Την 8η Ιουνίου 2008, στις 15:25 τοπική ώρα (12:25 GMT) ένας σεισμός μεγέθους Mw 6.4 εκδηλώθηκε στη ΒΔ Πελοπόννησο, στη Δυτική Ελλάδα. Το επίκεντρο προσδιορίστηκε κοντά στο χωριό Μιχόι, στη Δημοτική Ενότητα Μόβρης, περίπου 35 km ΝΔ της Πάτρας. Στην παρούσα εργασία, έγινε μία μελέτη ανισοτροπίας στην επικεντρική περιοχή του σεισμού της 8ης Ιουνίου. Συγκεκριμένα, έγινε μία μελέτη για την ανίχνευση του φαινομένου διαχωρισμού των εγκαρσίων κυμάτων και της εξέλιξής του σε σχέση με την εκδήλωση του σεισμού της 8ης Ιουνίου. Χρησιμοποιήθηκαν οι καταγραφές από τον σεισμολογικό σταθμό του Ριόλου (RLS), καθώς είναι ο μόνος κοντινός σταθμός στο επίκεντρο του σεισμού της 8ης Ιουνίου που βρισκόταν σε συνεχή λειτουργία κατά τα χρονικά διαστήματα πριν και μετά την εκδήλωση του σεισμού. Για τη μελέτη του φαινομένου του διαχωρισμού των εγκαρσίων κυμάτων χρησιμοποιήθηκε η μέθοδος cross-correlation (Ando et al., 1983; Fukao, 1984). Μετά την επεξεργασία των δεδομένων, προσδιορίστηκαν οι παράμετροι του φαινομένου, φ (διεύθυνση ταλάντωσης της ταχύτερης συνιστώσας των εγκαρσίων κυμάτων) και dt (χρόνος καθυστέρησης μεταξύ των δύο συνιστωσών) για κάθε ένα σεισμικό γεγονός. Ο διαχωρισμός των εγκαρσίων κυμάτων (shear-wave splitting) είναι ένα φαινόμενο κατά το οποίο, τα εγκάρσια κύματα διαχωρίζονται σε δύο συνιστώσες, με διαφορετικές διευθύνσεις πόλωσης και διαφορετικές ταχύτητες διάδοσης. Ο διαχωρισμός αυτός πραγματοποιείται κατά την διάδοση των εγκαρσίων κυμάτων μέσα από ένα ανισοτροπικό μέσο (Crampin and Chastin, 2003; Crampin and Peacock, 2005). Σύμφωνα με τη θεωρία, ο διαχωρισμός των εγκαρσίων κυμάτων στον φλοιό, προκαλείται εξαιτίας της ύπαρξης μικρο-ρωγμών, μικρο-διαρρήξεων κορεσμένων με ρευστά. Οι μικρο-διαρήξεις αυτές έχουν συνήθως διευθύνσεις παράλληλες ή υπό-παράλληλες με αυτή της μέγιστης οριζόντιας συμπιεστικής τάσης σε μία περιοχή (Crampin, 1993). Η ανάλυση των δεδομένων κατέδειξε την ύπαρξη του φαινομένου διαχωρισμού των εγκαρσίων κυμάτων στην υπό μελέτη περιοχή. Τόσο πριν, όσο και μετά την εκδήλωση του σεισμού της 8ης Ιουνίου, οι διευθύνσεις πόλωσης της ταχύτερης συνιστώσας των εγκαρσίων κυμάτων ακολουθούν μία μέση διεύθυνση ΒΒΔ-ΝΝΑ. Η μέση διεύθυνση της ταχύτερης συνιστώσας δεν είναι σύμφωνη με τα χαρακτηριστικά του πεδίου των τάσεων στην περιοχή, όπως προσδιορίστηκαν από τους Konstantinou et al. (2011) και Hollenstein et al. (2008), με μία μέση διεύθυνση οριζόντιας συμπιεστικής τάσης Α-Δ. Η ΒΒΔ-ΝΝΑ διεύθυνση πόλωσης της ταχύτερης συνιστώσας οφείλεται πιθανόν στη δράση ενός πεδίου τάσεων γύρω και κάτω από τη θέση καταγραφής με τοπικά χαρακτηριστικά. Τέλος, παρατηρήθηκε μία αύξηση στις τιμές των χρόνων καθυστέρησης μετά την εκδήλωση του σεισμού της 8ης Ιουνίου. Η μέση τιμή των χρόνων καθυστέρησης πριν την εκδήλωση του σεισμού ήταν περίπου 27.3 ms, ενώ μετά την εκδήλωσή του 41.7 ms. H αύξηση των χρόνων καθυστέρησης, υποδηλώνει μία μεταβολή των ιδιοτήτων του μέσου στον ανώτερο φλοιό εξαιτίας της εκδήλωσης του σεισμού. Η εκδήλωση του σεισμού της 8ης Ιουνίου προκάλεσε πιθανόν την διεύρυνση και την επιμήκυνση των προϋπαρχόντων μικρο-διαρρήξεων του φλοιού, τη δημιουργία νέων και την επιπλέον πλήρωσή τους με ρευστά. / On June 8, 2008, at 15:25 local time (12:25 GMT) an Mw 6.4 earthquake occurred in the area of northwest Peloponnesus, Western Greece. The epicenter was located near Mihoi village, in the municipality of Movri, about 35 km southwest of Patras. In this paper, a crustal anisotropy analysis was performed in the epicentral area of Movri Mountain earthquake. Specifically, there was a study to detect shear-wave splitting phenomenon and its temporal evolution in relation to the occurrence of Movri Mountain earthquake. For the needs of the study, we used seismic records from the seismological station of Riolos (RLS). Riolos station is the nearest station from the epicenter of Movri Mountain earthquake which was in continuous operation during the periods before and after the occurrence of the earthquake. The method that was used to study shear-wave splitting phenomenon was the cross-correlation method (Ando et al., 1983; Fukao, 1984; Kuo et al., 1994). Through the data processing, splitting parameters φ (polarization direction of the fastest component of shear waves) and dt (time delay between the two components) were measured for each seismic event. Shear-wave splitting is a phenomenon in which shear-waves are separated into two components with different polarization directions and velocities. The phenomenon in the upper crust is