One aim of the present paper is to show the magnetic anomaly map of the Naples Bay [1] , which has furnished a new contribution to the knowledge of the geophysics and the volcanology of this active volcanic area, located at the Eastern Tyrrhenian margin, characterized by a complex geological setting, depending on the interference between volcanic and sedimentary processes during the Late Quaternary [2] - [6] .

The magnetic survey of the Naples Bay acquired by the Institute of Marine and Coastal Environment of the National Research Council of Naples (Italy) onboard of the R/V Urania (CNR) during the oceanographic cruise GMS98-01 (May-June 1998) and GMS00-05 (October-November 2000) shows a densely spaced coverage, distinguishing from the aeromagnetic surveys, previously recorded in the area and characterized by a large coverage [7] . This has allowed for the construction of a high resolution magnetic anomaly map of the Naples Bay, which has evidenced the occurrence of complex magnetic anomaly fields, previously unknown, related to geological structures having a volcanic nature and/or to volcanic morpho-structural highs, evident from the Multibeam bathymetry of the Gulf of Naples [8] [9] .

It is worth mentioning the previous lack of magnetic data in the marine sector of the Gulf of Naples, both on the aeromagnetic survey [7] and the magnetic anomaly map of Italy constructed by the National Institute of Geophysics and Volcanology (INGV, Rome, Italy) [10] . The Italian magnetic anomaly map is based on magnetic measurements collected onshore in the frame of the Project Finalized Geodynamics (National Research Council of Italy) from the 1977 to the 1981, while the marine magnetic data have been recorded by the Experimental Geophysical Observatory (OGS, Trieste, Italy) from the 1965 to the 1972.

The most important result shown by the Italian magnetic anomaly map [10] with respect to the aeromagnetic map of Italy [7] consists of a new view of the magnetic signature related to main regional tectonic structures in the frame of their geological setting. Moreover, the magnetic anomaly map of Italy has evidenced a good correlation among the structural geology (onshore) and the magnetic anomalies, allowing for a detailed interpretation of deep geological structures. The magnetic anomaly map of the Gulf of Naples, herein presented, integrates these elaborations, considering that the magnetic grid is densely spaced and that an accurate pre-processing and post-processing of the magnetic data have been performed [3] .

Advanced magnetic data processing has been applied through geophysical inversion of magnetic data, allowing the reconstruction of the shape of the magnetic anomalies [4] and their consequent geologic interpretation through an integrated analysis of magnetic, seismic and bathymetric data [5] [11] . This interpretation allows to bind the shape of the magnetic anomaly fields shown by the Naples magnetic anomaly map and to put them in relationship with the volcanic bodies occurring in the subsurface of the Gulf of Naples, identified through the analysis of multichannel seismic reflection profiles recorded on the same navigation lines of magnetic data [2] [12] . At the same time, the magnetic anomalies individuated in different magnetic fields will be correlated with the bathymetry of the Naples Bay, reconstructed through the analysis of single-beam bathymetric profiles, recorded on the same navigation lines of magnetometric and seismic data. A first example of this integrated analysis of magnetic, seismic and bathymetric data, applied to a wide dipolar anomaly, located in the offshore of the Somma-Vesuvius volcanic complex and probably correlated with a lateral vent of the volcano developed on the continental shelf surrounding the Torre del Greco town has been reported by [12] .

The boundary analysis is a numerical methodology allowing for the localization of the lateral margins bounding the body which is the source of the anomaly. The applied techniques are based on the signal enhancement. The most used methods are represented by the analytic signal and the horizontal derivative of the magnetic field. Both the methods are based on the assumption that the contrasts between the source body and the enclosing rocks are abrupt and almost vertical. The analytic signal is a complex function composed of the horizontal and vertical components of the potential field. The width of the analytic signal is a bell-shaped function localized over the margin of the structure. A margin of the source body generally corresponds to a maximum of amplitude of the signal. This technique is not depending on the direction of the vector of magnetization and of the vector of the earth’s magnetic field, more than on the variation in shape of the anomaly with the latitude [13] .

In order to solve the reverse problem of the interpretation of the fields of potential, which does not allow the determination of the distribution of the sources which have produced the field, a new methodology called the wavelet analysis has been introduced [14] . This technique may be used for the separation of the regional field from the residual one, in order to discriminate the effects of different sources which are superimposed in one single anomaly, but also to eliminate the effects of the noise remaining after the magnetic data leveling.

