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The southern Sicily coasts represent an important contribution to Italian tourism and marine geological processes in the Sicily Channel could pose a significant risk to neighbouring populations and goods. In this work, we are presenting the first results of the data collection that allowed us to identify and map several geological elements that can be used to assess submarine geohazards in the Sicily Channel. By using multibeam data and high-resolution seismic reflection profiles acquired during the ACUSCAL 2015 Cruise, we defined the characteristics of the morphostructural highs, and the morphology of slope failures and the stratigraphy of the mass transport deposits (MTD). In particular, we studied in detail the Graham Bank, which is located in a shallow sector of the north-western Sicily Channel at a distance of 45 km from the Sicilian coastline, where seven seamounts (M1-M7) have been identified and studied in detail within a small area, between 10 and 350 m deep. Their morphometric parameters allowed classification to be implemented on a shape basis. The volcanoes are 115-180 m high and 500-1500 m wide. M2 and M3 (3.5 km X 2.8 km) form the Graham Bank. Most of them show strongly inclined flanks with an average slope of 30°. Most of these seamounts are aligned along two trends (NW-SE and N-S), parallel to the main tectonic structures of the Sicily Channel. The identified structures show physical characteristics, which are very similar to several submarine volcanoes described elsewhere on the seafloor, allowing to conclude that they are volcanic seamounts. In this regard, it is important to highlight that the Graham Bank was affected in the last 100 years, by many eruptions (Colantoni et al. 1975). Furthermore, we distinguished slope failures relating to different mechanisms. In the western flanks of the M2 and M3, volcanic activity and concurrent up-slope triggered mass failures. In the eastern flank M2 gravitational collapse of volcanic edifices is mainly linked to neotectonic activity and volcanism. In the central part of the study area, a MTD is linked to neotectonic activity and to the rise up of volcanic rocks. These MTDs were mapped and described as potential tsunamigenic elements and their volumes were estimated. This work allowed us to understand geological features and processes in a tectonic-volcanic environment, which may represent a threat for coastal areas of the southern Sicily.

The geological, geomorphological and sedimentological features of the north-western Sicily continental shelf are here illustrated with the aim to propose a geological model able to explain the Neogene-Quaternary evolution of the Sicilian continental margin in the context of the central Mediterranean region. Above the continental shelf and upper slope the sedimentary succession, showing along the different sectors of the margin considerably variable internal geometry and stratigraphic relationships with the underlying units, is interpreted as a IV order depositional sequence (Late Quaternary Depositional Sequence, LQDS) deposited during the last eustatic change (last 125 ky). The lower boundary of the LQDS is represented by a subaerial erosional surface formed during the last eustatic sea level fall ended in the LGM (20-18 ka). This unconformity lies above a seaward dipping Pleistocene succession whose depositional architecture is in turn controlled by Quaternary eustatic sea-level fluctuations. A dense dataset of morphobathymetric and high resolution seismic data allowed to recognize along the continental shelf to bathyal plain system different types of continental shelf with different stratigraphic and morphostructural settings, associated to both large-scale processes and specific factors related to more local control: a) predominantly rocky shelves, both accompanied by a moderate frontal sedimentary prism and with a structural edge, in the structural highs of the Monti di Palermo offshore and around the main rocky headlands (Capo San Vito, Monte Catalfano); b), depositional shelves, in the Castellammare, Palermo and Termini Imerese gulfs, both with a regular seaward deepening of the substrate and with a substrate uplift at the shelf break. We confirm that depositional sequences in this margin are the result of the interaction between sea level changes and sedimentation, but demonstrate that the tectonic activity has played a key role, not only in the creation of different types of continental shelves, but also to determine the different characters of each sequence in different areas. The general tectonic uplift during the Pleistocene, together with the episodic alternation of extensional and compressional events, often with strike-slip component, is responsible for the thickness and facies variation both onland, where residual Pleistocene marine deposits today outcrops, and in the continental shelf, where most of the depositional sequences developed and are now recognized. As well tectonic activity exerted a control on the geomorphological features (e.g. pockmarks and mounds) of the present day coastal areas and shelf-slope system, as well as for the submarine canyons and the mass failure processes.

