Intraplate seismicity, oceanic basement topography and marine gravity
Louis Geli(1) , Jean-Yves Royer(2) , and Jean Goslin(2)
(2) CNRS-UBO, Place Nicolas Copernic, 29280, Plouzané, France
The intraplate seismicity that affects the ocean seafloor is poorly known, while it is of critical importance to study the thermal structure of the 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-magnitude earthquakes (typically 3<Ms<5) that are undetectable or imprecisely located by land-based seismological networks, providing unprecedented data and new insights on the low-level seismicity of the oceanic lithosphere, over areas extending over a few millions square kilometers.
However, to fully intrepret data from hydrophone arrays, it is necessary to recognize the tectonic environment near 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 least two reasons : 1) deep seafloor areas will not be covered by 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 thu remains the only way to map the structure of the rough igneous at a basin scale.
Here, we present some examples from the Pacific, Atlantic and Indian Oceans, showing the benefit that would be gained from improving the resolution of satellite derived models of marine gravity and bathymetry to optimize the use of hydrophone arrays and to study intraplate seismicity.