The Continuous Wavelet Transform (CWT) [14] [15] allows for the fractionation of the signal in a space- scale domain and is particularly indicated in order to visualize the singularity of the signal. The graph furnishes a representation of the characteristics of the field derivatives, which are prolonged at different heights. In particular, the lines of the Wavelet coefficient of a maximum amplitude, in the case of isolated sources, are straight lines joining up the source depth. In the case of wide sources represented by homogeneous bodies having a regular vertical section the field potential depends on the coordinates of the source vertexes. Correct information may be obtained through a proper selection of the scale range, whose vertexes act as isolated singularities. The Wavelet transform is then a feasible technique to study not stationary signals, in which there is the superimposition of high and low frequency signals [14] [15] .

The area involved by the present study includes the Gulf of Naples, a sedimentary basin located on the Eastern Tyrrhenian margin and characterized by high rates of subsidence during the Late Quaternary, as a result of volcano-tectonic downthrowing of the area. Main volcanic events have involved this area during this time interval, controlling the emplacement of volcanic bodies widespread in the subsurface of the gulf (see for instance the seismic unit related with the pyroclastic flux deposits of the Campanian Ignimbrite, erupted by the Phlegrean volcanic complex at 37 ky B.P. [16] ).

The basin fill of the Gulf of Naples has recorded the interactions between tectonic, volcanic and depositional/erosional processes, together with the tectonic uplift and the deformation of the surrounding emerged areas during the Pleistocene. Particular aspects of the Gulf of Naples with respect to adjacent peri-tyrrhenian basins (i.e. the Terracina and Gaeta basins to the north and the Policastro basin to the south) is due both to the occurrence of a structural high of the Mesozoic carbonate basement (Sorrento Peninsula-Capri island structural high), playing a fundamental role in the individuation and recent tectonic evolution of the basin itself, and on the strong volcanic activity during the Late Pleistocene (volcanic complexes of Phlegrean Fields, Somma-Vesuvius and Ischia and Procida islands), controlling a notable complexity in the distribution of the sedimentary and volcanic seismic units. The western sector of the Naples Bay is characterized by the occurrence of volcanic seismic units, often associated with positive magnetic anomalies, while the eastern one is characterized by the occurrence of sedimentary units [17] .

The survey area, in which the coverage of magnetic data used to construct the magnetic map is located, is bounded towards the Vesuvian coast by the 50 m isobaths; towards the Sorrento Peninsula-Capri island prolongation the lower bathymetric boundary ranges between the 100 m isobaths (towards Capri-Punta Campanella) and the 70 m isobaths (towards the inner sector of the Sorrento Peninsula). Towards the shoreline of the Naples town, where the continental shelf strongly widens, the bathymetric boundary coincides with the 30 m isobath; towards the Gulf of Pozzuoli it coincides with the 70 m isobath. Offshore the Ischia and Procida islands the boundary of the survey area coincides with the 100 m isobaths. Proceeding towards the centre of the gulf, in correspondence with the continental slope of the Naples Gulf, the magnetic data have been recorded with a dense line spacing of 250 m since the 300 m isobaths, in correspondence to the Dohrn canyon’s head. The remaining part of the continental slope of the gulf has been covered by a larger grid (line spacing of 2.5 km). At the same time, the area surrounding the Ischia and Procida islands is covered by a densely spaced grid among the 100 and 400 m isobaths.

The survey operations at sea have been carried out during two oceanographic cruises, both developed onboard of the R/V Urania of the National Research Council.

During the first cruise (GMS98-01; May-June 1998) the magnetic surveys have been performed during the night contemporaneously with the recording of single-channel seismic profiles (Sparker 1 kJ and 4 kJ). The oceanographic cruise, performed in the frame of the CARG research project of realization and informatization of thematic geologic maps at the 1:50.000 scale of Naples and Salerno Gulfs, had as a main scientific objective the realization of sea bottom sampling and of geophysical prospecting in the Naples and Salerno Gulfs [18] . The line spacing of the magnetic grid recorded during the GMS98-01 cruise corresponds to 2.5 kilometers (Figure 1).

During the second oceanographic cruise (GMS00-05; October-November 2000) 950 kilometers of magnetic profiles have been recorded, coupled with a grid of seismoacoustic profiles (Figure 2).

Single-beam bathymetric profiles have also been collected along the same navigation lines of seismic profiles. This grid has allowed for the construction of the magnetic anomaly map of the Naples Bay, due to the fact that it is densely spaced and to the accuracy of the used positioning (GPS differential positioning in dotation to the R/V Urania).