The Map Sheet 1:50.000 595 ”Palermo” includes marine and land areas of the topographic map sheet “Palermo”. The map sheet “Palermo” (Palermo Province) covers a part of the Sicily Fold and Thrust Belt (FTB) which has developed along the plate boundary between Africa and Europe in the Central Mediterranean. The Sicily FTB links the African Maghrebide to the Calabrian arc and Southern Apennines. The FTB and its submerged western and northern extensions are part- ly located between the Sardinia block and the Pelagian-Ionian sector, and partly beneath the central southern Tyrrhenian Sea. In this sector of the Mediterranean area, the main compressional move- ments, after the Paleogene Alpine orogeny, began with the latest Oligocene-Early Miocene counterclockwise rotation of Corsica-Sardinia, believed to represent a volcanic arc, and its collision with the African continental margin. Thrusting oc- curred in connection with the westward subduction of the Adriatic and Ionian lithosphere beneath the Corsica-Sardinia block. Today, a westward subduction is indicated by a North-dipping Benioff zone, as deep as 400 km, west of Calabria and the Apennines, and the related calc- alkaline volcanism in the Eolian Islands. Subduction and thrusting are contempo- raneous with a back arc-type extension in the Tyrrhenian Sea.186 LAND AREAS geomorphoLogy Three different sectors can be distinguished in Sheet 595: 1) the Palermo and Bagheria coastal plains, characterized by several poly- cyclic marine terraces organized in different orders; 2) the isolated carbonate reliefs of Monte Pellegrino and Monte Catalfano; 3) the internal Belmonte Mezzagno highlands and the Oreto and Eleuterio river valleys. The geomorphological evolution of the area has been controlled by strong down-cutting and dismantling processes that have produced both the erosion of thick volumes of mainly Tertiary terrigenous deposits and the exhumation of mainly Mesozoic carbonate rocks. Due to tectonic uplifting, these proces- ses are intensely developed on ”soft rocks “(Numidian Flysch clayey deposits), producing large river valleys with slopes affected by water erosion and surficial landslides (valleys of Fiume Oreto, Fiume Eleuterio and Fiume Milicia); they have, however, considerably slowed down along the blocks of more resistant rock (Mesozoic-Tertiary carbonate units), forming the wide Palermo Mountains. At the present-day, relict (planation surfaces and abandoned valleys), structural (fault/fault-line scarps) and karst (sinkholes and polje) forms occur in the highlan- ds. The geomorphological setting of the coastal areas has been influenced more by significant Quaternary extensional tectonics that originated the drowning of the northern sectors of the Sicilian chain in the Tyrrhenian Sea above which the marine deposition was deposited (Marsala synthem). The uplifting, involving also the lowered blocks, has resulted in the progressive retreat of the sea that gave origin to a succession of marine terraces, Ionian-Latest Pleistocene in age, and fi- nally the emersion of the present-day coastal depressions (Palermo and Bagheria plains). During the Upper Pleistocene to Holocene, the uplifting rates reached values generally lower than 0.1 m/ky. stratIgraphy The carbonate and terrigenous rock facies analysis and stratigraphy led to the recognition of large Paleozoic to Miocene sedimentary bodies pertaining to diffe- rent and separate crustal paleogeographic domains; the former, developed along the African passive continental margin and the adjacent Tethyan ocean. The “Tethyan” successions correspond to the deep clayey carbonate and vol- canoclastic rocks known to have been deposited in the Sicilide Domain. The pas- sive margin rock bodies are shallow water carbonates, deep water carbonates and 187 siliceous carbonates that were deposited in domains, locally known as Panormide, Trapanese and, Imerese. Terrigenous, evaporitic and clastic-carbonate rocks, Miocene to Pleistocene in age, formed during the foredeep evolution of the Sicilian FTB. A detailed stratigraphy of the rock-successions is summarized in the paragraph “Legend of the Palermo Sheet”. Quaternary continental deposits have been mapped as unconformity-bounded stratigraphic units limited by lower and upper unconformities, locally marked by palaeosoils, due to erosion/depositional processes, marine/sub-aerial processes or non-depositional events. Locally, the upper boundaries are the present-day topo- graphic surface. The detection of some unconformities of regional extent allowed us to define several synthems. The Marsala synthem is a Lower Pleistocene body of marine/coastal deposits, with abundant fossils; its lower boundary is a mari- ne erosion surface cutting pre-Quaternary rocks. The Buonfornello-Campofelice synthem is composed of middle Pleistocene marine deposits covering abrasion surfaces above the coastal stepped blocks. The Polisano synthem is made up of aeolian sandstones and sands with intercalations of breccias talus, late Middle Pleistocene in age (OIS 6); its lower boundary is a non-depositional