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Observations D'interactions Sismiques Et D'une Phase De Nucléation De Grands Séismes

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Observations D'interactions Sismiques Et D'une Phase De Nucléation De Grands Séismes THÈSE Pour obtenir le grade de DOCTEUR DE L’UNIVERSITÉ DE GRENOBLE Spécialité : Sciences de la Terre, de l'Univers et de l'Environnement Arrêté ministériel : 7 août 2006 Présentée par Virginie DURAND Thèse dirigée par Michel BOUCHON et David MARSAN et co-dirigée par Jean SCHMITTBUHL préparée au sein de l'Institut des Sciences de la Terre dans l'École Doctorale Terre Univers Environnement Observations d'interactions sismiques et d'une phase de nucléation de grands séismes Thèse soutenue publiquement le 1er février 2013 devant le jury composé de : Raùl MADARIAGA Professeur à l'ENS, Paris, Président Hélène LYON-CAEN Directeur de Recherche CNRS ENS, Paris, Rapporteur Pascal BERNARD Physicien IPG, Paris, Rapporteur Marie-Paule BOUIN Chargée de Recherche CNRS IPG, Paris, Examinatrice Michel Campillo Professeur à ISTerre Université de Grenoble, Grenoble, Examinateur Michel BOUCHON Directeur de Recherche CNRS ISTerre, Grenoble, Directeur de thèse David MARSAN Professeur à ISTerre Université de Savoie, Chambéry, Directeur de thèse Jean SCHMITTBUHL Directeur de Recherche CNRS EOST, Strasbourg, Co-Directeur de thèse Université Joseph Fourier / Université Pierre Mendès France / Université Stendhal / Université de Savoie / Grenoble INP We have to understand not only faults but also how they interact with one another. We have to understand not only the earth's crust but also how the brittle crust interacts with the more plasticky layers below. We have to understand not only individual earthquakes, but also how earthquakes interact with other earthquakes. (Hough (2010)) R´esum´e Dans cette th`ese, nous pr´esentons trois ´etudes concernant les interactions entre s´eismes et la phase de nucl´eation des forts tremblements de terre. La premi`ere partie de ce travail concerne le NO de la Turquie, o`udeux syst`emes tectoniques sont pr´esents : d´ecrochement sur la Faille Nord Anatolienne et extension dans des essaims situ´esautour de la faille. Nous montrons que ces deux syst`emes interagissent, mais r´epondent diff´eremment `al'ex- citation du s´eisme d'Izmit (1999). Les calculs des changements de contraintes de Coulomb induits par le s´eisme d'Izmit indiquent que les ´ev`enements en d´ecrochement r´epondent aux contraintes dynamiques, alors que les s´eismes en extension semblent contr^ol´espar la d´eformation statique de la cro^ute. Dans la seconde partie de cette th`ese,nous analysons une importante s´equence sismique qui s'est produite en 2008 en Gr`ece. Cette analyse a montr´eque les s´eismes en subduction ou en d´ecrochement composant la s´equence re- fl`etent le mouvement du SO rigide de la Gr`ece vers le SSO accompagn´edu plongement de la plaque Africaine et du retrait vers le sud de la subduction. Cette premi`ere ´etape de d´eformation est suivie, quelques mois plus tard, de la d´eformation interne de la plaque Eg´ee qui se manifeste par de l'extension N-S. Cette s´equence sismique est le t´emoin de l'existence d'un couplage dynamique entre la subduction et le prolongement de la Faille Nord Anatolienne dans la r´egion ´eg´eenne. Enfin, le but de la derni`ere partie de cette th`ese a ´et´ed'apporter des ´el´ements de r´eponse `ala question : existe-t-il un ph´e- nom`ene observable par le biais de la sismicit´equi pr´ec`ede de mani`ere syst´ematique les grands tremblements de terre ? Pour cela nous avons ´etudi´el'activit´esismique pr´ec´e- dant des s´eismes de M 6:5 dans des r´egions bien instrument´ees (Japon, Cascades et ≥ NO des Etats-Unis). Nous montrons que la grande majorit´edes s´eismes interplaques est pr´ec´ed´eed'une acc´el´eration de la sismicit´e,au contraire des s´eismes intraplaques. Nous mettons ´egalement en ´evidence une diff´erence entre les s´eismes en d´ecrochement et les s´eismes en subduction : les pr´e-chocs des s´eismes en subduction sont localis´esdans une grande r´egion, rendant un d´eclenchement en cascade des ´ev`enements et du choc principal impossible. 