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Ο Ελλαδικός χώρος είναι μεγάλου τεκτονικού και σεισμολογικού ενδιαφέροντος. Ιδιαίτερα η ΒΔ Πελοπόννησος που αποτελεί μια από τις πιο ενεργές σεισμικά περιοχές της Ευρώπης και του πλανήτη. Στην παρούσα εργασία έγινε επεξεργασία μικροσεισμικών δεδομένων από τους μετασεισμούς (15/09/2008 – 08/10/2008) του σεισμού της Μόβρης (8η Ιουνίου 2008) με σκοπό την ανάλυση της μετασεισμικής ακολουθίας και την παρουσίαση των σεισμοτεκτονικών χαρακτηριστηκών της ΒΔ Πελοποννήσου. Στα πλαίσια της εργασίας δημιουργήθηκαν χάρτες και διαγράμματα με κατανομή επικέντρων και τα χαρακτηριστικά των συμβάντων αντίστοιχα. / The area of Greece is highly active seismically. NW Peloponnese is one of the most active areas of Europe and the earth. In this study data from the aftershocks of Movri earthquake (8 June 2008) are used to describe the tectonic enviroment of Peloponnese. Maps created in this study and histograms display the conclusions. The aftershocks used were from 15/09/2008 until 08/10/2008.

La partie orientale de la Méditerranée, est une des régions sismiques les plus actives en Europe. La présence dans cette région de nombreux lacs et bassins marins isolé fait de cette région un endroit idéal pour étudier l'enregistrement de l'activité sismo- tectonique et les principaux changements climatiques dans des environnements subaquatiques. Dans cette thèse, nous nous intéressons à l'étude de l'enregistrement paléosismique subaquatique du Quaternaire tardive dans deux bassins: la Mer de Marmara et le Golfe de Corinthe. Ces derniers sont des bassins marins isolés traversés par des failles majeures (par exemple, la faille Nord Anatolienne). Nous nous sommes concentrés sur l'identification des traces laissées par des paléoséismes dans l'enregistrement sédimentaire, en particulier, les couches nommées ici: "homogenites + turbidites" (HmTu), lequel représentent des événements sédimentaires quasi instantanés induits par des secousses sismiques. Leur identification a été réalisée à partir des analyses sédimentologiques classiques et des propriétés magnétiques, en particulier, l'anisotropie de la susceptibilité magnétique. Les analyses ont été effectuées sur les sédiments carottés à l'aide du système géant à piston CALYPSO. Ces sédiments représentent les dernières 17 cal ka BP de sédimentation, et ont enregistré le dernier passage de conditions non marine à des conditions marines. Dans la mer de Marmara, ce passage a été identifié autour de 12,8 cal ka BP, tandis que, dans le golfe de Corinthe était d'environ 11,7 cal ka BP. Dans les deux bassins, l'enregistrement des événements instantanés considérés comme induits par des séismes a permis l'estimation d'un intervalle moyen de récurrence. Dans le bassin de Çınarcık de la mer de Marmara, l'intervalle de récurrence moyenne minimale varie entre ~155 et ~365 ans, tandis que pour la partie orientale du golfe de Corinthe, l'intervalle de récurrence moyenne minimale varie entre ~400 et ~500 ans. Enfin, dans le bassin central de la mer de Marmara, l'étude des événements HmTu corrélées sur les côtés opposés d'un segment de la faille nord-anatolienne permet d'estimer le décalage vertical co-sismique pour une période continue de 2 ka. Des valeurs significatives observées étaient des décalées verticalement (jusqu'à 144 cm), ce qui implique un déplacement verticalement dominant (normal) pour ce segment. / The Eastern Mediterranean is one of most seismically active and rapidly deforming regions in Europe. The presence in this region of numerous lakes and isolate marine basins makes this region an ideal area to study the record of the seismo-tectonic activity and the main climatic changes in sub-aquatic environments. In this thesis we are interested in studying the Late Quaternary sub-aquatic paleoseismic record of two basins: The Sea of Marmara and The Gulf of Corinth. Both are isolated deep marine basins, crossed by major faults (e.g. the North Anatolian Fault). We focused on identifying the traces left by paleoearthquakes in the sedimentary record, particularly, the layers named here: “homogenites+turbidites” (HmTu), which represent individual sedimentary seism-induced events. Their identification was performed through classical sedimentological analyzes and magnetic properties, in particular the Anisotropy of Magnetic Susceptibility. Analyzes were conducted on sediment recovered by long Calypso piston cores. These sediments represent the