Search

The Marsili Seamount (MS) is a 70 x 20 km extended, NNW-SSE elongated volcanic complex rising 3200 m from the seafloor of the Southern Tyrrhenian Sea (Italy) and with the top at ca. 500 m b.s.l.. MS represents the inflated spreading ridge of the 2 Ma old Marsili back-arc basin (BAB) formed in the last 1 Ma on a 10 to 12 km thick oceanic crust and associated to the Ionian Sea subduction below the Calabrian Arc. MS last erupted 2-3 ka BP, and it is now characterized by shallow seismicity and hydrothermal activity. In a previous study of a 25 x 25 m Digital Bathymetric Model (DBM) of MS, some authors have identified signs of seafloor failures and coexisting central-type and fissural volcanoes with prevailing passive magma ascent mechanisms mainly controlled by tectonics. Here we present a morphometric and morphological analysis of a high resolution (5 m x 5 m) DBM of the Marsili seamount in order to: (a) identify its detailed morphological and geological features and (b) better understand how volcanoes, overlapping and/or segmented spreading centres, and faults interact and control the growth and evolution of BAB ridges. Our results emphasize the importance of high-resolution bathymetry data in deciphering the geodynamic evolution of BAB. The results may also help to individuate sites of hydrothermalism and identify areas where landslides or flank/sector collapses occurred in the past and, eventually, could develop in the future., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Framed in the current geodynamics of the central Mediterranean, the Aeolian-Tindari-Letojanni fault system is part of a wider NW-SE oriented right-lateral wrench zone which accommodates diverging motion between regional-scale blocks located at the southern edge of the Calabrian Arc. In order to investigate the structural architecture and the active deformation pattern of the northern sector of this tectonic feature, structural observations on-land, high and very-high resolution seismic reflection data, swath bathymetry data and seismological and geodetic data were merged from the Lipari-Vulcano volcanic complex (central sector of the Aeolian Islands) to the Peloritani Mountains across the Gulf of Patti. Our interpretation shows that the active deformation pattern of the study area is currently expressed by NW-SE trending, right-transtensional én-echelon fault segments whose overla ing gives rise to releasing stepover and pull-a art structures. This structural architecture has favored magma and fluid ascent and the shaping of the Lipari-Vulcano volcanic complex. Similarly, the Gulf of Patti is interpreted as an extensional relay zone between two overlapping, right-lateral NW-SE trending master faults. The structural configuration we reconstruct is also supported by seismological and geodetic data which are consistent with kinematics of the mapped faults. Notably, most of the low-magnitude instrumental seismicity occurs within the relay zones, whilst the largest historical earthquakes (1786, Mw=6.2; 1978, Mw=6.1) are located along the major fault segments.

In this study, we present the results of a very high-resolution bathymetric survey carried out offshore the dismissed industrial site of Bagnoli (Pozzuoli Bay, Gulf of Naples). The bathymetric maps and the thematic representation produced, allowed for detailed characterisation of the seabed lineaments and features. Seafloor bedforms and morphological features can be observed at a very high resolution. Moreover, the potential pattern of sediment transport can be inferred from the seafloor bedforms observed in the central sector of the surveyed area. The new morphobathymetric map of Bagnoli-Coroglio offshore provides a valuable tool for stakeholders towards a comprehensive planning and management addressed to environmental revaluation and rehabilitation of this disused industrial area.

The Palinuro volcanic chain is located nearly 80 km offshore the Campania coasts (Italy), in the southern sector of the Tyrrhenian Sea. 15 distinct volcanic edifices have been recently detected. The presence of shallow seismicity and active hydrothermal activity suggests that this large volcanic chain is still active. Specific sectors of the complex show the existence of ongoing slope instability. Thus, the chance of mass movements following seismic or volcanic activity cannot be ruled out. Stability analysis for typical seismic loads in such a volcanic area has been performed. Three mass failure scenarios have been reconstructed through numerical models in the weaker sections found. The tsunami triggered by each slide has been simulated, and large waves have been found in two of the three hypothesized scenarios. For the biggest slide of 2.4 km, waves as high as 6 m could reach portions of the Calabria region coasts.

Subduction-transform edge propagators are lithospheric tears bounding slabs and back-arc basins. The volcanism at these edges is enigmatic because it is lacking comprehensive geological and geophysical data. Here we present bathymetric, potential-field data, and direct observations of the seafloor on the 90 km long Palinuro volcanic chain overlapping the E-W striking tear of the roll-backing Ionian slab in Southern Tyrrhenian Sea. The volcanic chain includes arc-type central volcanoes and fissural, spreading-type centers emplaced along second-order shears. The volume of the volcanic chain is larger than that of the neighbor island-arc edifices and back-arc spreading center. Such large volume of magma is associated to an upwelling of the isotherms due to mantle melts upraising from the rear of the slab along the tear fault. The subduction-transform edge volcanism focuses localized spreading processes and its magnitude is underestimated. This volcanism characterizes the subduction settings associated to volcanic arcs and back-arc spreading centers., The volcanism of subduction settings concentrates in island-arcs and back-arc basins. Here, the authors show that the lithospheric tear faults bounding roll-backing slabs may focus huge volcanism with a volume of the erupted products exceeding that of the island-arcs edifices and back-arcs spreading centres.

