The GROSMARIN cruise deployed 21 ocean bottom seismometers (OBS) on the North-Ligurian margin and the northern part of the basin. This was followed by seismic shooting with a powerful refraction source. The shots were recorded by the deployed OBS and by an array of stations on shore. The entire array was left on the seafloor, to be retrieved on 2 later legs in June and October 2008 aboard the DT/INSU inshore vessel « Tethys II ». Until then, it will record the seismicity of the area in the immediate vicinity of the structures, whose activity has generally been poorly defined or even undetected by permanent onshore seismological arrays. The related project is Actions Marges. This cruise aimed to: (1) investigate the North-Ligurian margin structure at crust level and its variability across and along the margin using 3D tomography created from shot signals; (2) characterize the seismically active zones by precisely locating the small-scale seismicity using the seafloor array. This is done to better characterize active faults and the resulting seismic hazards on the Ligurian cast between France and Italy. The cruise falls under the Géosciences-Azur BALIZ programme.