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The south Algero-Balearic basin is thought to be floored by middle Miocene oceanic crust (Panza et al., 2007) as young as 16 Ma originated at the buried spreading centre of the Hannibal Ridge (Mauffret et al., 2004). Accordingly, the oceanic basin opened in approximately E-W direction following the rift of the Kabylide thrust belt, triggered by the westward migration of the Gibraltar Arc. According to others (Rosenbaum and Lister, 2004), extension occurred approximately in a N-S direction similarly to the opening of the Provencal Basin, as a result of back-arc extension behind the eastward migration of the Maghrebian and Apenninic Arcs (see also Gueguen et al., 1998). Seismic facies of MSC unconformities and units are described. Furthermore, evidence of possible gypsum dehydration is discussed.

International audience; The Nile deep-sea fan is the largest Plio-Quaternary depocentre in the Mediterranean Sea, extending over an area of >150,000 km2 within which rapid deposition drives syn-sedimentary collapse tectonics, as well as widespread seafloor venting of mixed thermogenic and biogenic gases. It is thus an ideal setting for the near-seabed accumulation of gas hydrates, which are stable below water depths of about 1100 m in the warm waters of the eastern Mediterranean. Gas hydrates have yet to be sampled on the Nile fan, although their presence has been suggested from semi-published industry seismic and well log data. Here we integrate available industry data with a regional grid of academic geophysical data (seismic and multibeam) acquired by Géoazur, in order to identify a BSR on the central Nile fan, invert it to geothermal gradients, and examine its relationship to fluid venting. The BSR is observed on several intersecting seismic profiles of varying frequency content and offset, as a discontinuous reflection of negative polarity that lies 220-330 ms below seafloor, deepening downslope in water depths of 2000-2500 m. The BSR occurs within a relatively small area (2500 km2), among a larger system of slope-parallel extensional faults. Inversion of BSR depth to temperature gradients was performed using a velocity-depth function for deep-sea sediments, a phase boundary for methane hydrate in equilibrium with seawater of 3.86% salinity (Mediterranean average), and water temperatures from MEDATLAS. The results indicate spatially varying gradients of 27-42˚C/km, up to twice background values reported in the geothermally cool eastern Mediterranean offshore. ‘Shallow’ BSRs yielding elevated thermal gradients within the Nile fan can be explained in terms of advective heat transfer by upward fluid flux. Upward fluid migration is supported by evidence of widespread seafloor fluid venting, but seafloor data indicate few or no vents in the area of the BSR. In contrast, in an area with many gas vents over 50 km from the BSR, subsurface gas hydrate accumulations are indicated by resistivity log data at two well-sites. If gas and gas hydrates are present across wider areas, why is the BSR so restricted? We hypothesise that these observations can be explained in terms of spatially varying fluid flux, such that away from the BSR a greater flux of fluids rich in dissolved gas leads to rapid gas hydrate formation and the growth of gas chimneys. We intend to test this hypothesis during a forthcoming Franco-Brazilian campaign, focused on understanding the dynamics of the fluid vents. Acknowledgement : this work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 656821 (SEAGAS project).

Swath bathymetry and seismic reflection profiles collected by the Italian Antarctic Program (PNRA WEGA and MOGAM projects), combined with Australian (CSIRO) oceanographic measures (Williams et al., 2010) and benthic fauna sampling (Post et al., 2010), in the offshore of the George Vth Land, document evidence of bottom water cascading currents and turbidity currents inside continental slope canyons. The continental slope is incised by canyons heading to shelf edge sills and bounding sedimentary ridges of Miocene age. Dense shelf water forms in coastal polynya and is exported off the shelf break to form the Adélie Land branch of the Antarctic Bottom Water (ALBW, Rintoul et al., 2008). This bottom water is detected by CTD and mooring measurements up to about 3200m of depth, in the Jussieu canyon and further to the west. The speed of the ALBW is enough to transport fine sand and silt from shallow to deep water as documented by sea bed sediments. Similar bottom currents activity is recorded also during Quaternary glacial and interglacials (Caburlotto et al., 2009, Macrì et al., 2005) with source in the George V Land rocks and in the continental shelf (Damiani et al., 2006). The meandering charater of the Jussieu canyon and the sediment wave field on its eastern ridge, would suggest that they likely formed under the action of downslope, continous, bottom current, since the early Pliocene (Escutia et al., 2010). Caburlotto A., Lucchi R.G., De Santis L., Macrì P., Tolotti R. 2010. Sedimentary processes on the Wilkes Land continental rise reflect changes in glacial dynamic and bottom water flow. International Journal of Earth Sciences, 99(4), 909-926. Damiani D., Giorgetti G., Memmi Turbanti I. 2006. Clay mineral fluctuations and surface textural analysis of quartz grains in Pliocene–Quaternary marine sediments from Wilkes Land continental rise (East-Antarctica): Paleoenvironmental significance. Marine Geology, 226,81-295. Escutia C., Brinkhuis H., Klaus A. & Expedition 318 Scientists 2011. Proc. Intergrated Ocean Drilling Program, 318. Macrì P., Sagnotti L., Dinares-Turrel J., Caburlotto A. 2005. A composite record of Late Pleistocene relative geomagnetic paleointensity from the Wilkes Land Basin (Antarctica). Physics of the Earth and Planetary interiors, 151, 223-242. Post A.L., O’Brien P.E., Beaman R.J., Riddle M.J., De Santis L. 2010. Physical controls on deep water coral communities on the George v Land slope, East Antarctica 2010. Antarctic Science, 22 (4), 371-378. Rintoul S.R. 1998. On the origin and influence of Adelie Land bottom water. In: Ocean, Ice and Atmosphere: Interactions at the Antarctic Continental Margin. American Geophysical Union, Washington DC, 151-171.