In order to properly adopt the international recommendations on the marine environment and biodiversity conservation, as well as fishing resources and human health, an increasing effort is incoming in the last two decades to study, prevent and mitigate the anthropogenic environmental impact in the Mediterranean sea. The main research efforts and policy strategies implemented in the last two decades are regarding oil pollution (dumping, spills, shipping, extraction, accidents, etc.), civil and industrial waste discharges and, recently, littering. Less known are the other pollution sources generally not visible and frequently distributed offshore. One of this cryptic sources of pollution is represented by military and commercial shipwrecks abandoned on the sea bottom. Actually, fuels, construction materials, army and transported goods deposited at the bottom of the sea can generate ecological damage thus modifying natural biological diversity and fishing activity with unpredictable hazards and dangerous effects on the marine ecosystem. In particular, indiscriminate and uncontrolled leakage of toxic material and organic/inorganic pollutants from those vessels could affect the wellbeing of the deep sea also for long-time. Very few data are available on the effects of pollution produced by shipwrecks in the Mediterranean sea although thousand of military ships were abandoned at the seabed of the basin as effect of accidents during the first and the second word wars. This contribution aims to explore the potential effects of contamination of a number of shipwrecks identified by multi-proxy geophysical tools at the bottom of one of the key areas of the Mediterranean sea, around the Sicily island, where intense ship traffic and fishing activities occur. Geophysical exploration and geochemical data (heavy metals, PAHs, PCBs, Pesticides, hydrocarbons, etc.) are here presented for selected cases and testify the high risk represented by this kind of point-source pollution on the marine system. © 2013 by Nova Science Publishers, Inc. All rights reserved.

The onset of new technologies in marine data acquisition, processing and interpretation of the Naples Bay (Southern Italy) is herein discussed, focussing on the contribution of seismo-stratigraphic and marine magnetic data. Seismic stratigraphy and marine magnetics of selected case histories of the Somma-Vesuvius offshore, Phlegrean Fields offshore and Ischia-Procida volcanic complex are here shown. Seismic exploration is commonly performed by means of sources that can generate elastic waves from a rapid expansion of underwater gas bubbles. This can generate many pulses that take the form of double exponential spikes of gradually decreasing amplitude (Cole, 1965). Several technologies can be used in order to produce an acoustic pressure wave into water, such as free-falling weights, chemical explosives, piezoelectric or magneto-resistive sources, sparkers, boomers, air-guns and water-guns. Each of these sources has precise signature and wave frequency that can be considered optimal in function of depth, resolution, etc. The main characteristics of a seismic source is to produce a single high-energy spike that is detectable, despite the presence of noise, after crossing the portion of the seabed that we wish to study. A broad range of frequencies can be reproduced, as well as a broad range of waveforms can be generated in function of frequency-dependent absorption of elastic waves and nearby boundaries presence. Seismic sources for offshore investigation may be impulsive, providing a short-lived burst of elastic wave energy and swept-frequency, producing a low-amplitude sinusoidal signal. Impulsive sources such as explosives can cause damages to marine flora and fauna; for this reason towed sources activated for only few seconds must be preferred. The type of source could be chosen depending on the required resolution and signal penetration. Vibration of piezoelectric and magnetic materials, electric pulses, or pressured fluid discharge, often organised into arrays, can be considered good seismic sources whose signature, spectra and energy output can vary considerably. Sparkers (Knott and Hersey, 1956) and Boomers (Edgerton and Hayward, 1964) systems are based respectively on an electrode array powered by high voltage capacitor bank and on an electromagnetic source. Sparkers and boomers can generate seismic energy to explore continental margin when there are near surface or deep-towed (10-50 m off the sea), moreover boomers with pulse length of 0.1-0.2 ms can be used to explore very shallow waters. Sparker system can produce low-frequency acoustic wave (the maximum frequency contained in the spectrum of acoustic signal is approximately 2000 Hz) that can penetrate several hundred meters of sediment. One of the most interesting seismic sources is the Multispot Extended Array Sparker (M.E.A.S.) that consists of sparker electrodes disposed on a square metal cage. This kind of system, patented by Institute of Oceanology of Istituto Universitario Navale of Naples (Italy) allows obtaining a good signal penetration and high resolution seismic data with relative small energy use. The M.E.A.S. signal is a short impulse with a large frequency spectrum content (Fig. 1). Mirabile et al. (1991) tested the acquisition geometry in order to reduce a superimposing of source signal with return echoes that respect the "far field" condition and demonstrated the utility of some techniques for signal de-convolution in order to produce the so-called seismic profiles "deghosting". Seismic reflection data require a complex series of numerical treatments to increase the signal/ noise ratio of a single profile as well as obtaining a high resolution seismic section to improve the geological interpretation. A more recent technology is the Sparker source SAM that is characterized by a varying number of electrodes that can be disposed as "dual-in line" (SAM96) and "planar array" multi