surface at the top of older rocks. Eleuterio and Milicia synthems are made up of Middle-Upper Pleistocene, mainly fluvial, deposits deposited on river terrace surfaces; their lo- wer boundary is a stream erosion surface. The Benincasa synthem includes colluvial Middle-Upper Pleistocene deposits of Qz-sandstones interbedded with stone-line, palaeosoils, Fe-rich layers and no- dular concretions. Its lower boundary is an unconformity above the Buonfornello- Campofelice synthem, the upper one is the base of the Capo Plaia synthem of the present soil. The Barcarello synthem encompasses marine/coastal conglomerates and are- nites, with a rich warm-temperate “Senegal fauna” including Strombus bubonius; it is located on two orders of marine terraces (OISs 5e and 5c or 5a) and laterally passes into welded colluvial deposits whose age is correlated with the OIS 5. The lower boundary of the synthem is a marine abrasion surface, laterally extending to a continental erosion surface; the latter is cutting the Polisano synthem or older rocks. The Raffo Rosso synthem consists of aeolian sandstones and sands, collu- vial or gravitational deposits and thick stratified slope deposits of the last glacial climatic event (OISs 4-2); the lower boundary is a non-depositional surface at the top of the Barcarello synthem or older rocks. The Capo Plaia synthem is made up of coastal to continental deposits of the last glacial climatic event of the end - Holocene age (OISs 2-1); its lower boundary is formed by variously origina- ted erosion or non-depositional surfaces; the upper boundary is the topographic surface.188 struCturaL graIn The Paleozoic to Cenozoic, mainly carbonate sedimentary bodies, developed in different sectors of the African passive continental margin and the adjacent Tethyan ocean and were progressively accreted in a pile of tectonic units and are now exposed to form the Sicilian fold and thrust belt. To define the extension and setting of these bodies versus their internal facies pattern, we individuate them as Structural-Stratigraphic Units (U.S.S.), described as large geological bodies per- taining to original paleogeographic domains from where they were removed and later deformed. These bodies are bounded by clearly mappable tectonic features (faults, thrust, etc.) and each of them is characterized by homogeneous lithologies and similar structural behaviours and settings. The outcropping tectonic edifice, in the “Palermo” Sheet, is composed of se- veral U.S.S., which can be locally subdivided into tectonic units of minor order. These subunits have been mapped on the basis of their tectonic relationships. Some U.S.S. have been identified, starting from the geometrically highest and most internal in the FTB. 1) U.S.S. deriving from the deformation of the Sicilide domain succession: - U.S.S. Tusa-Troina outcropping in the south-eastern sector, overlying the Numidian Flysch deposits. 2) U.S.S. deriving from the deformation of the Imerese domain succession and its overlying numidian flysch basin. The units widely outcrop in the cen- tral and southern sector of the geological sheet where Mesozoic deep water carbonates and their oligo-miocene numidian flysch covers are deformed, with the latter often slightly detached from the carbonate substrate. Among them we distinguished: - U.S.S. Sagana - Belmonte Mezzagno, in the western sector, where we indi- viduated the sub-unit Pizzuta-S.Cristina; - U.S.S. Monte Cane-San Calogero, in the eastern sector, subdivided into a) the subunit Monte Cane-S. Onofrio, overlying b) the subunit Bizolelli; 3) U.S.S. deriving from the deformation of the Panormide Domain. The U.S.S. consists of Meso-Cenozoic shelf to pelagic carbonates and the often detached nu- midian flysch cover, pertaining to the U.S.S. M. Gallo-M. Palmeto, forming the margin of the Panormide Platform. It outcrops only at Monte Pellegrino (subunit Pellegrino). 4) U.S.S. deriving from the deformation of the Trapanese domain. It is recognizable only in the seismic profile crossing the eastern sector where it is overlain by the U.S.S. Sagana - Belmonte Mezzagno. Southwards, it oucrops at Monte Balatelle (U.S.S. Kumeta-Balatelle).189 Structural evolution The tectonic edifice outcropping and buried beneath the area of the Palermo Sheet is the result of several deformational events that have taken place since the Triassic, deforming complexly the sedimentary successions deposited during the Mesozoic-Pleistocene. After the detachment from their crystalline basement the original sedimentary bodies were progressively accreted in a pile of tectonic units now exposed in the Sicilian chain. Two main events have occurred during the Miocene and Pleistocene time interval. They are respectively characterized by compression and transpression. Contraction originally involved the Tethyan domains and the internal domains of the continental margin, whose deep water meso-cenozoic carbonates formed the structurally highest tectonic units in the chain. The occurrence of intrastratal decollement originated duplex geometries. Since the