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The processes associated with magma injection at shallow depths within the crust have been the topic of many geophysical studies, some investigating the seismicity that accompanies volcanic activity and others attempting to map the subsurface extent and geometry of the resulting magma bodies. The aim of this study is to obtain a better understanding of these processes by investigating the nature of seismic signals that accompany volcanic eruptions and by seismically imaging a magma body beneath a mid-ocean ridge, both located on, or adjacent to Iceland. The seismic phenomena associated with the 1996 Vatnajӧkull subglacial eruption in central Iceland, have been studied using data recorded by both temporary (HOTSPOT) and permanent (SIL) seismic networks. These networks comprise 60 broadband and short-period three-component seismographs and cover most parts of the country. Two very active volcanic systems, Bárdarbunga and Grimsvӧtn, are situated underneath the Vatnajokull ice cap. The volcanoseismic signals recorded there were categorised according to their waveform shape and frequency content, into three groups: (a) low-frequency events (1-2 Hz); (b) mixed-frequency events (1-4 Hz); and (c) volcanic tremor. The eruption was preceded by intense seismic activity which began with a = 5.6 earthquake located at the Bárdarbunga volcanic system. The epicentres of the earthquake swarm that followed the M(_w), = 5.6 event initially delineated the Bárdarbunga caldera rim and then migrated towards Grimsvӧtn, to a place where a fissure was later observed. Pre-eruptive tremor started at least two days before the eruption as a harmonic signal around five narrow frequency bands (0.5-0.7, 1.6, 2.2, 2.8 and 3.2 Hz). Co-eruptive tremor started as a broadband, continuous signal which evolved into low-amplitude background tremor interrupted by high-amplitude, cigar-shaped bursts. Further analysis revealed that continuous tremor and the cigar-shaped bursts had all the characteristics of low- dimensional chaotic signals. Geophysical and geochemical evidence suggest that a lateral migration of magma from Bárdarbunga facilitated the rupture of the roof of a magma chamber, situated at the fissure area, which subsequently erupted as tephra on the glacier. The second phase of the RAMESSES (Reykjanes Ridge Axial Melt Experiment: Structural Synthesis from Electromagnetic and Seismics) experiment involved the acquisition of multichannel seismic reflection data from 39 along- and across-axis lines shot over the magmatically active 57º 45'N axial volcanic ridge. The data from one along-axis line were processed using a variety of techniques that mainly aimed at reducing the large amount of coherent noise present, a result of scattered energy at the rough seabed. The final processed section revealed a number of reflection events that could be interpreted as intra-crustal reflections, originating from the interface between pillow lavas and sheeted dykes, and from the top part of a thin melt lens.

Depuis maintenant une dizaine d'années, la vision du cycle sismique en zone de subduction a beaucoup évolué. Des découvertes récentes ont mis en évidence une grande diversité des régimes de glissement dans ces zones, avec notamment des glissements asismiques transitoires appelés « séismes lents » (SSE) et des vibrations de faibles amplitudes, persistantes dans le temps, appelées « trémors non volcaniques » (NVT). Ce travail a pour objectif l'étude des trémors non volcaniques afin de caractériser ces nouvelles manifestations des zones de faille. Nous avons abordé ce problème avec deux approches distinctes :1. Observer les trémors dans le milieu naturel afin de déterminer leurs caractéristiques. La zone étudiée correspond à la lacune sismique de Guerrero le long de la subduction mexicaine. Nous avons développé une méthode de détection et de localisation des NVT au Mexique grâce à des analyses d'antennes par formation de voie sur les corrélations. Cette méthode permet de mettre en évidence cer taines caractéristiques des NVT : une complexité des sources pour un épisode de trémors, une corrélation entre les activités de NVT et les pics de vitesse des glissements lents à plus long terme. Par ailleurs, l'étude de l'impact du séisme de Maule (2010, Chili, Mw 8.8) au Mexique montre qu'il a déclenché le second sous évènement du séisme lent de 2009-2010. Ce déclenchement d'un SSE s'ac- compagne de fortes activités de trémors, modulées par les ondes du séisme de Maule dans un premier temps, puis simplement associées au SSE.2. Modéliser les trémors expérimentalement et numériquement pour mieux com- prendre leur origine physique et leurs évolutions sur le long terme. Nous avons en particulier utilisé une expérience de frottement à faible vitesse qui indique une corrélation systématique entre les accélérations d'un glissement et l'émission de signaux qui ressemblent à des NVT. Une modélisation numérique de la zone de subduction mexicaine est également présentée et montre la possibilité de reproduire des trémors en considérant une transition d'affaiblissement critique associée à un processus de décrochage. / The vision of the seismic cycle in subduction zones has considerably evolved over the last 10 years. New discoveries has pointed the diversity of slip behaviors in these zones with aseismic slow slip called « slow slip events » (SSE) and persistent low amplitudes vibrations called « non-volcanic tremors » (NVT). The goal of this thesis is to study the non-volcanic tremors in order to characterize these new manifestations of fault zones. We used two different approaches: 1. We first observed the non-volcanic tremors in the nature in order to characterize this phenomenon. The area of interest is the Guerrero seismic gap along the Mexican subduction zone. We develop a new detection and location method based on beamforming of correlations of seismic signals. This new method exhibits some characteristics of NVT: a complex source for a single tremor episode and a correlation between the NVT episodes and the long-term peak of movement velocity in southwards direction. Moreover, the study of the consequences of the Maule earthquake on the Mexican subduction zone showed that this earthquake triggered the 2009-2010 SSE in Guerrero. This triggering of slow slip is accompanied by strong seismic tremor actvity that are first modulated by the passing waves and then associated to the SSE. 2. We model numerically and experimentally the tremors in order to better understand their physical origin and their long-term evolution. We used a very slow friction experiment that indicates a systematic correlation between slip acceleration of a slider and emission of acoustic signals that are similar to NVT. A numerical modeling of the Mexican subduction zone is also presented and shows the possibility to reproduce NVT with a critical depinning transition.