last 17 cal kyr BP of sedimentation, and have recorded the last non-marine to marine change. In the Sea of Marmara, this passage was identified around 12.8 cal kyr BP, whereas in the Gulf of Corinth was around 11.7 cal kyr BP. In both basins, the record of the earthquake induced instantaneous events allowed the estimation of the average earthquake recurrence interval. In the Çinarcik Basin of the Sea of Marmara, the minimum average recurrence interval varies between ∼155 and 365 yr, while for the eastern part of the Gulf of Corinth the minimum average recurrence interval varies between ∼400 and ∼500 yr. Finally, in the Central Basin of the Sea of Marmara, the study of correlated HmTu events at opposite sides of a segment of the North Anatolian Fault allows the estimation of the co-seismic vertical offset for a continuous period of 2 kyr. Significant values of vertical offset were observed (up to 144 cm), implying a dominant vertical (normal) throw for this fault segment.

Dans l'histoire de l'Equateur, les séismes ont causé beaucoup de victimes (~60 000) et de nombreux autres problèmes. Les événements récents de la fin du XXe siècle ont mis en évidence que les constructions existantes présentent une vulnérabilité physique importante et que l'impact économique des tremblements de terre pourrait être très élevé. Le risque sismique a trois composantes principales : l'aléa, la vulnérabilité et l'exposition. Par conséquent, pour réduire le risque en Equateur, il est primordial d'effectuer des évaluations probabilistes de l'aléa sismique (PSHA).La première étape du développement du PSHA fut de construire un catalogue sismique dans lequel la sismicité historique et instrumentale est homogène et complète. Les données de sismicité instrumentale ont été rassemblées à partir des catalogues locaux et internationaux. Les événements ont été identifiés et, par l'utilisation d'un régime de hiérarchisation des endroits les plus fiables et des estimations de magnitude, les événements ont été regroupés dans un catalogue unique, unifié et homogénéisé. La sismicité historique réévaluée a ensuite été ajoutée. Le catalogue des séismes en Equateur entre 1587 et 2009 comprend ainsi 10 823 événements instrumentaux et 32 séismes historiques, avec une gamme de magnitude Mw de 3,0 à 8,8.Un modèle de zonage des sources sismiques (SSZ) a ensuite été effectué. Dans le cadre de cette modélisation, une nouvelle vision de la géodynamique de l'Équateur a été conçue. Deux aspects des interactions des plaques à l'échelle continentale permettent d'expliquer plusieurs caractéristiques observées dans la génération des tremblements de terre observés, comme l'essaim sismique d'El Puyo, ainsi que le couplage inter-sismique : les différences de rhéologie des plaques Nazca et Farallon et la convergence oblique provoquée par la forme convexe de la partie nord-ouest de la marge continentale sud-américaine. La paléomarge en extension Grijalva (GRM) marque la frontière entre les deux plaques. La sismicité et le couplage inter-sismique sont faibles et peu profonds au sud de la GRM et augmente vers le nord, avec un modèle de couplage hétérogène associé localement à la subduction de la ride de Carnegie. De grands séismes de décrochement ont rompu l'interface entre la ride de Carnegie et le nord. Au niveau continental, la frontière entre le bloc NA et le bloc stable Amérique du Sud est constituée par le système CCPP de failles. Il concentre la majorité de la libération du moment sismique dans la croûte Equateur. 19 SSZ ont été modélisées : une tranche-externe, trois interfaces, six intra-plaques et neuf croûtes.Le catalogue sismique et une version préliminaire du modèle SSZ ont été appliqués pour déterminer le PSH à Quito et évaluer les incertitudes. La ville est construite sur le toit d'un système de failles inverses actif, qui se déplace de 4,3 à 5,3 mm/an. Les PSH ont montré que la contribution de la SSZ locale explique presque entièrement l'aléa correspondant à une période de retour (PR) de 475 ans. L'analyse a donc été concentrée sur cette zone. La source locale, la géométrie de la SSZ, la modélisation des distributions de fréquence-magnitude et/ou de taux de glissement avec des pourcentages de verrouillage variables, la sélection des GMPEs et l'intégration de l'effet du compartiment chevauchant ont apporté des accélérations avec cette PR avec une variabilité importante. Le PGA moyen obtenu sur un site au rocher est ~0,4g avec cette PR, avec une