The calendar of the work activities carried out during the second cruise is reported in Table 1. The coordinates of the seismic and magnetic lines recorded in the cruise GMS00-05 (see Figure 2 for location) are shown in Table 2.

The continental shelf between the Gaeta Gulf and the Cilento Promontory represents the seaward extension of the alluvial coastal plains bounding the Tyrrhenian sector of the Apenninic chain, which have individuated after strong rates of tectonic subsidence in a tectonic regime of continental stretching and extension. These alluvial plains (Campania plain, Sarno plain and Sele plain) are bounded towards north-east by the inner reliefs of the Apenninic chain, whose continuity is interrupted by NE-SW trending structural highs and by volcanic complexes (Phlegrean Fields and Somma-Vesuvius). The sedimentary filling consists of marine clastic and continental sediments, alternating, both in the Campania Plain and in the Sarno Plain, with abundant volcanic products. The age of this filling is mainly Pleistocene, although a precise dating of the first sequences overlying the acoustic basement is lacking [23] . The acoustic basement is represented by Meso-Cenozoic carbonates (Campania-Lucania carbonate platform) [24] and by deformed Cenozoic sequences and related flysch deposits (“Cilento Flysch”, “Sicilide Units” and “Liguride Units”) [25] . The southern boundary of the Campania Plain is repre- sented by the volcanic district of the Phlegrean Fields, which has been active during the last 50 ky [26] .

The reliefs bounding the Campania Plain are composed of carbonate rocks (limestones and dolomites ranging in age from the Late Triassic and the Late Cretaceous), organized as tectonic units emplaced during the Late Miocene. Remnants of Miocene siliciclastic units often occur at the top of the upper carbonate units. Under the tectonic depression of the Campania Plain the aforementioned units have been deeply buried under the Quaternary deposits, reaching a maximum depth of 3.5 kilometres. Next to the Volturno river mouth, marine sediments not older than the Emilian (1.45 - 1.15 My) have been drilled up to a depth of 3 kilometers [27] . Based on these data a qualitative estimation of the subsidence rates in the Campania plain during the Quaternary has given average values ranging between 1.2 and 3 m/ky [28] .

During the Late Pliocene-Early Pleistocene important phases of uplift and block-faulting have characterized the carbonate reliefs bounding the Campania plain. After these phases, some sectors have ended their uplift and the bottom valley has been filled by thick alluvial and lacustrine deposits (i.e. Volturno valley and Solofrana valley). Some sectors, instead, continued to uplift, also if with minor rates, during the Middle Pleistocene (Caserta, Nola and Sarno Mounts; Sorrento Peninsula). Starting from the last interglacial, a tectonic stability has characterized the structural highs bounding the Campania Plain. The latter one continued to downthrow, due to the high rates of subsidence, also during the Late Quaternary, such that the whole Campania plain has been flooded by the sea during the late interglacial highstand. In fact, beach deposits, having a Tyrrhenian age, have been drilled also at the base of the mountains bounding the plain towards north-east [28] . The first regressive peak of the last interglacial has produced an advance of the shoreline towards north-east of about 30 kilometers, about in the present-day location of the continental platform margin. The effect of this emersion has been reinforced by the growth of the first volcanic edifices in the Neapolitan area and by the consequent pyroclastic aggradation of the surrounding plain.

The origin of the sedimentary basins and their subsidence along the Campania sector of the Eastern Tyrrhenian margin have been the object of several studies based on geological observation in the field and on seismic and well data in the subsurface, both onshore and offshore [24] [27] [29] - [35] .

Nonetheless this, the relative scarcity of recent seismic data and the lack of lithostratigraphic data of deep wells in the Naples Bay has make difficult the reconstruction of the basin age formation and the calibration, also if qualitative, of the seismic sequences.

The Naples Bay has been surveyed through several surveys of seismic reflection data, mainly single-channel seismic recorded with a Sparker seismic source by the Institute of Oceanology of the Naval University Institute of Naples, Italy [17] [36] - [39] . Seven seismic sedimentary units, ranging in age from the Mesozoic and the Holocene have been recognized [17] . The oldest ones have been identified as Mesozoic carbonates and Miocene flysch, separated from the Plio-Quaternary units by an erosional truncation. Some volcanic units have also been described, aligned along a tectonic lineament having a N10˚ trending, following the Dohrn canyon trend and dividing the Naples Bay in a sedimentary domain to the east and a volcanic domain to the west.