electrode electro-acoustic source (SAM 400/800; Fig. 2). Other seismic sources are the Airguns and Waterguns, recently used in the Naples Bay in submarine geological mapping and basin studies (D'Argenio et al., 2004; Aiello et al., 2005; 2011). The former one produces high-energy seismic pulses short in duration by means of a discharge of compressed air into water (Fig. 3), while the latter one produces the sudden collapse of a cavitation volume into water that is proportional to kinetic energy of the water plug. Airguns produce a wide range of pulse shapes and source spectra. The seismic exploration of Naples Bay has been performed mainly through Sparker systems and Watergun sources. The evolution of sources capability in terms of technological advances together with processing techniques refinement allowed high resolution studies of main intermediate and deep geological structures in the Bay of Naples. Historically some of the first surveys were conducted by R/V Atlantis II (Woods Hole Ocean. Cruse 59) using an Airgun System. Subsequently, in 1970 R/V Dectra owned by Istituto Universitario Navale of Naples (Italy) obtained a densely-spaced seismic survey through SPARKER E.G.G. (8 kjoules) and BOOMER systems in the Naples and Pozzuoli Bays (Latmiral et al., 1971; Bernabini et al., 1973). Since the 70's until now many attempts have been carried out in order to improve seismic technologies performance, data acquisition, and processing. In the practice of seismic prospecting, Sparker systems technologies were widely analyzed using different acquisition systems. Some ones consist of a single electrode hotter than a mass electrode, other ones of more electrodes over distributed mass (eg. Sparker Teledyne and Sparker EGG). De Vita et al. (1979) tried to identify, also based on experimental data, which one is more appropriate than the two configurations (single electrode or multi-electrode) based on the fundamental equations for the design of an "array". Sparker signals are the base band signals, transitory and continuous spectrum. Based on these measurements it has been demonstrated that energy should never exceed 400 joules/electrode to achieve the best compromise between resolution and electro-acoustic performance. Ranieri and Mirabile (1991) reported technical and scientific results obtained through the geophysical survey of the deep geological structure of the Phlegrean Fields volcanic complex. It was aimed at improving the knowledge on technologies and sources that are more appropriated for the investigation of the continental margins, particularly in complex volcanic areas like the Gulf of Naples (Fusi et al., 1991). Among the sources tested in studies of the Gulf of Naples there are the explosives (Mirabile et al., 1989), the Sparker and the Watergun, while the details to study geomorphological data were analyzed through the Surfboom and the Side Scan Sonar. MEAS (Multispot Extended Array Sparker; Mirabile et al. , 1991) seismic source (12 and 16 KJ), consists of an array of 36 (6x6) electrodes placed inside a metal cage in a square size 4.5x4.5 m, spaced 0.75 m and fed in phase. The energy used by the MEAS has a pulse of short duration, the order of 10 milliseconds and a significant spectral content up to 1000 Hz, with maximum energy output around 150 - 200Hz. Each echo corresponds to an acoustic discontinuity (impedance contrast) that can generally be interpreted in geological terms. MEAS system has been largely used in order to acquire a large database of single channel reflection seismics in the Bay of Naples (Mirabile, 1969; Latmiral et al., 1971; Mirabile et al., 1991). Recently, by means of Multi- tip SAM 96 (0.1-1kJ), SAM400 (1-4KJ) transducer it was possible to record high resolution seismic data in the Bay of Naples both in coastal and deep sea research (Corradi et al., 2009). Some evidences on magnetic field anomalies in the Gulf of Pozzuoli come from the magnetic map of Galdi et al. (1988) who reported a NE-SW interruption of main regional trend where some circular local anomalies are related to products of post-calderic volcanic activity (Rosi & Sbrana, 1987). Significant correlations between geophysical data come from the comparative analysis of seismic and magnetometric datasets. A magnetometer usually measures the strength or direction of the Earth's magnetic field. This last can vary both temporally and spatially for various reasons, including discontinuities between rocks and interaction among charged particles from the Sun and the magnetosphere. Most technological advances dedicated to measure the Earth's magnetic field have taken place during World War II. Presently, the most common are: the fluxgate, the proton precession, Zeeman-effect, sensor suspended-magnet, and satellite magnetometers. The fluxgate and the proton precession are effectively the most used for marine surveys, they are both cable drawn. The fluxgate magnetometer was the first ship-towed instrument, and it can measure vector components of the magnetic field. Its sensor consists of two magnetic alloy cores that are mounted in parallel configuration with the windings in opposition. The proton precession magnetometer consists of a sensor containing a liquid rich in protons surrounded by a coil conductor, the sensor is towed from the vessel through an armoured coaxial cable whose length depends on vessel length and seafloor depth. Circulating current within the coil generates a magnetic field of approximately two orders of magnitude the Earth's field, in this way 1 proton each 10 will follow the coil positioning. Stopping the induced magnetic field, the protons will align according to the Earth's magnetic field through a movement of precession. The proton precession magnetometer is one of the most used for offshore surveys and it records the strength of the total field by determining the precessional frequency (f) of protons spinning about the total field vector (F) as follows: f=?pF/2?????? where ?p is the