variabilité de 0,3 à 0,73g.La mise à disposition du PSHA est cruciale pour la gestion des risques mais est compliquée, car les probabilités et les incertitudes ne sont pas facilement assimilées par la société. Suite aux pratiques des sciences sociales et les expériences acquises des alertes précoces d'éruption, une approche participative a été exposée pour construire collectivement des connaissances sur le risque de séisme à Quito, qui pourrait prendre la forme d'un observatoire citoyen. / Seismic hazard and risk are high in Ecuador. Earthquakes are notorious in history both for the number of victims (~60.000) and the hardships they have brought. Moreover, late 20th century events have highlighted evidences that the physical vulnerability of present-day buildings is considerable and that the economic impact of earthquakes could be devastating for Ecuador's sustained growth. Therefore, it is an important contribution for reducing the seismic risk to construct methodologically sound models for probabilistic seismic hazard assessment, which is the main objective of this dissertation.The first step was to construct a seismic catalog for the country where historical and instrumental seismicity is homogeneous and complete. The instrumental seismicity available in local and international catalogs since the beginning of the 20th century was collected. Events were singularized and, by means of a prioritizing scheme of most reliable locations and magnitude estimations, individual events were merged in a single, unified and homogenized catalog. Previously re-evaluated historical seismicity was appended. The 1587–2009 Ecuadorian earthquake catalog finally comprises 10,823 instrumental events plus 32 historical earthquakes with a Mw magnitude range from 3.0 to 8.8.Next a seismic source zones (SSZ) model for probabilistic seismic hazard analysis was worked out. In the course of modeling the SSZ, a new view of Ecuador's complex geodynamics was conceived. This view emphasizes two aspects of the plates' interactions at continental scale: the differences in rheology of Farallon and Nazca plates and the convergence obliquity resulting from the convex shape of the South American northwestern continental margin. Both conditions satisfactorily explain several characteristics of the observed earthquake generation –such as the El Puyo seismic cluster– as well as the interseismic coupling. The Grijalva rifted margin (GRM) marks the boundary between the two plates. Seismicity and interseismic coupling are weak and shallow south of the GRM and increases northward, showing a heterogeneous coupling pattern locally associated to Carnegie ridge's subduction. Great thrust earthquakes have ruptured the interface from Carnegie to the north, not breaking through Carnegie. In the continental realm the CCPP localized fault system constitutes the boundary between the NA block and stable South America. It concentrates most of the seismic moment release in crustal Ecuador. 19 SSZs have been modeled accounting for this new scheme: 1 outer-trench, 3 interface, six intraplate and 9 crustal.The catalog and a preliminary version of the SSZ model were applied in determining the PSH in Quito and assessing the uncertainties. The city is built on the hanging wall of an active reverse fault system that is moving at 4.3-5.3 mm/yr. PSH estimates showed that hazard levels at 475 years return period (RT) almost entirely proceed from the contribution of the local SSZ, therefore the analysis was concentrated on it. Significant variability in accelerations at that RT resulted from a variety of considerations: modeling the local source either as a zone or as fault source, the geometry of the SSZ, the way frequency-magnitude distributions and/or slip rates with variable locking percentages were modeled, the GMPEs selection and the inclusion of the hanging wall effect. The PGA mean value obtained for a rock site Quito is ~0.4 g in that RT with variability ranging from 0.3 to 0.73g.PSHA communication is crucial for risk management, but is difficult since probabilities and uncertainties are not easily assimilated by society. Following the practices of the social sciences and of experiences acquired in issuing eruption early warnings to rural communities, a participatory approach has been outlined to collectively build up knowledge about the earthquake risk in Quito that could take the form of a citizens' observatory for seismic risk awareness and reduction.

