Twenty-five years of geodetic measurements along the Tadjoura-Asal rift system, Djibouti, East Africa

International audienceSince most of Tadjoura-Asal rift system sits on dry land in the Afar depression near the triple junction between the Arabia, Somalia, and Nubia plates, it is an ideal natural laboratory for studying rifting processes. We analyze these processes in light of a time series of geodetic measurements from 1978 through. A network of about 30 GPS sites covers the Republic of Djibouti. Additional points were also measured in Yemen and Ethiopia. Stations lying in the Danakil block have almost the same velocity as Arabian plate, indicating that opening near the southern tip of the Red Sea is almost totally accommodated in the Afar depression. Inside Djibouti, the Asal-Ghoubbet rift system accommodates 16 ± 1 mm/yr of opening perpendicular to the rift axis and exhibits a pronounced asymmetry with essentially null deformation on its southwestern side and significant deformation on its northeastern side. This rate, slightly higher than the large-scale Arabia-Somalia motion (13 ± 1 mm/yr), suggests transient variations associated with relaxation processes following the Asal-Ghoubbet seismovolcanic sequence of 1978. Inside the rift, the deformation pattern exhibits a clear two-dimensional pattern. Along the rift axis, the rate decreases to the northwest, suggesting propagation in the same direction. Perpendicular to the rift axis, the focus of the opening is clearly shifted to the northeast, relative to the topographic rift axis, in the ''Petit Rift,'' a rift-in-rift structure, containing most of the active faults and the seismicity. Vertical motions, measured by differential leveling, show the same asymmetric pattern with a bulge of the northeastern shoulder. Although the inner floor of the rift is subsiding with respect to the shoulders, all sites within the rift system show uplift at rates varying from 0 to 10 mm/yr with respect to a far-field reference outside the rift

Geoiede et dynamique interne de la Terre

SIGLEINIST T 70889 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Sismotectonique des failles actives en Indonésie, vue par Géodésie Spatiale

PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

The 1877 megathrust earthquake of North Chile two times smaller than thought? A review of ancient articles

International audienc

Quantification du couplage au long de la subduction chilienne

La subduction chilienne entre les plaques Nazca et Amérique du Sud est un laboratoire d'exception pour étudier l'accommodation de la convergence sur l'interface de subduction. La mesure par GPS de la déformation de la plaque supérieure pendant la phase intersismique permet de quantifier l'intensité du blocage via le coefficient de couplage cinématique. Il peut être déterminé en utilisant un modèle type "backslip". Ici, nous déterminons sa valeur sur la subduction chilienne (18-38S) et analysons ces variations en relation avec la segmentation sismotectonique. Les vitesses intersismiques collectées depuis 1990 ont été combinées et de nouvelles données GPS ont été acquises sur des réseaux installés ou rénovés depuis 2009. Cet effort instrumental et le travail de taitement des données conduit à un jeu de vitesses intersismiques sur plusieurs centaines de points. Ces données ont été utilisées pour élaborer une carte précise du couplage. La distribution de couplage montre des variations latérales et en profondeur et dessine une segmentation de la marge. Les segments fortement couplés semblent corrélés aux ruptures historiques et les intersegments découplés semblent se comporter comme des barrières. Le séisme de Maule du 27 février 2010 a permis de proposer un lien entre le couplage apparent et le comportement mécanique de l'interface. Il semble possible d'utiliser les cartes de couplage pour estimer l'aléa sismique au Chili. Nous apportons un éclairage nouveau sur la lacune du Grand Nord Chili. Les régions de l'atacama, du Paranal et du Loa correspondent à des zones fortement couplées et sont susceptibles de produire un grand séisme de subduction.The chilean subduction zone between the Nazca and South American plates is an ideal laboratory to understand the processes that take place on such a plate boundary. Measuring the elastic deformation of the upper plate during the interseismic phase using GPS can help assessing the degree of locking between both plates. We calculate the kinematic coupling using a simple backslip model. My aim was to obtain the coupling distribution along the entire chilean trench (18-38S) and to compare it to seismotectonic segmentation of the megathrust. I collected all the published interseismic velocities and combined them into a single data set. New data were collected and processed since 2009 on new or renovated campaign networks. We obtain a new date set on more than a hundred benchmarks. Those data were used to map precisely the coupling on the interface. It strongly varies both along strike and along dip and draws a segmentation of the megathrust. The highly coupled segments correlate well with historical megathrust earthquakes and intersegments, that are low coupled, correlate with zones that behave as barriers. The Maule earthquake that occured on February 27, 2010 ruptured a highly locked segment and stopped in low coupled intersegment areas. It gave us new insights on the relationship between apparent coupling and mechanical behavior of the subduction interface. Coupling maps should help estimating the seismic hazard along the Chilean subduction zone. In particular, we show here that the seismic hazard in the North Chile seismic gap may be lower than expected. Finally, Loa, Paranal and Atacama regions are zones that may rupture alone with a big subduction earthquake.PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Validation du comportement dynamique d'un système multi-agents : Application de l'éco-résolution à une cellule de production manufacturière

International audienceIn the reactive systems it could be difficult to plan tasks. Reactive multi agent system can solve this kind of problem. To skip planning work, multi agent system allows designers to distribute global system aim into local agent behaviour. Nevertheless it is difficult to get an actual idea of the global system behaviour. In this communication, we propose first a model of dynamic behaviour of an agent, and we shows how designers can deal with a tool of validation of discrete event system to validate a multi agent system. Un example in the filed of control of manufacturing cell of production will be used.Pour contrôler les systèmes fortement réactifs, il est difficile d'assurer une planification des tâches. Les systèmes multi-agents réactifs apportent une solution à cette classe de problème. En répartissant l'objectif général du système dans un ensemble de comportements individuels, le concepteur évite le recours à la planification. En revanche, il lui est difficile d'avoir une idée du comportement global du système. Dans cette communication, après avoir proposé un modèle de comportement d'un agent, nous montrons comment un concepteur peut tirer parti d'un outil de validation de comportement des systèmes dynamiques pour valider un système multi-agents. Un exemple concernant la commande d'une cellule de production manufacturière servira de support à notre exposé

GPS Statique, cinématique et haute fréquence appliqué à l'étude de déformations de zones sismiques

PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF