In-situ evidence for dextral active motion at the Arabia-India plate boundary

International audienceThe Arabia-India plate boundary--also called theOwen fracture zone--is perhaps the least-known boundary among large tectonic plates1-6. Although it was identified early on as an example of a transform fault converting the divergent motion along the Carlsberg Ridge to convergent motion in the Himalayas7, its structure and rate of motion remains poorly constrained. Here we present the first direct evidence for active dextral strike-slip motion along this fault, based on seafloor multibeam mapping of the Arabia-India-Somalia triple junction in the northwest Indian Ocean. There is evidence for 12km of apparent strike-slip motion along the mapped segment of the Owen fracture zone, which is terminated to the south by a 50-km-wide pull-apart basin bounded by active faults. By evaluating these new constraints within the context of geodetic models of global plate motions, we determine a robust angular velocity for the Arabian plate relative to the Indian plate that predicts 2-4mmyr−1 dextral motion along the Owen fracture zone. This transformfault was probably initiated around 8 million years ago in response to a regional reorganization of plate velocities and directions8-11, which induced a change in configuration of the triple junction. Infrequent earthquakes of magnitude 7 and greater may occur along the Arabia-India plate boundary, unless deformation is in the formof aseismic creep

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

Arabia-Somalia plate kinematics, evolution the Aden-Owen-Carlsberg triple junction, and opening of the Gulf of Aden

International audienceNew geophysical data collected at the Aden‐Owen‐Carlsberg (AOC) triple junction between the Arabia, India, and Somalia plates are combined with all available magnetic data across the Gulf of Aden to determine the detailed Arabia‐Somalia plate kinematics over the past 20 Myr. We reconstruct the history of opening of the Gulf of Aden, including the penetration of the Sheba Ridge into the African continent and the evolution of the triple junction since its formation. Magnetic data evidence three stages of ridge propagation from east to west. Seafloor spreading initiated ∼20 Myr ago along a 200 kmlong ridge portion located immediately west of the Owen fracture zone. A second 500 kmlong ridge portion developed westward up to the Alula‐Fartak transform fault before Chron 5D (17.5 Ma). Before Chron 5C (16.0 Ma), a third 700 km‐long ridge portion was emplaced between the Alula‐Fartak transform fault and the western end of the Gulf of Aden (45°E). Between 20 and 16 Ma, the Sheba Ridge propagated over a distance of 1400 km at an extremely fast average rate of 35 cm yr−1. The ridge propagation resulted from the Arabia‐Somalia rigid plate rotation about a stationary pole. Since Chron 5C (16.0 Ma), the spreading rate of the Sheba Ridge decreased first rapidly until 10 Ma and then more slowly. The evolution of the AOC triple junction is marked by a change of configuration around 10 Ma, with the formation of a new Arabia‐India plate boundary. Part of the Arabian plate was then transferred to the Indian plate