gyromagnetic ratio of the proton uncorrected for the diamagnetic effect, so that knowing its from laboratory measurements, the total field in nanotesla can be calculated as: F=23.4866 x f (2) ? The total field calculated by means of equation (2) is stored by magnetometer into a string of data containing position data that is displayed as an x,y chart. The signal frequency is measured on a time span of 0.5 seconds when the signal-noise ratio is highest. To ensure a maximum value of initial value of proton precession the angle between the axis of the coil and the Earth's field it is necessary to use two orthogonal coils. The measured field must be corrected with respect to the regional field in order to evaluate the anomalies. The proton precession magnetometer was largely used to explore magnetic anomalies in the Bay of Naples. Interesting examples of magnetic data acquisition related in the Bay of Pozzuoli and Naples is reported in Galdi et al. (1988) and Aiello et al. (2004). As shown by the maps of Galdi et al., 1988 both positive and negative anomalies were detected, using a magnetometer model Geometrics G-856, globally the area shows an interruption of the regional trend from NE-SW where circular anomalies are probably connected to a post-calderic activity of the Phlegrean Fields. Moreover, the internal area of the Pozzuoli Bay is characterized by a negative anomaly that increases towards the south. Conversely, in the external area there is mainly an alternance of positive and negative anomalies with a dominance of positive values near the area of Bagnoli. For a detailed analysis of the magnetic anomaly field of the volcanic district of the bay of Naples see Secomandi et al. (2003). Recently, Aiello et al. (2004) presented a high resolution map of the Bay of Naples based on data acquired during oceanographic cruise GMS2000-05 performed in October-November 2001 on board of the R/V Urania using the EG&G Geometrics proton magnetometer G-811. REFERENCES Aiello G., Angelino A., Marsella E., Ruggieri S., Siniscalchi A. (2004) Carta magnetica di alta risoluzione del Golfo di Napoli (Tirreno meridionale). Bollettino della Società Geologica Italiana, 123, 333-342. Aiello G., Angelino A., D'Argenio B., Marsella E., Pelosi N., Ruggieri S., Siniscalchi A. (2005) Buried volcanic structures in the Gulf of Naples (Southern Tyrrhenian sea, Italy) resulting from high resolution magnetic survey and seismic profiling. Annals of Geophysics, 48 (6), 883-897. Aiello G., Cicchella A.G., Di Fiore V., Marsella E. (2011) New seismo-stratigraphic data of the Volturno Basin (northern Campania, Tyrrhenian margin, southern Italy): implications for tectono-stratigraphy of the Campania and Latium sedimentary basins. Annals of Geophysics, 54 (3), 265-283. Bernabini M., Latmiral, G., Mirabile, L. & Segre, A.G. (1973). Alcune prospezioni sismiche per riflessione nei Golfi di Napoli e Pozzuoli. Rapp. Comm. Int. Mer. Medit., 21, 929-934. Cole R.H. (1965) Underwater Explosions. Dover Publications, New York. Corradi, N.; Ferrari, M.; Giordano, F., Giordano, R., Ivaldi, R. & Sbrana, A. (2009) SAM source and D-Seismic system:The use in Marine Geological Mapping C.A.R.G and P.n.r.a projects. 27th IAS Meeting of Sedimentologists, Alghero (Italy), pp. 85-90. D'Argenio, B.; Aiello, G., de Alteriis. G., Milia, A., Sacchi, M. et al. (2004). Digital Elevation Model of the Naples Bay and adjacent areas, Eastern Tyrrhenian sea, In: Mapping Geology in Italy, E. Pasquarè & G. Venturini (Eds.), APAT, National Geological Survey of Italy, Spec. Vol. SELCA, Florence, 22-28. De Vita S., Esposito B., Mirabile L. (1979) Criteri di Progetto di Sparker a cortina per sismica ad alta risoluzione. Atti del convegno Scientifico Nazionale Progetto Finalizzato Oceanografia e Fondi Marini. Edgerton H.E. and Hayward G.G. (1964). The boomer sonar source for seismic profiling. Journal of Geophysical Research, Vol. 68, pp. 3033-3042. Fusi, N., Mirabile, L., Camerlenghi, A. & Ranieri, G. (1991). Marine geophysical survey of the Gulf of Naples (Italy): relationship between submarine volcanic activity and sedimentation. Memorie della Società Geologica Italiana, 47, pp. 95-114. Galdi, A., Giordano, F., Sposito, A., Vultaggio, M. (1988) Misure geomagnetiche nel Golfo di Pozzuoli: Metodologia e risultati. Atti del 7° Convegno GNGTS-CNR, Vol.3, pp. 1647-1658. Knott, S.T., Hersey J.B. (1956) Interpretation of high resolution echo-soundings techniques and their use in bathymetry, marine geophysics and biology. Deep Sea Research, Vol.4, pp. 36-44. Latmiral, L., Segre, A.G., Bernabini, M. & Mirabile, L. (1971). Prospezioni sismiche per riflessione nei Golfi di Napoli e Pozzuoli ed alcuni risultati geologici. Bollettino della Società Geologica Italiana, Vol.90, pp.163-172. Mirabile L. (1969). Prime esperienze di stratigrafia sottomarina eseguite presso l'Istituto Universitario Navale. Annali IUN, Vol. 38. Mirabile, L., Nicolich, R., Piermattei, R. & Ranieri, G. (1989). Identificazione delle strutture tettonico-vulcaniche dell'area flegrea: sismica multicanale del Golfo di Pozzuoli. Atti del 7° Convegno GNGTS, Vol.2, Roma, Italy, pp. 829-838. Mirabile, L., Fevola, F., Galeotti, F., Ranieri, G.& Tangaro, G. (1991). Sismica monocanale ad alta risoluzione con sorgente multi spot di tipo sparker: applicazione ai dati di tecniche di deconvoluzione. Atti del 10° Convegno GNGTS-CNR, Roma, Italy. Ranieri G. and Mirabile, L. (1991). Ricerca ed applicazione di metodi geofisici al rilievo sperimentale della struttura medio-profonda dell'area flegrea con uso di sorgenti sismiche water-gun. Annali Istituto Universitario Navale di Napoli, Vol.63. Rosi M. and Sbrana A. (1987). Phlegrean Fields. Quaderni De La Ricerca Scientifica, CNR, Vol.114, No9, 175 pp. Secomandi M., Paoletti V., Aiello G., Fedi M., Marsella E., Ruggieri S., D'Argenio B., Rapolla A. (2003) Analysis of the magnetic anomaly field of the volcanic district of the Naples Bay. Marine Geophysical Researches, 24, 207-221.