Messinian, the deformation moved at depth, progressively involving the carbonate platform rock bodies in large E-W antiforms that were successively (during Late Pliocene) folded by NE- SW structures. The transpressional event is proved by NNW-SSE and NE-SW transcurrent and transpressive structures (dextral); it involves the deep-seated car- bonate platform-forming fold structures and severe uplifting that induces reimbri- cation in the overlying Imerese deep-water units. This transpressive event accom- panies the paleomagnetically evidenced thrust rotations between the Late Miocene and the Early Pleistocene. An abrupt change in the tectonic transport direction of the two compressional structure systems is explained taking into account the 120° clockwise rotations based on the paleomagnetic results of ChanneL et alii (1980, 1990); speranza et alii (2000). As a consequence the present day outcropping structural attitude of the structures (and consequently of the deformation fields) do not coincide with the original trends. The compressional and traspressional structures are down faulted northwards by the extensional tectonics. MARINE AREAS In the marine areas, we distinguished different morphological environments, from beaches through the offshore (inner shelf), to the outer shelf and upper slope where two confined slope basins (Palermo and Termini basins, separated by the Monte Catalfano salient) represent the south-western margin of the large Cefalù basin. The substrate of these basins is represented by the Sicilian FTB tectonic units and their syn- and post-orogenic covers. The area shows a lateral variation from the rocky shores, in front of Monte Pellegrino and Monte Catalfano and in the eastern sector, to the beaches mainly in the central sector.190 Important physiographic changes, as shelf width and gradient and different coast orientations, characterise the continental shelf and slope and influence the hydrodynamic processes (wave activity and shelf current patterns). The continental shelf reaches 250 km2 and shows width values ranging from 1.5 km in the Capo Zafferano offshore to 8,0 km in the gulf of Termini, whereas gradient values range between 1° and 8°. The continental shelf has been subdi- vided into an inner infralittoral domain down to a 30 - 35 m water depth, which is characterized by an abrasion platform at different depths, and the outer shelf domain extends to the shelf edge. The shelf edge, which is both depositional and erosional, located at water depths between 120 m and 140 m, rises to lower depths at the canyon heads. Dominant morphological features along the continental slope are the submari- ne erosive conduits, locally interesting also the continental shelf. The heads of the conduits are characterised by severe episodes of retrogressive failure and incised by small gullies. Some (the Oreto and Eleuterio canyons) are directly linked to rivers and were connected during the last glacial maximum through incised val- leys, now buried by transgressive to highstand deposits. In the central sector of the Gulf of Palermo, we pinpointed almost three pockmarks, depressions tens of meters deep, originating from escaping fluids, while in the western sector of the gulf the same phenomena caused the occurrence of isolated or aligned, outcrop- ping or buried mounds. Finally anthropic features largely characterize the seabottom mainly in the inner shelf. seIsmostratIgraphy and stratIgraphIC settIng The buried sedimentary succession has been investigated by means of a close grid of single and multichannel seismic lines. On the whole, three seismic units (S, C and A) have been distinguished. The S seismic unit represents the offshore prolongation of the Meso-Cenozoic units of the Sicilian FTB and their syn- and post-orogenic cover. They are ge- nerally topped by a pronounced, erosive unconformity, correlated to the exten- sive Messinian horizon, generated during the last phases of the Mediterranean Salinity Crisis (5.5 Ma), and covered by a transparent seismic unit representing the Globigerina - bearing pelagic chalk (Trubi) and the Upper (?) Pliocene slope to shelfal deposits. The C seismic unit is represented by a prograding succession of 4° to 7° dip- ping horizons, which have been correlated with the regressive upper Pliocene- Pleistocene deposits, topped by the regional wide, erosional truncation related to the last glacioeustatic sea level fall, correlated with the δ18 O isotopic stage 2. The A seismic unit corresponds to the Late Pleistocene to Holocene 191 depositional sequence (SDTQ) with sigmoidal to tabular geometry; the deposi- tional sequence consists of a Falling Stage and Lowstand Systems Tracts with a progadational pattern controlling a relevant out-building of the shelf margin and a sedimentary wedge, of variable thickness, made up of the Transgressive (TST) and the Highstand (HST) Systems Tracts. The TST, developed during the Holocene sea level rise, shows a retrograda- tional stacking pattern, while the HST, deposited during the last 6 ka b.P., shows aggradational to faintly