Tsunami hazards were greatly underestimated along the coasts of countries bordering the northeastern Indian Ocean until the occurrence of the 26 December 2004, Mw 9.2 earthquake and its ensuing tsunami. Sourced off the coast of northern Sumatra, on the plate boundary between the Indo-Australian and Eurasian plates, the rupture of the 2004 earthquake propagated ~1300 km northward. The magnitude of this earthquake and the reach of its tsunami exceeded all known precedents, based on instrumental and historic records. The coseismic deformational and post-tsunami depositional features facilitated opportunities to conduct tsunami geology studies along the coasts of countries bordering the Indian Ocean. Several questions are being posed, the answers of which have implications for tsunami hazard assessment. How did this plate boundary behave prior to and after the great earthquake? Was the 2004 earthquake the first of its kind on the Sumatra-Andaman plate boundary? If it had a predecessor, when did it occur and was it a true predecessor in terms of its rupture dimensions and tsunamigenic potential? What types of depositional evidence are preserved and how can we use them to develop the history of past tsunamigenic earthquakes? Researchers are exploring the affected regions and using the imprints left by the 2004 event, to address these questions. There are two components to this study: one, a seismotectonic analysis of the region from the perspective of plate driving forces and their relative roles in the interseismic and post-seismic phases. This study uses global data catalogs like the NEIC PDE (National Earthquake Information Centre Preliminary Determination of Epicenters) and the Global Centroid Moment Tensor (CMT) solutions for earthquake source parameters to understand the along-strike variations in seismicity patterns before and after the 2004 earthquake. The 2004 experience was unprecedented in South Asia. Unaffected by tsunami hazards in the past, tsunami geology is a nascent field for most South Asian researchers. Very little background field data is available on the deformational features of great earthquakes along this plate boundary and the depositional characteristics of extreme coastal surges, such as tsunamis and storms. Where do we begin our search for evidence of past tsunamigenic earthquakes? How best can we use the 2004 tsunami and its deposits as a proxy? What problems are encountered in the interpretations? This thesis addresses these questions in part and presents observations from the Andaman Islands (the ~400 km, northern segment of the Sumatra-Andaman subduction zone) and the southeast coast of India, towards developing a reliable database of tsunami geology for 2004-type events. The premise is that regions affected by the 2004 earthquake are more likely to conserve signatures from older events. Based on the stratigraphic context of the proxy and quality of age estimates, this work presents evidence for past earthquake related deformation and tsunami deposition. In this work we use deformational and depositional features from the Andaman Islands, falling within the 2004 rupture zone and from one location on the Tamil Nadu coast of India (Kaveripattinam). From a perceptive understanding of the features related to tectonic deformation of the Sumatra-Andaman subduction zone, we have selected the Andaman segment that demonstrates explicit evidence for deformation and tsunami deposition through geomorphological and stratigraphic features, which are key to our exploration. A gist of each chapter is given below. The introduction (chapter 1) presents the background, motivation and scope of this work and the organization of this thesis, also summarizing the contents of each chapter. Chapter 2 provides a review of literature on subduction zone earthquakes and updates on tsunami geology, to place this study in the global context. The next two chapters discuss the seismotectonics of the Sumatra-Andaman plate boundary, the important earthquakes and their source processes. In chapter 3 we discuss the Andaman segment (from 10–15° N), characterized by relatively lower level seismicity, but distinctive, as it falls within the northern limit of the 2004 rupture. The deformational and depositional features here are better exposed due to availability of land straddling the hinge line separating the areas of 2004 uplift and subsidence. Here, the pre-2004 earthquakes used to occur along a gently dipping subducting slab, up to a depth of about 40 km. Post-2004, the earthquakes moved up-dip, extending also to the outer-rise and outer-ridge regions, expressing post-earthquake relaxation [Andrade and Rajendran, 2011]. The southern Nicobar segment (5–10° N) differs from the Andaman segment in its style of deformation and seismic productivity. The decreasing obliquity of convergence, the likely influence of a subducting ocean ridge on the subducting plate and the character of the subducting oceanic plate make this segment distinctly different. In chapter 4 we present an analysis of its seismotectonic environment based on the well-constrained focal mechanisms