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In the last decades gas hydrate occurrence along the Chilean continental margin has been well documented. In order to better define the seismic character of the hydrate-bearing sediments, we per-formed a detailed velocity analysis by using the pre-stack depth migration on part of multichannel reflection seismic line RC2901-734 located offshore Coyhaique. The velocity model shows a hydrate bearing layer above the BSR, with high velocity (1700e2200 ms#1) and maximumthickness of 250 mand a free gas bearing layer below the BSR, characterized by low velocity (1250e1400 ms#1). A weak reflector at about 70 m below the BSR marks the base of the second layer. By knowing the BSR depth, the seafloor depth, and the sea bottom temperature, the geothermal gradient was estimated. The resulting gradient varies from 35 to 95 !C km#1, with highest values at the structural high, and the lowest values located in the accretionary prism and in the fore arc basin. In order to quantify the amount of gas phase, the velocity model was converted into a gas-phase concentration model by using a theoretical approach. The results indicate that highest concentrations of gas hydrates, up to 23% of the total volume, are located in the fore-arc basin, and that highest concentration of free gas, up to 3% of the total volume, are located at the structural high, which may be considered as a natural trap for migrating fluids. Average concentrations are equal to 12% and 1% of total volume for gas hydrate and free gas, respectively.

The Earth's structure and the geod) nam ic processes that originate it are strictly interconnected: an accurate knowledge of the Earth·s structure and its physical properties is fundamental for the understanding of the dynamics of our planet and critical for realistic simulations of seismic ground motion. On the other side the separation and the definition of the different dynamic processes acting in a certain area help to better understand the structure and the physical properties of the investigated region. In recent years much emphasis has been given to the inversion or observed phase and waveform data for the best fitting set or model parameters at a variety of scale-lengths.

Results from several seismic methods allow us to sketch the deep structure of Etna and its Ionian margin. Under Etna a volume of high velocity material is found in a structurally high position; the emplacement of this suggests spreading of the surrounding medium. Just offshore, down-to-the-east normal faults penetrate through the upper crust. The deeper crustal structure beneath appears upwarped from the basin towards Etna. Juxtaposed with the crust of Sicily, a thinner crust reaches from the Ionian Basin under Etna, and the mantle is upwarped. In such a structure, magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth, rather than in an intracrustal chamber. This reduces the conflict between estimates of its volume from excess output of volatiles and short residence times. A link in time is indicated between volcanic and seismic activity at a large scale: over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 + earthquakes which caused destruction in southeastern Sicily. Several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of Catania and Augusta, which may be fault planes for such large earthquakes. They expand and prolongate the system of the Timpe faults on the eastern flank of Etna, thus linking large-scale tectonics offshore with the volcano. Etna developed together with normal faulting, upwarp, and spreading during the recent evolution of the former Ionian subduction. Activation of the material at depth at the lateral edge of the slab, by vertical motion with extension above, could produce the peculiar type of Etna magmatism.

The Straits of Messina and its surroundings are considered one of the most tectonically active areas of the Mediterranean; however, in spite of their hazard potential, modern geophysical data aimed at investigating the tectonic structures occurring in the marine areas are lacking. In order to bridge this gap, we carried out a multichannel seismic survey aimed at studying: i) the existence of the Taormina Fault, which many authors locate along the coast between Taormina and Messina; ii) the regional fault pattern in the area of the Messina 1908 earthquake; and iii) the instability offshore of Mt. Etna. Preliminary results show that the whole sector of the submarine slope located between Taormina and Messina has been tilted eastwards and that there is no Taormina Fault cutting the Quaternary sediments. On the other hand, the best-imaged active fault occurs on the Calabrian side of the Messina Straits. This NW-SE-trending fault is about 20 km long and dips westwards with a low-angle. Finally, a large submarine slide, longer than 10 km and thicker than 400 m, has been found offshore Mt. Etna.

A large seismic dataset has allowed us to regionally study the West Mediterranean Sea with particular focus on the West Sardinia and South Balearic continental margins and adjacent oceanic basins. The main seismic and geological evidences are related to the presence of the Messinian Trilogy in the deep basins and lower slopes, and coeval erosional truncation on the intermediate and upper margins. During the deposition of the upper Messinian sequence (UU), a thin salt layer has been highlighted, thanks to the high resolution of recent profiles. This salt layer, precipitated during the initial re-filling of the Mediterranean Sea, has been correlated to an erosional surface on the lower slope inner the UU and interpreted as the effect of a temporary sea level drop. The underlying salt layer (MU) shows halokinetic deformations in the deep basins which started since the Upper Messinian and developed principally during the Pliocene, sometimes until the Present, as testified by sea bottom piercings. The halokinetics has affected by different intensity, on the base of its original thickness, of the sediments and water load, and of the proximity of the lower slopes, where the sliding of salt toward the deep basin determined compressive stress and enhancing diapirism.

Sicily is a thick orogenic wedge formed by (1) the foreland (African) and its Sicilian orogen and (2) the thick-skinned, Calabrian–Peloritani wedge. The crust under central Sicily, from the Tyrrhenian margin to the coastline of the Sicily Channel, has been investigated by the multidisciplinary (SI.RI.PRO.) research project. The project dealt with the nature and thickness of the crust and depth and geometry of the Moho, which is essential in formulating subduction models and improving the knowledge of African and Tyrrhenian–European lithospheres. The results resolve features such as (1) the main orogenic wedge, (2) the very steep, NW–SE-trending regional monocline suggesting inflection of the foreland crust, (3) the deep Caltanissetta synform imaged, for the first time, to about 25 km, and (4) the top of the crystalline basement and the inferred crust–mantle boundary. The SI.RI.PRO. transect confirmed that the NNW-dipping, autochthonous Iblean platform of SE Sicily and its basement extends all the way into central Sicily. Further NW, towards the NNW end of the transect, a large uplift involves the Iblean platform and its underlying basement. The associated gravity anomaly is interpreted as the southern wedge edge of the Tyrrhenian mantle that splits the subducting Iblean–Pelagian (African) continental slab from an overlying synformal stack of allochthonous thrust sheets. Supplementary materials: Additional data are available at www.geolsoc.org.uk/SUP18594.

A crustal reflection seismic profile, more than 100 km long, was recorded across central Sicily, from the Tyrrhenian shore to the Sicily Channel, to understand the deep structures and the collision mechanisms between Europe and Africa and the subsequent geodynamic evolution. The profile was acquired using explosive sources and 240 active channels recorded by a Sercel 408-XL, 24 bits A/D converter, with a 12 km spread and a 24-fold coverage. The data were processed following a non-conventional procedure in order to preserve the relative amplitudes of the reflections and to better investigate the Sicily deep structures down to the Moho. The main highlighted structures are the dramatic flexure of the Iblean crust, the huge, deeper than expected, trough of Caltanissetta consisting of deep seated thrusts and nappes, and the imbricate thrust system of rigid bodies characterizing the northern Maghrebian chain. We designed an ad hoc acquisition and processing in order to highlight these main geological features in the seismic stacked section. Moreover, the deepest parts of the Caltanissetta trough are imaged for the first time, and its bottom is now fixed at more than 7 s TWT. The giant crustal wedge flexuring the Iblean foreland and the Moho geometries are examinated.