THE VOLCANIC COMPLEX OF THE ISCHIA ISLAND: NEW GEOLOGICAL DATA ON SOUTHERN ISCHIA CANYON SYSTEM BASED ON SPARKER SEISMIC STRATIGRAPHY G. Aiello (1), E. Marsella, S. Passaro (1) (1) IAMC-CNR, Sede di Napoli, Napoli, Italy 1. INTRODUCTION New geological data on the volcanic complex of the Ischia island (Naples Bay, southern Italy) are here presented in order to constrain the Ischia geologic evolution during Quaternary times. The south-eastern offshore has been mainly investigated, among the southern continental slope of Ischia and Ischia Channel. A strictly-spaced grid of seismic sections has been recently acquired and interpreted in the frame of research programs of marine cartography (CARG Project) financed by the Campania Region (Sector of Soil Defence, Geothermics and Geotechnics) during the mapping of the marine areas of the geological sheet n. 464 "Isola d'Ischia" at the scale 1:25,000. Some of the collected seismo-stratigraphic data are here interpreted and discussed (Aiello et al., 2009a; 2009b; 2012). The seismic grid was recorded using a Sparker Multitip seismic source. The marine data acquisition and the related mapping around the Ischia island were performed down to the 200 m isobath (Geological Map n. 464 "Isola d'Ischia"; scale 1: 25,000; 2010; in press; Aiello et al., 2009b). The marine geological mapping offshore the Campania region was accomplished under the direction of Prof. B. D'Argenio and in part Dott. E. Marsella. Marine geological survey of the southeastern Ischia offshore at water depths ranging between 30 m and 200 m has been carried out by Dott. Gemma Aiello on the basis of data collected at sea. The seismic grid is composed of 13 dip seismic lines in the southern Ischia offshore, running perpendicularly to the shoreline and 2 tie lines, parallel to the shoreline (Fig. 1). The geological interpretation of seismic lines that cover the southeastern offshore of the island, from Punta Imperatore (southwestern Ischia) to the Aragonese Castle (eastern Ischia) has been carried out (Fig. 1). Seismic acquisition was carried out using a multielectrode Sparker system (SAM96 model). The advantages of the Multitip Sparker include shorter pulse lengths for an equivalent energy discharge, as well as a increase in peak pressure, i.e. the amplitude of the outgoing acoustic wave. The sparker source used in this survey generated 200 J in the 200-2,000 frequency range. Ship positioning was determined using a GPS system with an accuracy of 1 m. All the seismic sections were recorded graphically on continuous paper sheets with a vertical recording scale of 0.25 s. The best vertical resolution was approximately 1 m for the sparker data. The proposed stratigraphy derives from the type of data utilized in marine geology (reflection seismics) and from the methods of seismic interpretation (high-resolution sequence stratigraphy). The geological structures recognized through the seismic interpretation are acoustically transparent seismic units, representing the volcanic acoustic basement and the system tracts of the Late Quaternary depositional sequence (Fabbri et al., 2002). The depositional systems, referred respectively to the sea level fall (FST; Helland-Hansen and Gjielberg, 1994), sea level lowstand (LST) and related internal subdivisions (Posamentier et al., 1991), transgressive phase (TST; Posamentier and Allen, 1993; Trincardi et al., 1994) and sea level highstand (HST) have been identified in the Late Quaternary depositional sequence of the Ischia offshore through seismo-stratigraphic analysis (Catuneanu, 2006; Catuneanu et al., 2009). 2. GEOLOGICAL SETTING OF THE PHLEGREAN ISLANDS (ISCHIA AND PROCIDA) 2.1 Geology and marine geology The study area pertains to the Eastern Tyrrhenian margin, located on a continental lithosphere thinned and transitional towards the oceanic area which characterizes the Tyrrhenian bathyal plains, deep about 3500 m. The lithospheric extension of the Campania Tyrrhenian margin started since the Early Pleistocene and manifested in the upper crust as a strong vertical tectonics and uprising of magmas with volcanism. The Campania Plain may be considered as a depression resulting from the downthrowing of the Meso-Cenozoic carbonatic basement, representing the bulk of the Apenninic chain. Along the coastal profile this basement crops out in the Sorrento Peninsula as a NW dipping monoclinalic structure and crops out another time at the Massico Mt (to the north of the Volturno river). The magma uprising is happened along counter-Apenninic (NE-SW) directions, perpendicular to the general axis of the Apenninic chain, as in the case of the ridge Ischia-Procida-Phlegrean Fields. The Naples Bay is bounded eastwards by several monogenic volcanoes aligned along a ENE-WSW regional strike, running from the Ischia island to the Phlegrean Fields, passing towards the Procida island. The origin of the magmas is common with that one of the Neapolitan volcanoes, with alkali-potassic magmas, further subdivided in ultra-potassic and potassic ones. The