The continental shelf of the Naples Bay has a variable width, ranging between 2.5 kilometers (offshore the western sector of the Capri island) and 10 - 15 kilometers (offshore the Sorrento coastline). Such a physiography has been controlled by the interactions among subaerial and submarine volcanism, strongly involving the Gulf of Naples during the Late Pleistocene and the linear erosion controlled by Dohrn and Magnaghi canyons and by their tributary channels. The most part of the continental shelf of the Naples Bay is draped by Holocene sediments relative to the last highstand of the sea level.

The western sector of the Gulf of Naples is characterized by the occurrence of several volcanic banks, related to positive magnetic anomalies [40] [41] . Some of them are located in the continental shelf (Pentapalummo, Nisida and Miseno banks; Carenella bank); other ones are located at the beginning of the slope sector (Gaia bank and three minor banks located westwards of the latter one). Some relicts of submarine volcanic complexes occur among the Ischia and Procida islands (Formiche di Vivara, La Catena and Ischia banks). These banks represent relicts volcanic morphologies. Some of them are almost completely eroded and characterized by the outcropping, at the sea bottom, under a thin drape of Holocene sediments, of polycyclic erosional surfaces eroded in the volcanic deposits (Pentapalummo and Ischia banks) or by a thicker Holocene sedimentation (Nisida and Miseno banks).

At the center of the Gulf of Naples, between the Ischia and Procida islands a structural high having a sedimentary nature occurs, prolonged in a NE-SW direction (Banco di Fuori or Banco di Bocca Grande), not related to significant magnetic anomalies [5] . The Banco di Fuori reaches at its top the minimum depth of 130 m and is covered by more than 100 msec of Holocene sediments. It is represented by an asymmetrical ridge, with the south-eastern flank higher than the north-western one. It is represented by a main morpho-structural high, presumably formed by a tilted block of Mesozoic carbonates, resulting from the uplift and the rotation, at a regional scale, of the carbonate acoustic basement. This is located on the structural prolongation Capri-Sorrento Peninsula and its southern flank seems to be involved by a normal fault having a N10˚ trending [42] .

Among the continental slope and the morpho-structural high of Banco di Fuori a basinal area having a low gradient occurs, at water depths ranging between 300 and 500 meters, constituting a slope basin located at the mouth of the Ammontatura channel.

The erosion and the transport of sediments in the Gulf of Naples have acted along the main axes of the Dohrn and Magnaghi canyons, located on the continental shelf and slope and exposing along their walls some hundred of meters of a prograding wedge of the Middle-Late Pleistocene, formed by clastic and volcaniclastic sediments. The canyon’s width ranges between a few hundred of meters and more than one kilometer. Their depth ranges between 250 meters at the shelf break to 1300 meters joining up the bathyal plain. The gradients of their walls reach more than 35˚ in the steepest sectors.

The Dohrn canyon, draining the whole Gulf of Naples, is characterized by two main branches having a curved planimetry. The northern branch joins up the continental shelf through a wide channel (about 2.5 kilometers) and deep from 20 to 40 meters (Ammontatura channel), characterized by a flat bottom and asymmetrical levees. In its terminal part the Ammontatura channel, distinguished by a curved shape in planimetry, deviates towards NW and sharply ends in correspondence to the Nisida bank. The southern branch, having a E-W trending, is fed by a dense network of tributary channels, ending some kilometers to the west of the shelf break, located at water depths of 135 - 140 meters.

The erosion and the transport of volcaniclastic sediments in the offshore of Ischia and Procida islands have acted along the Magnaghi canyon’s axis, which does not seem linked to an onshore drainage system, old or recent. The Magnaghi canyon’s heads is typically trilobate and is typically imposed on a retreating platform margin, having three tributary channels joining into the basin with a main axis. In the zones surrounding the canyon several areas having submarine instabilities occur, as shown by the occurrence of active erosional phases on the continental slope towards the south-east of the Procida island. The origin of the Magnaghi canyon is presumably linked with the great volcaniclastic supplies during several phases of volcanic activity in the Ischia and Procida islands [43] [44] .

Northwards to the area of the volcanic banks the depression of the Gulf of Pozzuoli occurs [45] , characterized by a coastal platform whose rim, located at water depths of 50 m, passes through a low angle slope to a central basin developed to about 100 meters of water depth and surrounded seawards by the Phlegrean volcanic banks. Several authors are concord to retain that the Gulf of Pozzuoli, characterized by high rates of subsidence during the Holocene and volcano-tectonic uplifts dated back to about 5 - 6 ky B.P. (marine terrace of La Starza) represents a submerged sector of the Phlegrean caldera [38] [46] - [48] , also in the light of studies on bradyseismic movements [49] - [51] .