progradational geometries, related to the development of a littoral depositional system. Along the upper slope, turbiditic systems, characterized by erosive conduits and scattered mass wasting, developed extensively during the Late Pleistocene to Holocene. Surficial sediments of the continental shelf and slope The continental shelf and slope of the Palermo sheet are veneered with uncon- solidated, late Holocene in age, clastic and biogenic carbonate (Palermo gulf) and in second order, lithoclastic (Termini gulf) sediments. Deposits are composed of sands, relict Pleistocene and older carbonate parti- cles, abundant biogenic carbonate granules and algal-coated grains. In the outer shelf and upper slope, deposits are predominantly fine to very fine grained (silts and silty clays). The inner shelf is veneered by a mixture of gravel (rarely), coarse to fine sands, silts and clays, showing a general trend of decrea- sing size in a general seaward direction. From the sedimentary and the morphological features, four different depo- sitional systems have been distinguished: foreshore depositional systems, inner shelf depositional systems, outer shelf depositional systems and upper slope de- positional systems, mapped as g8 , g19 , g21 , m2 respectively. The systems are laterally gradational and linked by a variety of sedimentary processes. Shallow marine environments (up to a 50 m water depth) are generally characterized by biogenic sediments while terrigenous and carbonate clastic sedi- ments supplied by rivers or coastal erosion locally prevail. The most important facies of the infralittoral domain consists of Posidonia oceanica and Cymodocea nodosa meadows, which extensively cover the rocky substrate or the sandy floors the former and the muddy floors the latter. teCtonIC evoLutIon of the offshore areas The present day structural setting reconstructed in the Palermo sheet marine sectors appears the same as the tectonic edifice depicted on the mainland: it has 192 been interpreted as a consequence of the complex Neogene to Quaternary tectonic evolution. The compressive tectonics, responsible for the wedging of the present day submerged thrust sheets, developed during the Late Miocene span interval. This event was followed by transpressive tectonics that faulted and folded the Late Neogene to Pliocene infill by activation of high-angle, deep faults. During the Pleistocene, extensional tectonics accounted for opening and subsidence of structural lows. Present day active tectonics is still going on, as documented by compressive- transpressive focal mechanisms of shallow to deep, low amplitude earthquakes occurring along the offshore between the Sicilian coast and Ustica Island. A few middle-late Pleistocene marine terraces, outcropping along the coast at different levels, suggest a prolonged, faintly tectonic uplift. On the whole, the Plio-Quaternary geological evolution of the offshore area appears to be constrained by a strong interaction between eustatic sea level chan- ges, sediment supply and tectonics, recorded by strain features and enhanced un- conformities crossing the basin fill.

The exploitation of economic resources in marine environment and the assessment of natural hazards press a greater knowledge of the sea floor geology. Since the Structural Model of Italy was published in the 1991 by the CNR, new data have been collected concerning the marine geology of the sea floor surrounding Italy, also by means of up to date technologies (digital seismics, SBP Chirp, Multibeam). Data collected during the last decades in the frame of research programs as CROP MARE, CARG, morpho-bathymetric survey of the Tyrrhenian Sea, MAGIC, allow investigating the submerged geological structures with different temporal and spatial resolution. As consequence, at present marine geologists can draw geological maps where different geological features and related tectonic structures can be highlighted: 1) the depth of the Moho discontinuity; 2) the depth of the carbonate platform top; 3) the depth of the Messinian unconformity and the thickness of the Plio-Quaternary basin infill; 4) the Late Quaternary depositional sequence; 5) the main morpho-structural features (volcanoes, canyons, slides and slumps). Geological maps containing all of this information allow to define the submerged stratigraphic and structural setting and to reconstruct the geological evolution of the Italian sea floors, helping in to assess the marine geological hazard. The criteria for representation must be chosen so as to facilitate the correlation with the adjacent emerged areas. A particular attention will be paid to the late orogeny structures that controlled the Quaternary morphogenesis and mostly responsible for the present day morpho-structural setting of the Italian sea floor as well as the seismicity of this region. In this communication, a few geological map examples coming from the Sicily offshore will be shown to debate the scale and the most appropriate methodologies to be used for the representation of a new structural model of the Italian sea floor.