caused by the existence of stress-aligned, fluid-filled micro-cracks/micro-fractures. The polarization directions of the fast components are usually parallel or sub-parallel to the direction of the maximum horizontal compressive stress (Crampin, 1993). Data analysis revealed the existence of shear-wave splitting phenomenon in the study area. Both before and after the occurrence of Movri Mountain earthquake, the polarization directions of the fast component of shear waves follow a general NNW-SSE direction. The observed mean fast polarization direction is not consistent with the estimated characteristics of the regional stress field of the broader area, as identified by Kontsantinou et al. (2011) and Hollenstein et al. (2008), who report a general E-W direction of the maximum horizontal compressive stress. The difference between the estimated fast polarization directions and the properties of the regional stress field shows the presence of a local stress field in the study area. Finally, an increase in time delays was observed after the occurrence of Movri Mountain earthquake. The average value of delay times before the occurrence of the earthquake was about 27.3ms, while after the occurrence was about 41.7ms. The increase in delay times which was observed after the occurrence of Movri Mountain earthquake possibly indicates changes in the properties of the medium in the upper crust. The occurrence of Movri Mountain earthquake caused the expansion/ lengthening of micro-cracks and its further filling with fluids.

Seismic anisotropy at continental regions, mainly at stable areas, gives important information about past and present tectonic events, and helps us in understanding patterns of upper mantle flow in a way not achieved by other methods. The measurement of shear wave splitting (SWS), at individual stations, from core refracted phases (such as SKS phases), indicates the amount and orientation of the seismic anisotropy in the upper mantle. Previous studies of SWS in South America concentrated mainly along the Andes and in southeast Brazil. Now we add extra measurements extending to all Brazilian territory, especially in the Pantanal and Paraná-Chaco basins, as part of the FAPESP 3-Basins Thematic Project. The results from both temporary deployments and from the Brazilian permanent network provide a more complete and robust anisotropy map of the South America stable platform. In general the fast polarization orientations have an average E-W orientation. Significant deviations to ESE-WNW or ENE-WSW are observed in many regions. We compare our results with different anisotropy proxies: absolute plate motion given by the hotspot reference frame HS3-NUVEL-1A, a recent model of time dependent upper mantle flow induced by the Nazca plate subduction, global anisotropy from surface wave tomography, and geologic trends. We observe a poor correlation of the anisotropy directions with geological trends, with the exception of a few stations in northern Brazil and a better correlation with the mantle flow model. Therefore, our observed anisotropy is mainly due to upper-mantle flow, with little contribution from frozen lithospheric anisotropy. Also, deviations from the mantle flow model, which includes a thicker lithosphere at the Amazon craton, are mainly due to flow surrounding cratonic nuclei not used in the model: the keel of the São Francisco craton and a possible cratonic nucleus beneath the northern part of the Paraná Basin (called Paranapanema block). Large delay times at the Pantanal Basin may indicate a stronger asthenospheric channel, a more coherent flow, or a thicker asthenosphere. Small delays beneath the northern Paraná Basin and central Amazon craton may indicate thinner anisotropic asthenosphere. / Anisotropia sísmica em regiões continentais, principalmente em áreas estáveis, nos dá informações importantes sobre eventos tectônicos do passado e do presente, e nos ajuda a entender padrões de fluxo do manto superior de forma não alcançada por outros métodos geofísicos. A medida de separação de ondas cisalhantes (SWS), em estações individuais, de fases refratadas no núcleo (fases SKS, por exemplo), indica a intensidade e orientação da anisotropia sísmica no manto superior. Estudos prévios de SWS na América do Sul se concentraram principalmente ao longo dos Andes e no sudeste do Brasil. Agora adicionamos medidas extras que se extendem por todo território Brasileiro e alguns países vizinhos, especialmente nas bacias