A study was carried out within Work Package 8 (WP8) of MARSITE in order to improve the characterization of the near-fault micro-seismicity within the Sea of Marmara. Velocity models were thus developed by KOERI and Ifremer respectively, following two different approaches: - KOERI developed a 3D velocity model for the whole Marmara Region (within latitudes 39.5°N - 42.5°N and longitudes 26.0°E - 30.5°E), including land and seabottom stations, with grid spacing of 9 km x 9 km x 3 km. - Ifremer developed an opposite, but complementary approach, strictly based on seabottom stations, for the Western Sea of Marmara (40°43’N - 40°54’N - 27°30’E - 28°15’E). A high resolution velocity model with a 750 m x 750 m x 400 m grid spacing was built, using multibeam bathymetry and wide-angle seismic data, in order to account for the velocity contrast at the water/sediment interface and the slow seismic velocities within the sediment infill in the main Marmara Trough. The velocity model developed by KOERI for the whole Marmara region by merging land and sea stations appears to be very useful to improve the quality of earthquake catalogs and the real time monitoring of the regional seismicity. In contrast, to improve the final-scale location of hypocenters near the submerged fault zone and enhance the search for seismic tremors, specific networks of permanent, cabled sea-bottom seismometers are required. Each network should be consistent per se, and allow the high-resolution characterization of earthquakes below the Sea of Marmara. In addition, it is of critical importance to create an high-resolution, 3D velocity model, in order to take into account for the velocity contrast at the water/sediment interface and the slow seismic velocities within the sediment infill in the main Marmara Trough.