The geodynamics of the central Mediterranean is characterized by the interaction between the European plate and the African one. In this setting Sicily is a sector of the Appenine-Maghrebide accretionary prism, which is located between two areas affected by extensional tectonics (Sicily Channel to the south and the Thyrrenian back arc basin to the north). In the present study we present the first dataset of helium isotopic composition measured in fluids released from the central-western Sicily.With the aim to constrain the transfer system of fluids in this area we relate the results of geochemical investigations with the stratigraphy and structural setting, derived from field geology, deep boreholes and new seismic reflection, gravimetry and magnetometry data. Significant mantle-derived helium (0.4

The geodynamics of the central Mediterranean is characterized by the interaction between the European plate and the African’s. In this setting Sicily is a sector of the Appenine-Maghrebide accretionary prism, which is located between two areas affected by extensional tectonics (Sicily Channel to the south and the Thyrrenian back arc basin to the north). Significant mantle-derived helium (0.4

Mass wasting and downslope movements are common processes that have contributed to shape the northern Sicilian continental margin (southern Tyrrhenian Sea) since the Late Quaternary. Nevertheless, processes controlling their evolution are still partially unknown and a variety of geologic factors can be responsible for their formation. In this work we present an overview of the main mass wasting features (submarine canyons, landslides, debris flows) observed and mapped in different sectors of the northern Sicilian margin. The margin is characterized by a narrow, steep continental shelf (1-2°) and a very irregular and steep (6-8°) upper slope. The main aims of this work are: (1) to outline the morphology of the submarine canyons and of the related mass failure features, (2) to describe the main geological processes that control mass failure and (3) highlight their potential implications for the geo-hazard. The study is based on Multi Beam echosounder, Side Scan Sonar data and seismic reflection profiles, for a depth range of 20-1500 m, and on sediment samples and scattered gravity cores, collected to define the textural and compositional properties of the seafloor. Our study focused on the Castellammare Gulf-San Vito Trough system, the Gulf of Palermo, the Termini-Cefalù offshore and the Ustica offshore. In the Castellammare Gulf two main channel systems converge at the San Vito Canyon. This latter develops northwards with a very sinuous pattern, crossing the San Vito through. In the western margin of the Gulf, where the upper slope is very steep (12-13°) and the continental shelf is very narrow or absent, there are a lot of short, straight, sub-parallel gullies that are only few metres deep. In this sector the gully heads are located very close to the coastline and are associated to retrogressive slides. According to the aforesaid, downward erosive flows appear to be the most common mechanism generating widespread slope failure inside the Castellammare Gulf. In the Palermo Gulf a difference in slope configuration can be observed between western and central-eastern sector. Submarine canyons are confined to the upper slope or indent the shelf-edge and enter the Palermo intraslope basin at a depth of around 1,300 m. The canyons evolved through concurrent top-down turbiditic processes and bottom-up retrogressive mass failures. Most of the mass failure features of the area are related to canyon shaping processes. The western sector of the Palermo Gulf slope displays a highly dissected substrate, showing steep to very steep gradients, that appear to favour a retrogressive evolution of the canyons. Headward erosion processes are the main controlling factor in shaping this sector. NNE trending canyons occurring in the central-eastern sector develop in connection with the Oreto and Eleuterio rivers, breaching the shelf break, and show a linear to sinuous thalweg path. A similar pattern can be recognized in the eastern sector of the Termini-Cefalù offshore. The occurrence of pockmarks and carbonate mounds also suggests the probable role that fluid seeps play in the mass wasting processes of the area. Furthermore, the occurrence of pockmarks and highs that probably consist of authigenic carbonates above faulted and folded strata suggests a local relationship between structural control, fluid escape processes and mass failure. In the Ustica offshore volcanism related features (debris avalanche, gravitational collapse of volcanic edifices) are mainly linked to neotectonic activity and volcanism that tends to build, load and steepen the submarine slopes with time. This paper presents a valuable high-resolution morphologic dataset of the northern Sicily continental margin, which constitutes a reliable base for evaluating the geo-hazard potential related to slope failures in the area, through monitoring of areas where mass movement might be forthcoming and modelling landslides consequences to develop geohazard mitigation strategies.