of historic and recent earthquakes. We report that left-lateral strike-slip faulting on near N-S oriented faults control the deformation and the style of faulting is consistent to ~80 km within the subducting slab [Rajendran, K. et al., 2011]. The 11 April 2012 sequence of earthquakes on the subducting oceanic plate, between the Sumatra Trench and the Ninety East Ridge are the more recent among the oceanic intraplate earthquakes that demonstrate the reactivation of N-S oriented fossil fractures. The limited availability of land and the 2004 coseismic deformation dominated by subsidence, followed by prolonged waterlogging makes exploration difficult in the Nicobar segment. Thus, we focus on the Andaman Islands for deformational and depositional evidence, using observations that can be corroborated through multiple proxies and depositional environments that are not prone to other coastal surges, such as cyclones and storms. The criteria for selection of sites, evaluation of deposits and determination of limiting ages are discussed in chapters 5 through 9. In chapter 5 we discuss different types of coastal environments and their response to high-energy sea surges. We also give a brief review of the comparative analyses of storm and tsunami deposits, a highly debated issue and then discuss important characteristics of these two deposits, using examples from the 2004 tsunami and the 2011 Thane cyclone that affected parts of the Tamil Nadu coast. An important component of tsunami geology is the ability to identify and select datable material from tsunami deposits and chose an appropriate method for dating (chapter 6). The types of material used vary from peat layers, peat-rich soil, gastropod shells, wood, charcoal, organic remains such as bones, coral fragments, pottery sherds and buried soil. Techniques such as AMS Carbon-14 and Thermoluminescence are commonly used with appropriate calibrations and corrections. In addition to the dates generated in this study (based on wood and shell dates) we use some previous dates from the entire stretch of the rupture within the Indian Territory and assign a relative grading to these ages, based on the quality criterion evolved in this study. We believe that this is the first attempt to segregate age data obtained from coastal deposits, and assign them a specific quality grading based on their environment of deposition and the type of material dated. Chapter 7 presents results of our investigations in the Andaman Islands, which cover ~30% of the rupture area. A coseismically subsided mangrove from Rangachanga (Port Blair, east coast of South Andaman) led us to a former subsidence during AD 770–1040, which we believe is the most convincing evidence for a previous tectonic event. Data based on inland deposits of coral and organic debris yielded a younger age in the range of AD 1480–1660. Both these dates fall in the age brackets reported from other regions of this plate boundary (mainly Sumatra) as well as distant shores of Sri Lanka, Thailand and mainland India. To understand the nature of distant deposits, we present observations from Kaveripattinam, an ancient port city on the east coast of India, where a high-energy sea surge deposit, found 1 km inland is attributed to a paleotsunami. The inland location of this archeological site at an elevation of 2 m and characteristics of the deposit that help discriminate it from typical storm deposition provide clinching evidence in favor of a 1000-year old regional tsunami (chapter 8). In chapter 9 we discuss the results of our study. We evaluate the nature of deformation/deposition and the calibrated age data in the context of their environments. Ages based on the organic material associated with coral debris (at Hut Bay and Interview Island) and the remains of mangrove roots, 1 m below the present ground level (at Port Blair) are considered as reliable estimates, due to their sheltered inland location and the in situ root horizon used for dating. Age data from Kaveripattinam is also considered reliable, based on its inland location beyond the reach of storm surges, sediment characteristics typical of tsunami deposition and ages based on multiple methods and samples. The age data based on the sites presented in this thesis are more conclusive about the 800 to 1100 AD and 1250 to 1450 AD tsunamis, and the former is represented from regions closer to the 2004 source as well as distant shores reached by its tsunami. Chapter 10 presents our conclusions and the scope for future studies. We present this as the first study of its kind in the northeastern Bay of Bengal, wherein the coseismic vertical coastal deformation features along an interplate subduction boundary and a variety of tsunami deposits are used to categorize depositional environments and ages of paleoearthquakes and tsunamis. To our knowledge, this is the first study of its kind where the effects of a recent tsunami have been used to evaluate paleodeposits based on their respective environments of occurrence. Our results have implications for tsunami geology studies in coastal regions prone to tsunami hazard.