ultra-potassic magmas are characterized by a high content of K20, translating as leucitic lavas (leucitites and leuco-tephrites) for the Somma-Vesuvius and siliceous lavas, as the trachytes, the alkali-basalts and the latites, which are characteristic of Ischia, Procida and Phlegrean Fields. In the local framework of the Phlegrean-Ischian magmatism the rate of differentiation may be more or less high depending on the time of resilience in the magmatic tanks, on their depth and on the immission of fluids. This has provoked the discrete heterogeneity of the petrographic types, including alkali-basalts, latites and hyperalkaline trachytes. If we exclude some great ignimbritic eruptions, happened in the Campania region each 20 ky about (Green Ignimbrites of Ischia, 55 ky B.P.; Campanian Ignimbrites, 35 ky B.P.; Neapolitan Yellow Tuff, 12-15 ky B.P.) the most part of the explosive events may be considered of middle-little entity. Most part of the eruptions has not produced lavas, excluding the uprising phenomena along intrusions (dykes) and domes, which a characteristic redundant and dominant of the volcanology of Ischia and rare lava domes at Procida and in the Phlegrean Fields, where, on the contrary, the hydromagmatic features predominate. 2.2 Striking of the main eruptive centres and vertical motions The alignment of eruptive centres giving origin to the Phlegrean islands fits to two main counter-Apenninic structural directions: the first one, which seems to be older, is E-W oriented, while the second one is ENE-WSW oriented, as the Ischia-Procida-Phlegrean Fields lineament. Also in the Ischia Channel and in the surrounding areas, both the trending of the marine topography and the distribution of the submerged and cropping out eruptive centres well fits to the same ENE-WSW regional trend. To the regional deformation it has to be added the interference of the local stress field, which, in the Ischia island, is dominated by the uplift of the Epomeo block, along perimetral faults, N-S, E-W and NW-SE trending (Acocella and Funiciello, 1999; Tibaldi and Vezzoli, 1998). Several geomorphologic indicators (uplifted marine terraces and fossil beaches; Cinque et al., 1997) testify phenomena of subsidence and uplift in several sectors of the Ischia island, which allowed for a whole uplift of the Epomeo block of about 700 m, both previous than successive to the emplacement of the Green Tuffs (55 ky B.P.). Based on geochronological data Gillot et al. (1982) have dated the uplift of the Epomeo Mt. at 33 ky B.P. 2.3 Marine geomorphology The Phlegrean Fields represent a physiographic division, more than geographic, among the Gaeta Gulf to the north and the Naples Gulf to the south. In fact, the volcanic complex Ischia-Procida-Phlegrean Fields is localized in correspondence to a main structural element, ENE-WSW trending, which has controlled the elongation of the main eruptive centres. In the study area three main physiographic domains are included, i.e. the continental shelf, located between the shoreline and the 140-150 m isobath; the upper continental slope, located between the shelf break and the - 600 m isobath; the lower continental slope, located at more than 600 m of water depth. These domains are joined by the main canyons (Magnaghi canyon, Cuma canyon) or their tributary channels (debris channels). The continental shelf has a low gradient and depositional shelf edge at water depths of 150-170 m, sometimes eroded. The elongation Ischia-Procida-Monte di Procida constitutes a morphological barrier between the continental shelf of the Gaeta Gulf and the Naples Bay, characterized by greater water depths. This morphological saddle is interrupted in correspondence to the Ischia and Procida islands. In these passages a great transit of water masses and sediments happen and high hydrodinamics on the submerged banks, as on "Le Formiche" saddle. In the Gaeta Gulf the continental shelf, supplied by clastic sediments coming from the Volturno river, is well developed. The shelf break results partially eroded in correspondence to some active canyon axes, as the Cuma canyon and to WNW of Punta Cornacchia, a canyon head located next to the Forio Bank. Along the southern Ischia offshore the continental shelf is very reduced or absent. Several sub-horizontal terraced surfaces with eroded breaks in slope in correspondence to canyon heads are localized to non-standard water depths for the volcano-tectonic movements of the island. Marine exploration of the Ischia offshore showed great improvement in the last 10 years, due to surveys carried out by the IAMC-CNR of Naples in the frame of the GNV (National Group of Volcanology) and CARG projects. These surveys resulted in a Multibeam coverage that allowed the exploration of the whole area surrounding the island (Chiocci and de Alteriis, 2006; Aiello et al., 2009a, b). The Ischia offshore is characterized by several monogenic edifices aligned along the NE-SW system of faults that connects the southeastern sector of Ischia to the island of Procida and to the Phlegrean Fields (de Alteriis and Toscano, 2003; de Alteriis et al., 2006). These edifices have been mainly formed through subaqueous explosive eruptions, documented by the hialoclastites from a potassic magma of latitebasaltic-latitic composition (Di Girolamo and Rolandi, 1976; Di Girolamo et al., 1984). Marine geophysical surveys revealed collapsed volcanic edifices located to the W and SW of the Ischia island, a sector of the seafloor characterized by strong residual magnetic anomaly fields. A westward submerged continuation of the Ischia volcanic structure, representing a remnant of the emerged top of a larger, E-W trending volcanic complex, has been also inferred, based on marine geophysical data (Bruno et al., 2002). 