New exploration in the marine environments has revealed that the fluid escape structures are often associated with neotectonic elements and are aligned along the same direction. Sometimes is observed the migration of fluid along fault planes to the sea floor as gas venting (Forrest et al., 2005). This paper aims to recognize and to classify the different types of structures associated with fluid seepage, particularly those that develop along alignments coinciding with or parallel to the neotectonic lineaments, in order to assess the interactions between tectonics and fluid circulation. The study area extends, from west to east, from the Gulf of Castellammare to the Gulf of Termini (offshore northern Sicily), and belongs to the northern Sicily continental margin, in the transitional area between the Sicilian-Maghrebian Chain to the south and the southern Tyrrhenian Sea to the north. Previous morphostructural studies identified a wide W–E trending right-lateral shear zone, mainly characterized by both a synthetic NW-SE/W–E trending, and antithetic left-lateral N–S/NE-SW fault systems, which affected the tectonic edifice, since the Pliocene (Giunta et al., 2009), while the current seismicity shows compressional focal mechanisms aligned to the NW-SE and ENE-WSW trends, in agreement with axis of maximum horizontal compression oriented NW-SE (Neri et al., 2003). We used a dataset of seismic reflection profiles, both high and very high resolution single-channel and multi-channel profiles, acquired respectively with CHIRP, sparker and airgun sources, and high resolution morphobathymetric data acquired down to 2200 m, in relation to the MaGIC project (Marine Geohazards along the Italian Coasts). The data allowed us to distinguish three different types of fluid escape structures by means of highly contrasting seismic and morphologic signatures. In particular, mounds and buried mounds have been recognized in the continental shelf, while pockmarks occur in the continental slope; the latter are often found to be aligned in this area. Two fault systems have been recognized: a NW-SE trending extensional and/or transtensional system, which produces the recent articulation of the seabed, and an ENE-WSW trending compressive, which contributed to the formation of morphological relieves. The seismicity of the area confirms the recent activity of both the systems, because the clusters of earthquakes of 1998, 2002 and the most recent until 2011 (http://www.ingv.it), are aligned with the recognized tectonic structures, and have focal mechanisms with major compression horizontal axis oriented NW-SE, compatible with the orientation of the tectonic lineaments. The identification of fluid escape structures, aligned with the neotectonic lineaments and with the clusters of earthquakes, allows us to hypothesize the relationship between the circulation of fluids and faults, the latter being preferential pathways for the rapid ascent of the fluid towards the surface. Moreover, the recent seismic activity indicates that the recognized neotectonic structures, respectively oriented NW-SE and ENE-WSW, are active and especially seismogenic structures.

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.

MaGIC è un progetto quinquennale (2007-2012) finanziato dal Dipartimento Nazionale della Protezione Civile per l'acquisizione di dati morfobatimetrici ad alta risoluzione. Lo scopo principale del progetto è quello di definire e rappresentare i principali elementi morfologici dei fondali marini, in particolar modo quelli derivanti da dinamiche morfo-sedimentarie che implicano mobilità e/o instabilità dei sedimenti e conseguenti situazioni di pericolosità per le infrastrutture e le aree costiere urbanizzate. I rilievi morfobatimetrici vengono realizzati con un sistema ecoscandaglio radiale multifascio (Multibeam echosounder systems) calibrato ad hoc nell’area di lavoro e corretto in velocità mediante sonda in continuo (SVPC) e profilo verticale della velocità del suono (SVP). I dati batimetrici acquisiti sono inizialmente elaborati e filtrati, attraverso appositi software, e successivamente vengono esportati in maniera tale da poterli interfacciare con altre piattaforme software GIS. Il software Global Mapper è utilizzato per l’interpretazione dei dati e la realizzazione di modelli digitali 3D. Tale software è stato implementato di specifici tools realizzati unicamente per il progetto Magic dalla casa produttrice. Vengono mostrate immagini dei fondali marini del settore centro occidentale del margine continentale nord-siciliano (offshore di Palermo) e delle morfologie sommerse dell’edificio vulcanico dell’Isola di Ustica, che evidenziano le aree a maggiore rischio geologico.

