The geographic information in the assessment of geohazard in the marine environment

Slope instability and erosion, mass transport, volcanic and tectonic activity, fast sediment accumulation fluid escape are the main processes responsible for the geohazard in marine environment. A major knowledge about the geological setting of the offshore areas and related processes can be crucial to assess and manage the potential geological risks. High resolution morphobathymetric surveys, yielded in the frame of the MaGIC project (Marine Geohazards along the Italian Coasts), integrated with previously acquired data, single-channel seismic reflection profiles, backscatter data and sediments sampling, allow to define the geomorphological, stratigraphic and structural features in the offshore sector located in the north-western Sicilian continental margin and in the Ustica offshore (Southern Tyrrhenian). The main goals are: 1) to identify and map the main morphological-structural lineaments of the studied area; 2) to correlate the main structural lineaments on-and offshore; 3) to highlight the instability phenomena of the continental slope, being the area seismically active; 4) to draw up risk maps and to individuate the main dangerous sites; Morphostructural features recognized along the continental shelf to slope system highlighted erosional and depositional morphologies, structural elements at regional and local scale, submerged volcanic edifices, structures related to fluid escape as mud volcanoes and pockmarks. On the basis of the mapping of morphostructural elements and their integration with seismic data and sampling we identified the most likely elements of geological hazard. In the study area we individuated: 1) in the Gulf of Palermo, canyons making the continental slope very rough, also due to the occurrence of widespread mass wasting; 2) between the Gulf of Castellammare and the offshore of the Palermo Mountains, channels and erosional furrows, slumpings, turbiditic fans, landslides, pockmarks and tectonic lineaments; 3) in the offshore of Ustica island, volcanic structures, some of which aligned parallel to tectonic lineaments as Arso fault. The quantitative, GIS analysis allowed a better assessment of the real geohazard. Further investigation on the geological processes, ages of paroxysmal phenomena (eruption, landslides and earthquakes) are necessary to define the most appropriate monitoring strategies in order to assess possible risks for the coastal area and its infrastructures.