from the
inversion of waveforms recorded in the broadband stations at teleseismic distances. To
compare the co-seismic displacement model with the interferogram is applied an algorithm
that project the model of the displacements toward the satellite and is then applied to search
the homologous region between the two region, which also results the re-location of the
source. The process of inversion/modeling of the deformation/comparison is repeated
iteratively until achieving good adjustments in both seismic and geodetic data.
This methodology was applied in the study of the earthquakes that occurred on January 12,
2010 in Haiti, on February 22, 2006 in Mozambique, and on May 21, 2003 in Algeria.
In the Haiti earthquake study an interferometric pair of the ALOS-PALSAR sensor of the
descending orbit 447 was used, where it was measured the maximum co-seismic
displacement of ~70 cm in the direction of the satellite. The set of 32 registers of the
waveforms allows obtaining the model of the rupture and the displacements on the earth
surface, for four solutions with different geometries parameters. After comparing the models
of the displacements with the interferogram is concluded that the parameters that better
explain the deformation observed in the interferogram is the fault azimuth of 262° with an
inclination of 42º north and the rupture occurred with an rake of 42º.
In the Mozambique earthquake study was used an interferometric pair of the ENVISAT
satellite and a set of 36 teleseismic registration. Thus it was concluded that the rupture
occurred with an azimuth of 165º North with an inclination of 76º westward, the slip occurred
with a rake of 90°, on a fault with a length of 40.6 km to 29 km wide. The seismic moment
obtained was 3.9x1019 Nm, the maximum slip was 4.1m near the hypocenter and the model of
the displacements is well fit to the co-seismic displacements observed on the coastline and in
the measurements in the interferogram.
To study the earthquake Zemmouri-Boumedès were used some interferometric pairs of the
ENVISAT satellite, the measurements along the coastline of Algeria and a set of 28 records
of waveforms. The interferograms revealed a low coherence, but it was still possible to
observe 19 fringes (~53 cm) west of Boumerdès. The parameters that better justify the coseismic
displacements are strike=64°, dip=50°, rake=97º. This model allows us to cause the
uplift observed along the coastline, such as the configuration of the interferometric fringes.
The plan of this solution is located at the sea, 9 km of coastline and also its epicenter is
located at the see.
43
Heuer, Barbara [Verfasser]. « Lithospheric and upper mantle structure beneath the western Bohemian Massif obtained from teleseismic P and S receiver functions / Geoforschungszentrum Potsdam in der Helmholtz-Gemeinschaft. Barbara Heuer ». Potsdam : Geoforschungszentrum, 2006. http://d-nb.info/98226769X/34.
Texte intégral
44
Kufner, Sofia-Katerina [Verfasser]. « Lithospheric structure and seismotectonic setting of the Hindu Kush, the Tajik-Afghan basin and the western Pamir from analysis of local- and teleseismic data / Sofia-Katerina Kufner ». Berlin : Freie Universität Berlin, 2016. http://d-nb.info/1122438737/34.
Texte intégral
45
Nooshiri, Nima [Verfasser], Torsten [Akademischer Betreuer] Dahm, Frederik [Akademischer Betreuer] Tilmann, Torsten [Gutachter] Dahm, Frank [Gutachter] Krüger et Steven J. [Gutachter] Gibbons. « Improvement of routine seismic source parameter estimation based on regional and teleseismic recordings / Nima Nooshiri ; Gutachter : Torsten Dahm, Frank Krüger, Steven J. Gibbons ; Torsten Dahm, Frederik Tilmann ». Potsdam : Universität Potsdam, 2020. http://d-nb.info/1218795182/34.
Texte intégral
46
Silvennoinen, H. (Hanna). « 3D structure of the crust and upper mantle beneath Northern Fennoscandian shield ». Doctoral thesis, University of Oulu, 2015. http://urn.fi/urn:isbn:9789526210681.