3 Abstract We present three studies about earthquake interactions and the nucleation phase of big earthquakes. The first part of this work deals with the northwestern Turkey, where two tectonic regimes exist, with the transform North Anatolian Fault and extension clusters around it. We show that these two systems interact, but respond differently to Izmit earthquake (1999) stimulation. Computations of the Coulomb stress changes induced by the Izmit earthquake indicate that strike-slip events respond to dynamic stresses, whereas the extension ones seem to be controlled by the static deformation of the crust. In the second part, we analyze a seismic sequence that occurred in 2008 in Greece. This analysis shows that subduction or strike-slip earthquakes of the sequence depict the overall motion of the southwestern Greece to the SSW, accompanied by the plunge and the southward retreat of the slab. This first deformation stage is followed, few months later, by the internal deformation of the Aegean plate, which occurs as N- S extension. This seismic sequence depicts the existence of dynamic coupling between the Hellenic subduction and the prolongation of the North Anatolian Fault. The aim of the last part was to shed some lights on the question : is there a systematic seismic phenomena preceding the occurrence of big earthquakes ? To do that, we studied seismic activity preceding M 6.5 earthquakes in some well-instrumented areas of the North ≥ Pacific. We show that most of the interplate earthquakes are preceded by an increase of the activity, unlike the intraplate ones. We also highlight a different behavior between strike-slip and subduction events : foreshocks of subduction earthquakes are located in a large area, preventing a cascade triggering. 5 Remerciements Au cours de ma th`ese, j'ai rencontr´ede nombreuses personnes qui ont contribu´e`a rendre ces trois ans passionnants et inoubliables. Je tiens `ales remercier ici. Merci Michel Bouchon et David Marsan, mes directeurs de th`ese, pour avoir partag´e • avec moi votre passion pour la recherche, en me guidant sur cette longue route et en m'aidant `ad´egager les observations importantes du < bruit de fond >. Un grand merci pour les longues discussions scientifiques que nous avons eues, pour m'avoir permis de participer `ade nombreuses conf´erences, et pour la confiance que vous m'avez accord´eetout au long de ces trois ann´ees ! Merci aussi Michel de m'avoir rappel´emes motivations quand je les perdais de vue, notamment au moment de la r´edaction de ce manuscrit (< quelle est ta motivation, ´ecrire une th`ese, ou contribuer `adiminuer le risque li´eaux s´eismes ? > ... ces paroles m'ont quelque peu fait r´efl´echir !) Jean Schmittbuhl, pour avoir suivi de pr`esla progression de mon travail, et pour • tes commentaires constructifs. Hayrullah Karabulut, de l'Observatoire de Kandilli en Turquie, pour ton accueil • dans ton laboratoire. Merci Hyre de m'avoir montr´ela lourde t^ache que repr´esente la maintenance des stations sismologiques, qui sont `ala base de la sismologie, et de m'avoir fait d´ecouvrir la mer de Marmara, ses belles ^ıles et ses populations accueillantes ! aux membres de mon jury : • H´el`ene Lyon-Caen et Pascal Bernard, mes rapporteurs, pour leurs commentaires enrichissants sur mon manuscrit et pour les questions soulev´ees Raoul Madariaga, Marie-Paule Bouin et Michel Campillo pour la discussion tr`es int´eressante qui a suivi ma soutenance. J'ai eu la chance d'effectuer ma th`esedans un laboratoire dynamique et convivial. Un grand merci `atous les chercheurs, ´etudiants, personnels administratifs,... pour leur accueil chaleureux ! Je tiens particuli`erement `aremercier : Fran¸cois Renard pour m'avoir confi´el'organisation des s´eminaires de l'´equipe ! Cela • m'a permis de faire des supers rencontres. Merci aussi pour les nombreuses discus- sions sur l'apr`es-th`eseet pour les BDs qui m'ont aid´ees`ame changer les id´ees pendant la phase finale ! Anne-Marie, pour ta pr´esence (je savais pouvoir compter sur toi dans tous les cas !) • et pour m'avoir fait d´ecouvrir ton joli chalet en Vanoise ! l'ensemble de l'´equipe M´ecanique des Failles ! ! C'´etait un plaisir d'´evoluer au sein • de cette ´equipe ! Jean Virieux, notamment pour m'avoir confi´ele cours-TD de Fortran, que j'ai ador´e • pr´eparer, et pour tous tes bons conseils concernant la pr´eparation des cours, mais aussi la visibilit´ede mon travail de recherche ! Avant de passer aux ´etudiants, je veux remercier les secr´etaires, avec en premier lieu Ga¨elle et Zoubida, qui ont su garder le sourire en toutes circonstances, et sans lesquelles toutes les d´emarches administratives auraient ´et´ebien plus compliqu´ees ! Je remercie tous les ´etudiants du laboratoire pour tous les bons moments partag´es! Tous mes co-bureaux et compagnons de < table >, Tania, Jing, Guillaume, Tahir, Ju- lie, Nancy, Pascal, Mikael, Afifa, Hilal, Zahra, Anne, Amir, Johanes, Ismael, Isabella, C´ecile,..... Merci aussi `ames anciennes ´etudiantes Blandine, Julie et Audrey, pour les quelques soir´eesriches en fous rires ! Merci Tania, pour avoir support´emes sautes d'hu- meur et mes r^aleries en gardant toujours ton optimisme. Merci Julie, pour m'avoir sou- tenue pendant la phase finale. Un grand merci `aClara et Mikael, avec qui j'ai commenc´e `ad´ecouvrir les montagnes Grenobloises, merci Clara de m'avoir initi´eeau ski de fond ! Silvia, pour ta bonne humeur constante, et pour m'avoir donn´eton amiti´e(et avoir fait le long trajet Padoue-Grenoble pour assister `ama soutenance !).
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