The Bay of Augusta is located along the NE margin of the Hyblean Plateau (SE Sicily). In this area a mostly bioclastic and terrigenous Quaternary succession outcrops. This area recorded a constant regional uplift rate of 50 kA. Two main groups of faults, referred to as the northwest and the southwest fault zones, are separated by a central zone where no evident fault planes have been imaged by seismic data. The faults in both groups strike from N30W to N52W and are also inferred to be steeply dipping. The faults pertaining to northwestern cluster show a very little offset, < 15 m. These faults have displaced mostly seismic unit C and have controlled two, NW-SE trending little structural lows in the central and in the northernmost sectors of the investigated area. These restricted basins have been filled by B and A seismic units deposits that don’t appear displaced by the fault cluster. The southeastern fault zone is long less than 700 m and show an offset of 1 to 5 m. These faults displaced the horizons of seismic Unit C in a sector where this unit outcrops at the sea bottom or it is draped by a very thin veneer of Unit A sediments. The faults pertaining to the northwestern zone post-date Unit C but they appear older than Units B and A.Radiocarbon age-dating have demonstrated that the most recent horizons involved in the northwestern fault zone displacement is > 50 kA. As concern the southeastern fault zone, results coming from radiocarbon age dating don’t have sufficient resolution to correlate deposits to seismic horizons involved in tectonic deformation. Nevertheless, there the seismic unit A also appears slightly involved by the latest faults activity. The analysis of the Bay of Augusta seismic grid has shown that very recent tectonic features have displaced the Late Quaternary sedimentary infill; interpretation of our results could better constrain the neotectonic setting of an area characterized by high seismic hazard.

The occurrence of mud volcanoes and mud domes is, for the first time, documented in the continental shelf and upper slope of the Palermo and Termini Gulf (north Sicily offshore region). The study area belongs to the northern Sicily continental margin (southern Tyrrhenian Sea). Along this margin, morphology of the high-gradient continental slope is irregular due to the presence of structural highs, slope failures and canyons, and is interrupted by a flat area at a depth of 1,500 m. Mud volcano activity generally formed in areas characterised by high sedimentation rates and/or as consequences of regional tectonics (often compressional), overpressure in the sediments and gas generated at different depths. Materials and methods This study is based on unpublished, near-vertical seismic profiles shot in 2001 in the N Sicily offshore region, coupled with multichannel seismic profiles and multibeam data. The latter have been acquired using the 50-100 kHz Seabat instrument, with operating depths ranging from 50 to 1500 m, and processed with the software PDS 2000. Seismostratigraphic analysis tools and methods were used to identify mud volcanoes and to make classification on the basis of their morpho-acoustic characteristics. The detailed 3D bathymetric chart was used to define the top view morphologic features and their areal distribution. Results The new data show the occurrence of three types of structures with highly contrasting seismic and morphologic signatures: • dome-type structures (type 1), elevating 5 to 30 m from the seafloor, showing transparent to chaotic internal facies with mound external geometry (locally with a central depression), and deforming the adjacent reflectors; • concave-upwards structures (type 2), depressed 5 to 20 m from the seafloor, showing at depth layered concave-upwards pattern or locally chaotic convex-upwards pattern. Their top view is a circular aligned areas known as pockmarks; • buried structures (type 3), showing chaotic to transparent facies, and deforming the adjacent reflectors; these structures appear to be buried by recent deposits. Type 1 structures are recognized in the whole investigated shelf areas and are prevalent in the Palermo Gulf western margin (Pellegrino Mt. offshore); type 2 formed near the shelf margin, whilst the type 3 structures occur only in the Termini Gulf. In the we recognise type 1 structures only. Our data integrated with stratigraphic and structural data available in literature for the North Sicily offshore suggest that mound structures (type 1) area associated with fault planes, that are widespread offshore Pellegrino Mt. We interpreted these structures as mud domes associated with diagenetic carbonates and fluid venting activity. The pockmark structures (type 2) could be the result of both fault and landslide structures, as they appear aligned along straight direction and occur in proximity of the slope, associated with slope instabilities. The buried structures (type 3) occur in the Termini offshore where the higher sedimentation rate supports the sealing of the mud flow.