Texte intégralRésumé :
Abstract
The crustal and upper mantle structures of the Shield on the regional scale were
investigated using the data of the POLENET/LAPNET passive seismic array and
the previously published models of active and passive seismic experiments in the
study area. This area is centred in northern Finland and it extends to surrounding
areas in Sweden, Norway and northwestern Russia. The bedrock there is mostly of
the Archaean origin and the lithosphere of the region was reworked by two orogenies
during Palaeoproterozoic.
One of the results of the thesis was a new map of the Moho depth of the study area,
for which new estimates of the crustal thickness were obtained using receiver function
method and complemented by published results of receiver function studies and controlled
source seismic profiles. The map differs from the previously published maps in
two locations, where we found significant deepening of the Moho. The 3D structure of
the upper mantle was studied using teleseismic traveltime tomography method. The
resulting model shows high seismic velocities below three cratonic units of the study
area, which may correspond to non-reworked fragments of cratonic lithosphere and a
low velocity anomaly separating these cratonic units from each other.
The regional scale studies were complemented by two smaller scale studies in upper
crust level using combined interpretation of seismic profiling and gravity data. These
studies were centred on Archaean Kuhmo Greenstone Belt in eastern Finland and
central Lapland in northern Finland located in the crust reworked during Palaeoproterozoic.
Both areas are considered as prospective ones for mineral exploration. Both
studies demonstrate the advantage of gravity data inversion in studying 3D density
structure of geologically interesting formations, when the Bouguer anomaly data is
combined with a priori information from petrophysical and seismic datasets.
47
Moidaki, Moikwathai. « Crustal modification by tectonic events and upper mantle anisotropy beneath the Midcontinent Rift and New Madrid Seismic Zone : insights from receiver function studies and teleseismic shear wave splitting ». Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Moidaki_09007dcc8064a755.pdf.
Texte intégralRésumé :
Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 29, 2009) Includes bibliographical references (p. 119-131).
48
Läderach, Christine [Verfasser], Vera [Akademischer Betreuer] Schlindwein et Cornelia [Akademischer Betreuer] Spiegel. « Seismicity of ultraslow spreading mid-ocean ridges at local, regional and teleseismic scales : A case study of contrasting segments / Christine Läderach. Gutachter : Vera Schlindwein ; Cornelia Spiegel. Betreuer : Vera Schlindwein ». Bremen : Staats- und Universitätsbibliothek Bremen, 2012. http://d-nb.info/107215577X/34.
Texte intégral
49
Heit, Benjamin S. [Verfasser]. « Teleseismic tomographic images of the Central Andes at 21°S and 25.5°S : an inside look at the Altiplano and Puna plateaus / Geoforschungszentrum Potsdam, Stiftung des Öffentlichen Rechts. Benjamin S. Heit ». Potsdam : Geoforschungszentrum, 2006. http://d-nb.info/97980258X/34.
Texte intégral
50
Wang, Yi. « Imagerie haute résolution des structures lithosphériques par inversion de formes d'ondes P télésismiques courte période ». Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30018.