In this work we present a comparison between two seismic datasets acquired by the oceanographyc research vessel OGS-Explora through the passive margins of the West Mediterranean sea: the West Sardinia continental margin of the Sardo-Provencal basin (WS10 dataset acquired in 2010) and the South Balearic continental margin of the Algerian basin (SF2012 dataset, acquired in 2012 within SALTFLU project). The West Sardinia margin was originated by the Oligocene-Early Miocene breakup of European plate followed by the drift of the Sardinian block and the southern French margin; the Algero-Balearic basin opened later respect the Balearic basin, dating its oldest oceanic crust 16My following the rift of the Kabylide thrust belt (Muffret et al., 2004 and cited literaure). Although the margins are different in age and geodynamic histories, here we intend to focus on differences and analogies concerning the geological features that characterize the Messinian and Post Messinian period, starting from the availability of already processed and interpreted seismic dataset of Western Sardinia (Geletti et al., 2014) and of processed by OGS and partly interpreted profiles of South Balearic margin. In particular this approach should allow us to correlate the Messinian and Plio-Quaternary units that deposited in the West Mediterranean. The comparison let to make considerations about the seismic facies of the Messinian sedimentary sequence that characterize the basinal domain and the slope of the North Algerian margin; analogies with the seismic facies of the Upper evaporite Unit recognized in the Sardo Provencal basin have been observed, represented by a thick well stratified package of high amplitude reflectors and intercalation of transparent layers. Observation about deformation structures mainly due to salt tectonic activity will be presented, basing on the already identification by Camerlenghi et al., (2009), of different kind of salt-induced abyssal plain sediment deformation. Basing on the fact that there are lack of information in this sector of Western Mediterranean due to the absence of calibrating boreholes, this work could be a starting point to a major comprehension of the distribution of the Messinian Salinity Crisis processes within the basins of the Mediterranean sea.

International audience; One of the objectives of the European project SEAHELLARC (SEismic and tsunami risk Assessment and mitigation scenarios in the western HELLenic ARC) was to identify the key elements controlling the geological structure of the Peloponnese continental margin in order to better understand the distribution of earthquakes in the area. Vintage multichannel seismic lines were reprocessed, interpreted and integrated with detailed morpho-bathymetric data and high-resolution single channel seismic data. According to the interpretation, most of the upper continental margin has been created within the former Alpine Gavrovo, Ionian and Apulian thrust units, including their Miocene to Quaternary cover and their Triassic salt-bearing formations. The Ionian thrust complex seems to have been continuously overthrusting the Apulian Ridge, itself characterised by strongly fractured acoustic basement features. Ductile and mobile Triassic evaporitic sequences are present in most of the major Ionian zone morpho-structures. The westward directed thrusts of the Ionian zone reached their final positions in Lower Pliocene and were followed by uplift of the ridges that is continuing in the present time. Previous compressional structures are being reactivated as normal faults with associated diapirism in the Triassic evaporites. NNE-SSW shear displacements related to trans-extensional motion may have activated "pull apart" basins with ENE-WSW normal faulting at their heads. This NNE-SSW dextral strikeslip motion agrees with the present anticlockwise rotation of the Peloponnese. The focal mechanism and the NNE-SSW distribution of aftershocks of a major earthquake in June 2008 along the Andravida fault define a major lineament that can be followed past the Katakolo Peninsula to the diapiric morpho-structures defining the eastern boundary of the Strophades basin.