Main seismic facies identified in the Naples basin based on the interpretation of seismic profiles and their characteristics are resumed in Table 4. Five main unconformities have been distinguished, separating the seismic units and delineating the tectono-sedimentary evolution of the basin.

The acoustic basement is represented by Meso-Cenozoic platform carbonates (seismic unit 1 in Table 4), widely cropping out in the Sorrento Peninsula and in the Capri island, organized as a monoclinalic structure dipping towards NW. The measured inclination of the seismic reflectors in the carbonate sequence is of about 6˚ - 7˚; these values are similar to those ones shown in outcrop from Mesozoic carbonates of the Sorrento Peninsula [42] [52] [53] .

The Naples basin filling mainly consists of two main sedimentary wedges, each characterized by particular patterns of the reflections and acoustic facies. The dating of the seismic sequences in the Naples basin is tentative, since deep offshore wells have not been drilled. An indirect calibration may be attempted based on the data of the geothermal well “Trecase 1” [54] , only for the Vesuvius offshore.

The geothermal well “Trecase 1” has been drilled between the 1980 and the 1981 at a height of 220 m on the southern slopes of the volcanic vents of Somma-Vesuvius [54] [55] for an overall depth of 2068 meters. The Trecase 1 well has drilled the subaerial lavas and the pyroclastic products having an age younger than 35 ky B.P. at the Somma-Vesuvius (0 - 252 m), overlying alternating pumiceus products, cineritic products, breccias and volcanic sands (252 - 510 m), genetically related with the volcanic activity of the Phlegrean Fields (Campanian Ignimbrite; 37 ky B.P.) [56] . A Pleistocene volcano-sedimentary succession composed of submarine volcanites of the old Somma volcano with marine sediments has been crossed since 1490 meters of depth. The top of the carbonate acoustic basement has been detected at a depth of 1885 m, testifying a strong downthrowing of Mesozoic platform carbonates in the Somma-Vesuvius area. The lithostratigraphic data of the Trecase 1 well fully confirmed the structure of the basement of the Somma-Vesuvius deduced from geophysical surveys [57] , indicating strong rates of subsidence of the Campania plain starting from one million of years ago. The alternance of basic lavas and pyroclastic products in drilled eruptive sequence suggests the occurrence of several eruptive cycles in the Somma-Vesuvius history [58] .

In the Torre del Greco offshore a large and delineated anomaly occurs (Figure 9), genetically related with the

eruptive activity, during recent times, of the Somma-Vesuvius volcanic complex. The correlation of seismic and magnetic profiles has been carried out by [5] . The profile GR09 runs parallel to the shoreline from Torre del Greco to the Sorrento Peninsula crossing the Sarno plain. It is located in the inner continental shelf, where the water depths are less than 100 meters (Figure 9); the negative consequence for the seismic acquisition is a not excellent penetration of the source signal and a restitution of the profile showing some multiples. By analyzing the track of the line it is possible to see that the first seismic unit is characterized by parallel and continuous seismic reflectors, interpreted as coastal and marine sediments, deposited by the Sarno river, ranging in age between the Late Pleistocene and the Holocene. The sediments overlie an acoustically-transparent volcanic unit, characterized by a flat lower boundary, while the upper boundary is strongly irregular and describes the upper parts of dome-shaped volcanic structures. The latter unit which has been recognized, occurring only in the part to the south-east of this seismic profile, has been interpreted as the pyroclastic flux deposits of the Campanian Ignimbrite [43] . The Campanian Ignimbrite is a stratigraphic unit widely cropping out in the Sorrento Peninsula and recognized in seismic profiles as sub-outcropping in the eastern sector of the Gulf of Naples. The dome- shaped structures deforming the Ignimbrite are interpreted as submerged and/or buried lateral vents, correlated with the Somma-Vesuvius volcanic complex [63] .