Texte intégralRésumé :
La tomographie sismique permet d'imager l'intérieur de la Terre à partir de l'observation des ondes sismiques faite à la surface. L'inversion de forme d'ondes complètes est une méthode tomographique qui permet d'imager les structures lithosphériques de petite échelle. Cette approche demande des méthodes numériques efficaces et précises pour résoudre l'équation des ondes dans des milieux hétérogènes complexes. En théorie, la limite de résolution que l'on peut atteindre avec cette technique est de l'ordre de grandeur de la plus petite longueur d'onde présente dans le champ d'onde utilisé. Du fait de son coût élevé en temps de calcul, l'inversion de formes d'ondes complètes constituait encore récemment un formidable défi pour le sismologue. Cependant, cette situation est en train d'évoluer rapidement du fait des progrès récents à la fois des moyens de calcul haute performance ainsi que des méthodes numériques, mais aussi des déploiements de réseaux denses à l'échelle régionale. Dans cette thèse, nous nous sommes intéressés à l'imagerie haute résolution des structures lithosphériques sous la chaine des Pyrénées par inversion de formes d'ondes P télésismiques courte période. L'objectif principal est d'apporter des contraintes nouvelles sur le taux de raccourcissement subi par cette chaine de montagnes pendant la convergence alpine. Nous utilisons une méthode de modélisation hybride qui couple une méthode de propagation d'onde globale 1D à une méthode d'éléments spectraux 3D à l'échelle régionale. Cette méthode hybride permet de coupler les champs globaux et régionaux sur les bords du domaine régional 3D. Elle limite les calculs 3D qui sont extrêmement couteux à l'intérieur du domaine régional, ce qui permet de réduire considérablement le temps de calcul. La méthode hybride permet ainsi de modéliser des sismogrammes synthétiques jusqu'à des périodes de l'ordre de la seconde, en prenant en compte toutes les complexités qui peuvent affecter la propagation des ondes dans le domaine régional 3D. A l'aide de cette méthode, il est également possible de calculer par la méthode de l'adjoint les dérivées de Fréchet qui relient les perturbations des formes d'onde observées aux perturbations des paramètres élastiques et de la densité dans le milieu. Ces noyaux de sensibilité sont utilisés pour formuler un problème inverse résolu par un algorithme itératif de type L-BFGS. Nous inversons les données de 5 sources télésismiques enregistrées par deux transects denses déployés au niveau des Pyrénées occidentales et centrales pendant l'expérience PYROPE. Nous avons ainsi obtenu les premières sections haute résolution de vitesses des ondes P et S au travers d'une chaine de montagnes. Les modèles tomographiques apportent des évidences claires en faveur d'un sous charriage de la plaque ibérique sous la plaque européenne. Ils montrent également l'importance de l'héritage et en particulier des structures liées à l'épisode de rifting crétacé dans la structuration de la chaineSeismic tomography allows us to image the Earth's interior based on surface observations of seismic waves. The full waveform inversion (FWI) method has the potential to improve tomographic images for the fine scale structures of the lithosphere. For this reason it receives a lot of attention of seismologists. FWI requires an efficient and precise numerical techniques to solve the elastic wave equation in 3D heterogeneous media. Its resolution potential is limited by the shortest wavelength in the seismic wavefield and the wavefield sampling density. Because of the high computational cost of modeling the propagation of seismic waves in heterogeneous media, FWI remains challenging. However, owing to the progress in high performance computational resources and numerical simulation techniques, as well as the deployment of permanent and temporary broadband arrays in the last two decades, this situation has changed dramatically. In this thesis, we focus on the high resolution imaging of lithospheric structure beneath the Pyrenean range by FWI, to quantify the highly controversial amount of convergence that occurred during the formation of this mountain range. In order to obtain finely resolved tomographic images, we exploit short period teleseismic P waves recorded by dense transects. We use a hybrid method that couples a global wave propagation method in a 1D Earth model to a 3D spectral-element method in a regional domain. A boundary coupling approach is used to match the global and regional wavefields on the boundaries of the regional domain. This hybrid method restricts the costly 3D computations inside the regional domain, which dramatically decreases the computational cost. The hybrid method can model teleseismic wavefields down to 1s period, accounting for all the complexities that may affect the propagation of seismic waves in the 3D regional domain. By using this hybrid method, the sensitivity kernels of the least square waveform misfit function with respect to elastic and density perturbations in the regional domain are computed with the adjoint state method. These waveform sensitivity kernels are used in an iterative L-BFGS algorithm to invert broad-band waveform data recorded by two dense transects deployed during the temporary PYROPE experiment across the Pyrenees mountains. We obtain the first high resolution lithospheric sections of compressional and shear velocities across the Pyrenean orogenic belt. The tomographic models provide clear evidence for the underthrust of the thinned Iberian crust beneath the European plate and for the important role of rift-inherited mantle structures during the formation of the Pyrenees