International audience; Funded by the EEC Sixth Framework Program, the SEAHELLARC project was aimed to evaluate, and better understand the causes, of the various natural geohazards (chiefly earthquakes and tsunamis), which frequently affect the western Peloponnese area and particularly its coastal domain; this region is one of the most seismically active of Greece and therefore of the Mediterranean Sea. Based on a set of new geophysical data, such as detailed swath bathymetry and high-resolution sub-bottom Chirp, we have distinguished and studied four contrasted domains along this area of the Peloponnese active continental margin underlined by intense crustal seismicity and marked by very contrasted and often sharp continental slopes; from east to west these are: (1) an area including the continental shelf and the upper slope; there sedimentary overload and destabilizations, syn-sedimentary faults, mass transport deposits and active sedimentary by-pass mechanisms are the main risk factors. (2) The middle to lower continental slopes, is mainly expressed by two, N-S trending, fault-related, depressions, where active deformations, well recorded by actual tilting of the sedimentary blanket, occur. (3) West of this deep structural depressions exists a poorly sedimented ridge area (from which merges the small Strophades Islands) also showing N-S and E-W trending lineaments resulting in a dense network of fractures and scarps and leading too a particularly complex sub-marine morphology; this area, together with the westernmost deep domain (4), which bounds the continental margin, clearly records the effects of significant active tectonic. Our studies of the shallow and recent sedimentary cover of the continental margin off western Peloponnese, confirm that this active margin segment is an area where geohazards can be expected. In addition to fault ruptures, generated at depth by the specific tectonic framework, sedimentary collapses, particularly along the shelf break nearby Cape Katakolo, may trigger significant local tsunamis, which may in turn induce strong damages all along the nearby coasts up to the town of Pylos.

International audience

In order to define seismic hazard with sufficient accuracy required for engineering applications, we initiated a multidisciplinary geoscientific study offshore western Peloponnese, focusing on the Kyparissiakos Gulf. Multibeam swath bathymetry localised unstable coastal slopes, which were later investigated by high resolution seismic profiles. Sediments and crustal structures were studied by multi-channel seismic recordings and active large-offsets seismic profiling. We established an onshore/offshore local seismic array that recorded 3500 micro-earthquakes in two months, and combined the results with historical and digital seismicity data in order to understand the active crustal deformation. These findings were further combined with geological mapping and tectonic observations from onshore Peloponnese and available offshore data. All this geologic and tectonic information was coupled with evidence from the analysis of historical and recent seismicity with the aim of identifying the seismogenic sources. We have defined nine seismogenic zones in western Peloponnese that are significantly different from those published in the literature. The new zonation addresses more accurately the deformation of the crust and sediments, and is the basis for a reliable seismic hazard analysis and seismic risk assessment. We identified a large area of the northern Peloponnese and the lonian islands of Lefkas, Cephalonia, Zakynthos and Strophades, to be involved in a SW-ward oriented crustal extrusion, dominated by two major dextral deforming strike slip faults: Cephalonia and Andravida with their offshore prolongation. Some changes with respect to the Greek zonation in the literature have been introduced in the region surrounding the new nine seismogenic zones to reach a homogeneous cover of the whole Peloponnese. © 2014 - OGS.

The Jonian Clabrian inner margin is characterized by a very complex morphology, poorly known in details about its genesis and recent evolution, connected to intense morpho-tectonic dynamics of the Calabrian Arc. The study area covers approximately 6000 square km, including the continental shelf and slope between Capo Spartivento and Capo Rizzuto down to a depth of 1500 meters. Multibeam, CHIRP, grab, and cores samples are performed during two oceanographic cruises. The exploration aim has been the testing of some important processes of submarine erosion that affect also the coastal areas. The main results of this multidisciplinary researches are as follows : - the morphology of the margin is modelled in a very thick plio-quaternary sequence produced by the very high terrigenous supply from the Calabrian Arc; - various mass transport processes towards the outer margin are active and both diffused along the slope (creeps, slides, slumps) and focussed inside the main canyon systems (turbidity currents, mud flows); - the generally narrow continental shelf shows remarkable width variations; where the canyon heads are well developed, the shelf is absent. All these features suggest a recent acceleration of the erosive processes. In the main canyon systems, the head retrogressive erosion affects the continental shelf until it interacts with the coastal morpho-sedimentary processes. In many cases the relationship between the morphological features and the main structural lineaments of the Margin is well evident. Its recent activity is testified by the high seismicity of the area. The widespread slope instability, the active mass wasting processes and the historical seismicity suggest that the whole area represents a case study for longterm tsunami hazard researches and risk evaluation.

The CROP-11 deep seismic profile across the central Apennines, Italy, reveals a previously unknown, mid-crustal antiform here interpreted as a fault-bend fold-like structure. The seismic facies and gravity signature suggest that this structure consists of low-grade metamorphic rocks. Geomorphological, stratigraphic and tectonic evidence in the overlying shallow thrusts suggests that this structure developed in early to mid- Messinian time and grew out of sequence in late Messinian– Pliocene time. The out-of-sequence growth may reflect a taper subcriticality stage of the Apenninic thrust wedge, which induced renewed contraction in the rear.