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Mémoire en neurologie vétérinaire / Plusieurs bouledogues anglais (BA) présentaient des tremblements de tête. Les 3 objectifs de ce projet étaient de déterminer la prévalence du syndrome de tremblements épisodiques de la tête (STET) chez les BA du Québec, caractériser la sémiologie du syndrome et déterminer s’il y a une cause sous-jacente. L’étude de prévalence a été complétée en contactant tous les propriétaires de BA présentés au Centre Hospitalier Universitaire vétérinaire entre 2005 et 2012. Vingt-deux des 116 répondants ont confirmé la présence d’épisodes de STET, affirmant une prévalence de 19% (CI 95% 12.3-27.3%) de STET chez les BA québécois. Le mâle est prédisposé au STET (p=0.017). Une étude rétrospective par questionnaire effectuée en ligne auprès des propriétaires de BA atteints a ensuite été complétée. Les 71 questionnaires retenus ont été analysés au moyen de statistiques descriptives. Le STET est caractérisé par un tremblement rapide de la tête débutant à 1.7 an d’âge (médiane), d’une durée de moins de trente minutes, de fréquence variable, occasionnellement déclenché par un stress et qui peut parfois être interrompu. Les tremblements causent de l’anxiété, mais sont autrement bénins et disparaissent spontanément dans 40% des cas. L’investigation diagnostique détaillée incluant des examens neurologique, sanguins, urinaires, de fonctions endocriniennes, d’imagerie par résonance magnétique du cerveau, d’électroencéphalographie, d’électromyographie et d’analyse du liquide céphalorachidien chez 5 BA atteints n’a pas révélé d’anomalie métabolique ou anatomique significative. En conclusion, le STET est une condition fréquente, mais bénigne chez le BA, dont la physiopathologie demeure indéterminée. Il est nécessaire de reconnaitre ce syndrome afin d’éviter des traitements inutiles et potentiellement néfastes. / Many English bulldogs (EB) were presenting head tremors. The 3 objectives of this study were to determine the prevalence of Episodic Head Tremor Syndrome (EHTS) in Quebec’s EB, to characterize the semiology of the syndrome and to determine if there is an underlying cause to this syndrome. The prevalence study was completed by contacting all the owners of EB presented to the Centre Hospitalier Universitaire Vétérinaire between 2005 and 2012. Twenty-two of 116 owners confirmed the presence of EHTS episodes, resulting in a prevalence of 19% (CI 95% 12.3-27.3%) of EHTS in Quebec’s EB. A male sex predisposition was identified (p=0.017). The retrospective study was conducted using an online detailed survey submitted to affected EB’s owners that voluntarily enrolled in the study. The 71 retained surveys were analyzed using descriptive statistics. EHTS is characterized by rapid head tremors that start at approximately 1.7 years of age (median), are less than 30 minutes in duration, of variable frequency, occasionally triggered by stress, and can sometimes be interrupted. The tremors cause anxiety but are otherwise benign and have a spontaneous resolution rate of 40%. Amongst the 5 affected EB that underwent diagnostic testing (neurological examination, bloodwork, urinalysis, endocrine function testing, brain magnetic resonance imaging, electroencephalography, electromyography and cerebrospinal fluid analysis), no underlying anatomical or metabolic abnormality was identified. In conclusion, EHTS is a common but benign condition in EB. The pathophysiology is still undetermined. This syndrome needs recognition to avoid useless and potentially harmful treatment.

<p dir="ltr">Parkinson’s Disease (PD) is the second most common neurodegenerative disorder with tremor being its primary motor symptom. Although the MS-UPDRS is the current clinical method for evaluating the severity of tremors in PD, it has several drawbacks resulting from the subjective, visual-based examination, and the ordinal scale used to rate the tremors. Since, the MS-UPDRS is agnostic to the etiology of the tremor, age related increase in naturally occurring physiological tremors may confound the precise rating of PD tremors. However, replacing the judgment of the neurologist in determining the holistic progression of PD and treatment protocol is neither feasible nor advisable. This research used lightweight, wearable, non-invasive sensors to detect, analyze, and differentiate changes in wrist kinematics due to physiological and PD tremors. Findings reveal key differences and similarities in composition between these different types of tremors. Dominant frequency analysis using a data-based approach shows interesting parallels with the frequency range found in literature for these tremors. Finally, using features of tremor signal obtained from the sensors, a novel Tremor Severity Score rating scale was created that shows greater sensitivity in differentiating rest and postural tremors as well as medication effects on these tremors in PD patients compared to the MS-UPDRS. This study offers a simple method for objectively evaluating Parkinsonian tremors, identifying kinematic distinctions between rest and postural tremors, analyzing the effect of anti-parkinsonian medication on these tremors, and sensitively scoring tremors. These objective methods could be valuable for early diagnosis and distinguishing between different tremor causes in both clinical and telehealth settings, as well as for investigating the effects of various treatment methods on tremors.</p>