do Pantanal e do Chaco-Paraná, como parte do \"Projeto Temático 3-Bacias\" da FAPESP. Os resultados tanto das estações temporárias quanto da rede permanente Brasileira mostram um mapa de anisotropia mais robusto e completo da plataforma estável da América do Sul. Em geral, as direções de polarização rápida tem em média direção L-O. Desvios significantes nas direções LSL-ONO ou LNL-OSO são observadas em muitas regiões. Comparamos nossos resultados com diferentes representantes da anisotropia: movimento absoluto de placa dado pelo sistema de referência de hotspot HS3-NUVEL-1A, um modelo recente dependente do tempo de fluxo do manto superior induzido pela subducção da placa de Nazca, anisotropia global de tomografia de ondas de superfície, e tendências geológicas. Observamos pouca correlação das direções de anisotropia com tendências geológicas, com exceção de algumas estações no norte do Brasil e uma melhor correlação com o modelo de fluxo do manto. Portanto, nossa anisotropia observada é devida principalmente a fluxo do manto superior, com pouca contribuição de anisotropia \"congelada\" litosférica. Também, desvios do modelo de fluxo do manto, o qual inclui uma litosfera mais espessa no cráton da Amazônia, são devido ao fluxo ao redor de núcleos cratônicos não usados no modelo: a quilha do cráton do São Francisco e um possível núcleo cratônico abaixo da região norte da bacia do Paraná (chamado bloco do Paranapanema). Atrasos de tempo grandes na bacia do Pantanal podem indicar um canal astenosférico mais forte, um fluxo mais coerente ou uma astenosfera mais espessa. Pequenos atrasos abaixo da parte norte da bacia do Paraná e no centro do cráton da Amazônia podem indicar uma astenosfera mais fina.

Seismic anisotropy at continental regions, mainly at stable areas, gives important information about past and present tectonic events, and helps us in understanding patterns of upper mantle flow in a way not achieved by other methods. The measurement of shear wave splitting (SWS), at individual stations, from core refracted phases (such as SKS phases), indicates the amount and orientation of the seismic anisotropy in the upper mantle. Previous studies of SWS in South America concentrated mainly along the Andes and in southeast Brazil. Now we add extra measurements extending to all Brazilian territory, especially in the Pantanal and Paraná-Chaco basins, as part of the FAPESP 3-Basins Thematic Project. The results from both temporary deployments and from the Brazilian permanent network provide a more complete and robust anisotropy map of the South America stable platform. In general the fast polarization orientations have an average E-W orientation. Significant deviations to ESE-WNW or ENE-WSW are observed in many regions. We compare our results with different anisotropy proxies: absolute plate motion given by the hotspot reference frame HS3-NUVEL-1A, a recent model of time dependent upper mantle flow induced by the Nazca plate subduction, global anisotropy from surface wave tomography, and geologic trends. We observe a poor correlation of the anisotropy directions with geological trends, with the exception of a few stations in northern Brazil and a better correlation with the mantle flow model. Therefore, our observed anisotropy is mainly due to upper-mantle flow, with little contribution from frozen lithospheric anisotropy. Also, deviations from the mantle flow model, which includes a thicker lithosphere at the Amazon craton, are mainly due to flow surrounding cratonic nuclei not used in the model: the keel of the São Francisco craton and a possible cratonic nucleus beneath the northern part of the Paraná Basin (called Paranapanema block). Large delay times at the Pantanal Basin may indicate a stronger asthenospheric channel, a more coherent flow, or a thicker asthenosphere. Small delays beneath the northern Paraná Basin and central Amazon craton may indicate thinner anisotropic asthenosphere. / Anisotropia sísmica em regiões continentais, principalmente em áreas estáveis, nos dá informações importantes sobre eventos tectônicos do passado e do presente, e nos ajuda a entender padrões de fluxo do manto superior de forma não alcançada por outros métodos geofísicos. A medida de separação de ondas cisalhantes (SWS), em estações individuais, de fases refratadas no núcleo (fases SKS, por exemplo), indica a intensidade e orientação da anisotropia sísmica no manto superior. Estudos prévios de SWS na América do Sul se concentraram