3. SEISMO-STRATIGRAPHIC RESULTS Here we will focus on some seismo-stratigraphic results on the southern Ischia canyon system (seismic profile L50; Fig. 2). Some geological considerations on canyons are also delineated. The canyons observed onshore are some morphological incisions controlled by a strong erosion on an underlying substratum and characterized by steep walls. As a general rule their origin is due to a sharp lowering of the erosional base level, which can be interpreted as the level of minimum potential (generally the sea level), where all the rivers converge. This realizes with a sea level lowering or a relative uplift of the mainland, for example due to the tectonics, or to isostatic adjustements of the earth's crust. The origin of the submarine canyons is similar to the terrestrial one, i.e. to a relative variation of the sea level, also if their morphology is not so harsh. Another important factor which induces the formation of canyons along the submerged continental shelves and slopes apart the sea level oscillations, is represented by a variation of the sedimentary regime due to the increase of solid supply from the rivers and the great eruptions. In the Tyrrhenian sea the main canyons have been often encountered in correspondence to tectonically active areas, such as the Calabrian Arc, which is in uplift of several hundred of meters from almost 120 ky B.P. In the Naples Bay the origin of Dohrn and Magnaghi canyon is quite different (Di Fiore et al., 2011). In fact, also if we cannot exclude a component surely linked to the tectonism (in particular for the deepest part of the Dohrn canyon), the birth of these two incisions has been mainly controlled by the volcaniclastic aggradation during the Late Pleistocene-Holocene. All the southern Procida offshore is dominated by the occurrence of the Magnaghi canyon (Aiello et al., 2001). Its trilobate head starts from the shelf break at water depths of 130-140 m. The canyon has an average width of 700-800 m, which enlarges towards the confluence up to 2 kilometres. The seismic profile L50 crosses the south-western offshore of the Ischia island, from the continental shelf, west of Punta Imperatore, to the continental slope located southward of Capo Negro (Figs. 1 and 2). The line meets three main submarine canyons (Fig. 2), pertaining to the southern Ischia canyon system. The canyons (Fig. 2) are respectively located at water depths of 173 m (canyon 1), 240 m (canyon 2) and 285 m (canyon 3). The three canyon thalwegs are bounded by levees that may evolve into extensive channel-levee complexes. A volcanic acoustic basement has also been identified (Fig. 2), dipping from the continental shelf off Punta Imperatore toward the southwestern Ischia offshore. Based on land-sea correlation, this basement could be linked to the lavas cropping out at Punta Imperatore (southwestern Ischia), represented by alkali-trachytic grey lavas, dating to about 116-123 +/- 6 ky (Vezzoli, 1988). The top of the volcanic acoustic basement appears strongly incised, probably in a subaerial environment. A wide pyroclastic edifice has been recognized, buried in the continental shelf (Fig. 2). This edifice is interstratified in the FST deposits, recognized on the continental shelf off Punta Imperatore, where Quaternary sediments are truncated by an erosional unconformity, overlain by thin highstand deposits. A relic prograding wedge has also been identified in correspondence to the western canyon, offshore southwestern Ischia, where it overlies the volcanic acoustic basement corresponding to the Punta Imperatore lavas. This wedge is overlain by a marine seismic unit, which seems to be syntectonic, since it appears to be deposited during the activity of the normal fault downthrowing the volcanic acoustic basement. REFERENCES Acocella V. and Funiciello R. (1999) The interaction between regional and local tectonics during resurgent doming: the case of island of Ischia, Italy. Journal of Volcanology and Geothermal Research, 88, 109-123. Aiello G., Budillon F., Cristofalo G., de Alteriis G., De Lauro M., Ferraro L., Marsella E., Pelosi N., Sacchi M., Tonielli R. (2001) Marine geology and morpho-bathymetry in the Bay of Naples. In: Faranda F.M., Guglielmo L., Spezie G. (Eds.) Structures and Processes of the