INTRAPLATE SEISMICITY, OCEANIC BASEMENT TOPOGRAPHY AND MARINE GRAVITY

摘要

The intraplate seismicity that affects the ocean seafloor is poorly known, while it is of critical importance to underst understand the thermal structure of the and oceanic lithosphere and assess the pecularities - if any - of the earthquake generation processes in submarine environments. T-waves generated by submarine earthquakes can propagate almost without attenuation in the SOFAR (Sound Fixing And Ranging) channel, as far as a few thousands kilometers away from the epicenter. Hydrophones arrays have thus been recently used to detect small small-magnitude earthquakes (Ms<3) that are undetectable or imprecisely located by lan land-based seismological networks, providing unprecedented data and new insights on the low low-level seismicity of the oceanic lithosphere, over areas extending over a few millions square kilometers. However, to fully intrepret hydrophone arrays, it is ne necessary to recognize the tectonic environment near cessary the epicenter, using structural maps of the seafloor. Marine gravity and bathymetry derived from satellite altimetry are, to date, the only means to improve this knowledge at a global scale, especially in the remotest areas of the world's oceans,for at n least two reasons : 1) deep seafloor areas will not be exhaustively surveyed with shipboard multibeam systems in a foreseeable future ; 2) some areas, such as for instance,the Central Indian Ocean Basin, where a very active intraplate seismicity occurs, are thickly covered with sediments. Marine gravity thus remains the only way to map the structure of the rough igneous at a basin scale. Here, we present some examples showing the benefit that would be gained by improving the resolution of satellite derived models of marine gravity and bathymetry in deriving a detailed basement topography grid. Such a grid would in turn represent a most valuable framework to study intraplate seismicity from the I interpretation of nterpretation hydrophone acoustic data. These examples concern the study of : ? intraplate seismicity within the Indian Ocean through the IONETH Project ? intraplate seismicity within the North Atlantic Ocean ? seismic precursors prior to large earthquakes at oceanic fracture zones ? the rheology of the oceanic lithosphere.