principalmente ao longo dos Andes e no sudeste do Brasil. Agora adicionamos medidas extras que se extendem por todo território Brasileiro e alguns países vizinhos, especialmente nas bacias do Pantanal e do Chaco-Paraná, como parte do \"Projeto Temático 3-Bacias\" da FAPESP. Os resultados tanto das estações temporárias quanto da rede permanente Brasileira mostram um mapa de anisotropia mais robusto e completo da plataforma estável da América do Sul. Em geral, as direções de polarização rápida tem em média direção L-O. Desvios significantes nas direções LSL-ONO ou LNL-OSO são observadas em muitas regiões. Comparamos nossos resultados com diferentes representantes da anisotropia: movimento absoluto de placa dado pelo sistema de referência de hotspot HS3-NUVEL-1A, um modelo recente dependente do tempo de fluxo do manto superior induzido pela subducção da placa de Nazca, anisotropia global de tomografia de ondas de superfície, e tendências geológicas. Observamos pouca correlação das direções de anisotropia com tendências geológicas, com exceção de algumas estações no norte do Brasil e uma melhor correlação com o modelo de fluxo do manto. Portanto, nossa anisotropia observada é devida principalmente a fluxo do manto superior, com pouca contribuição de anisotropia \"congelada\" litosférica. Também, desvios do modelo de fluxo do manto, o qual inclui uma litosfera mais espessa no cráton da Amazônia, são devido ao fluxo ao redor de núcleos cratônicos não usados no modelo: a quilha do cráton do São Francisco e um possível núcleo cratônico abaixo da região norte da bacia do Paraná (chamado bloco do Paranapanema). Atrasos de tempo grandes na bacia do Pantanal podem indicar um canal astenosférico mais forte, um fluxo mais coerente ou uma astenosfera mais espessa. Pequenos atrasos abaixo da parte norte da bacia do Paraná e no centro do cráton da Amazônia podem indicar uma astenosfera mais fina.

xv, 136 p. : ill. (some col.) / The Pacific Northwest of the United States has been tectonically and magmatically active with the accretion of the Farallon oceanic terrane "Siletzia" ∼50 Ma. The accretion of Siletzia terminated the flat-slab subduction of the Farallon slab and initiated the Cascadia subduction zone. In this dissertation, I focus on both the large-scale tectonic structures preserved seismically in the crust and upper mantle, and the small-scale, short-term aseismic processes on the plate interface. I measure the shear-wave splitting trends around eastern Oregon with a dataset of ∼200 seismometers from 2006-2008 to analyze the upper-mantle anisotropy. The delay times between splitted shear-waves range from 0.8 s to 2.7 s. In the High Lava Plains, the fast polarization direction is approximately E-W with average delay time ∼1.8 s. I infer that there must be significant active flow in a roughly E-W direction in the asthenosphere beneath this area. The splitting pattern is more variable and complicated in NE Oregon, where the crust and mantle lithosphere may be a significant contribution. In terms of the imaged seismic velocity structures, I infer that the Eocene sedimentary basins in south-central Washington lie above a magmatically underplated crust of extended Siletzia lithosphere. Siletzia thrusts under the pre-accretion forearc, and its southeast termination is especially strong and sharp southeast of the Klamath-Blue Mountains gravity lineament. Magmatic intrusion has increased upper crustal velocity as in the less active Washington Cascades, but the higher temperatures beneath the magmatically active Oregon Cascades have a dominating effect. To better understand the physical mechanism of slow slip events on the plate interface, I explore the scaling relationships of various source parameters collected mainly from subduction zones worldwide and also other tectonic environments. The source parameter scaling relationships of slow slip events highlight the similarities and differences between slow slip phenomena and earthquakes. These relationships hold implications for the degree of heterogeneity and fault healing characteristics. The recurrence statistics of northern Cascadia events behave weakly time predictable and moderately anti-slip predictable, which may indicate healing between events. This dissertation includes co-authored materials both previously published and submitted for publication. / Committee in charge: Eugene Humphreys, Chairperson; David Schmidt, Member; Ray Weldon, Member; James Isenberg, Outside Member