Mediterranean Ecosystems, pp. 1-8, Springer, Italy. Aiello G., Marsella E., Passaro S. (2009a) Submarine instability processes on the continental slopes off the Campania Region (Southern Tyrrhenian sea, Italy): the case history of Ischia island (Naples Bay). Bollettino di Geofisica Teorica Applicata, 50 (2), 193-207. Aiello G., Budillon F., Conforti A., D'Argenio B., Putignano M.L., Toccaceli R.M. (2009b) Progetto per la realizzazione di cartografia geologica marina secondo le modalità CARG. Note illustrative alla cartografia geologica marina. Foglio geologico n. 464 "Ischia", Preprints, 25 May 2009, Regione Campania, Settore Geotecnica, Geotermia e Difesa Suolo, III SAL Geologia Marina, IAMC, Istituto per l'Ambiente Marino Costiero, Geomare Sud, CNR, Napoli. Aiello G., Marsella E., Passaro S. (2012) Stratigraphic and structural setting of the Ischia volcanic complex (Naples Bay, Southern Italy) revealed by submarine seismic reflection data. Rendiconti Lincei, Scienze Fisiche e Naturali, accepted article in course of printing. Bruno P.P.G., de Alteriis G., Florio G. (2002) The western undersea section of the Ischia volcanic complex (Italy, Tyrrhenian sea) inferred from marine geophysical data. Geophysical Research Letters, 29 (9):1343, doi.10.1029/2001GL013904. Catuneanu O. (2006) Principles of sequence stratigraphy. Elsevier, Amsterdam, 375 pp. Catuneanu O., Abreu V., Bhattacharya J.P., Blum M.D., Darlymple R.W., Eriksson P.G., Fielding C.R., Fisher W.L., Galloway W.E., Gibling M.R., Giles K.A., Holbrook J.M., Jordan R., Kendall C.G. St., Macurda B., Martinsen O.J., Miall A.D., Neal J.E., Nummendal D., Pomar L., Posamentier H.W., Pratt B.R., Sarg J.F., Shanley K.W., Steel R.J., Strasser A., Tucker M.E., Winker C. (2009) Towards the standardization of sequence stratigraphy. Earth Science Reviews, 92, 1-33. Chiocci F.L. and de Alteriis G. (2006) The Ischia debris avalanche: first clear submarine evidence in the Mediterranean of a volcanic island prehistorical collapse. Terra Nova 18, 202-209. Cinque A., Aucelli P.P.C., Brancaccio L., Mele R., Milia A., Robustelli G., Romano P., Russo F., Santangelo N., Sgambati D. (1997) Volcanism, tectonics and recent geomorphological change in the bay of Napoli. I.A.G. IV International Conference on Geomorphology, Geografia Fisica e Dinamica Quaternaria (Suppl. III-t.2) (1997), 123-141. de Alteriis G. and Toscano F. (2003) Introduzione alla geologia dei mari circostanti le isole flegree di Ischia, Procida e Vivara. In: Gambi M.C., De Lauro M., Iannuzzi F. (Eds.) Ambiente marino costiero e territorio delle isole flegree (Ischia, Procida e Vivara - Golfo di Napoli): Risultati di uno studio multidisciplinare, Vol. 5, Mem. Acc. Sc. Fis. e Mat. in Napoli, 3-25. de Alteriis G., Tonielli R., Passaro S., De Lauro M. (2006) Isole flegree (Ischia e Procida). Batimetria dei fondali marini della Campania. Scala 1:30.000. Liguori Editore, Napoli. Di Girolamo P. and Rolandi G. (1976) Vulcanismo sottomarino latite-basaltico latitico nel canale d'Ischia. Rendiconti Acc. Sc. Fis. e Mat. in Napoli, s.4, 42, 1-36. Di Girolamo P., Ghiara M.R., Lirer L., Munno R., Rolandi G., Stanzione D. (1984) Vulcanologia e petrologia dei Campi Flegrei. Bollettino della Società Geologica Italiana, 103, 349-370. Di Fiore V., Aiello G., D'Argenio B. (2011) Gravity instabilities in the Dohrn canyon (Bay of Naples, Southern Tyrrhenian sea): potential wave and tsunami (run-up) reconstruction from a fossil submarine landslide. Geologica Carpathica, 62 (1), 55-63. Fabbri A., Argnani A., Bortoluzzi G., Correggiari A., Gamberi F., Ligi M., Marani M., Penitenti D., Roveri M., Trincardi F. (2002) Carta geologica dei mari italiani alla scala 1:250.000. Guida al rilevamento. Presidenza del Consiglio dei Ministri, Dipartimento per i Servizi Tecnici Nazionali, Servizio Geologico, Quaderni serie III, vol. 8, pp. 1-93. Helland-Hansen W. and Gjielberg J.G. (1994) Conceptual basis and variability in sequence stratigraphy: a different perspective. Sedimentary Geology, 92., 31-52. Gillot P.Y., Chiesa S., Pasquarè G., Vezzoli L. (1982) 33.000 yr K/Ar dating of the volcano-tectonic horst of the isle of Ischia, Gulf of Naples. Nature, 229, 242-245. Posamentier H.W. and Allen G.P. (1993) Variability of the sequence stratigraphic model: effects of local basin factors. Sedimentary Geology, 86, 91-109. Posamentier H.W., Erskine R.D., Mitchum R.M. (1991) Models for submarine-fan deposition within a sequence stratigraphic framework. In. Weimer P., Link M.H. (Eds.) Seismic facies and sedimentary processes of submarine fans and turbidite systems. Springer, New York, pp. 127-136. Tibaldi A. and Vezzoli L. (1998) The space problem of caldera resurgence: an example from Ischia Island, Italy. Geological Rundschau, 87, 53-66. Trincardi F., Correggiari A., Roveri M. (1994) Late Quaternary transgressive erosion and deposition in a modern continental shelf: the Adriatic semienclosed basin. Geomarine Letters, 14, 41-51. Vezzoli L. (1988) Island of Ischia, CNR, Quaderni De La Ricerca Scientifica, Roma.