The widest one extends for about 7.5 kilometers offshore the Torre del Greco town. Its upper part shows three main peaks (shot points 600 - 1300), aligned along a system of normal faults, having a NNW-SSE trending, correlated with the maximum values of anomalies singled out by the magnetic profile. The detailed magnetic anomaly field may be observed in Figure 9, characterized by three main peaks. Two of them have a dipolar shape, while for the central peak it has been recognized only a maximum value about +350 nT. The values found for the anomaly located northwards are a maximum of +350 nT related to a minimum of −160 nT. The magnetic dipole located southwards shows minor absolute values, with a maximum of about +160 nT related to a minimum of −120 nT. The thickness of the unit recognized as the Campanian Ignimbrite is of about one hundred meters based on previously described seismic profiles [5] [11] is comparable with the thickness encountered by the Trecase 1 well [54] . During the deposition the unit has probably overlain an inclined palaeomorphology, as evidenced by the landwards immersion of the erosional unit located to its base or alternatively, the unit has been involved by a tectonic deformation of the continental shelf. In proximity to the present-day shelf break, in the central sector of the gulf, some relicts morphological highs occur. The correlation between the seismic and magnetic profiles confirms the volcanic nature of the dome-shaped structure, deforming the Campanian Ignimbrite unit [5] [11] . The maximum variation of the magnetic anomaly is of about 120 nT. The trending of the anomalies and related seismic structures, about NNW-SSE, suggests that such a structural trend in the Vesuvius offshore occurs, differently to that suggested by previous authors, suggesting systems of normal faults, having a NE-SW trending [37] [46] [57] [64] [65] .

Previously interpreted seismic profiles [5] [11] have allowed for the investigation of the magnetic anomaly field named as 2, whose detail is shown in Figure 10. It is composed of a set of minor anomalies, aligned according to a E-W direction. These anomalies do not occur in a dipolar shape and form a succession of magnetic maxima having values in the order of hundreds of nanotesla. They are genetically related with buried edifices in the zone of the Nisida bank and related tuff cones. The interpretation of the magnetic anomaly map suggests a possible localization of the submerged margin of the Phlegrean caldera in this area.

Several dipoles have been noted in the detailed magnetic anomaly map offshore the Phlegrean Fields volcanic complex (Figure 11). Two of them are the most important ones. The first one is located in the upper part of the survey area and is characterized by a minimum of −200 nT, related to a maximum of +185 nT, having a E-W trending. The second one, oriented in a NW-SE direction, occurs in the eastern part of the involved area and shows magnetization values having the same order of the previously mentioned ones. Interpreted seismic sections have shown the stratigraphic architecture of this area, characterized by the occurrence of volcanic and sedimentary seismic units. Detailed magnetic anomaly map of the Ischia bank is also reported in Figure 12, shown here for its similarity with aforementioned volcanic banks.

The magnetic anomaly field singled out as 5 (Figure 12) is related with the submarine volcanic bank, namely Gaia, located next to the shelf break on the isobath of 140 m. It shows a maximum of +170 nT, which puts in evidence a high magnetic susceptibility of the structure. There is a discrete correlation among the shape of the magnetic anomaly and the sea bottom morphology.

In correspondence to the Magnaghi canyon’s head, shown as the magnetic anomaly field (Figure 13) a magnetic anomaly, not dipolar and characterized by a maximum of +170 nT, occurs, significantly eroding the volcanic deposits of the Procida slope. This confirms that the Magnaghi canyon is completely incised in volcanic deposits, as evidenced both by the occurrence of magnetic anomalies both at the branch and in the canyon’s axis. On the contrary, the Dohrn canyon, characterized by two branches merging into an axis arriving up to 1000 m of depth, does not show significant magnetic anomalies, confirming that it erodes sedimentary units supplied by the paleo-Sarno river mouth. Stratigraphic data on the Naples Bay canyons have been deeply analyzed in previous papers [9] [21] [61] .

Another important anomaly, circular in shape, has been identified on the continental slope of the gulf (Figure 14) in the sector among the two canyons. It occurs as a single maximum around the +145 nT, indicated as the magnetic anomaly field n. 7. It may suggest the occurrence of a previously unknown volcanic edifice on the flank of the Dohrn canyon.

A main morpho-structural high has been crossed by the profile (Banco di Fuori or Banco di Bocca Grande), which separates the Dohrn canyon from the Magnaghi canyon and is presumably composed of blocks of Mesozoic carbonates resulting from the uplift and the regional inclination of the carbonate acoustic basement [8] . The bank is overlain by Late Pleistocene-Holocene sediments and its southern flank is steeper than the northern one, suggesting the occurrence of a normal fault. The Magnaghi canyon’s axis is characterized by the occurrence of a magnetic magnetic anomaly field indicated as 10 (Figure 15). The anomaly shows a dipolar shape, with a maximum value around the +110 nT related to a minimum of −50 nT, with a trending of the minimum-maxi- mum trending from SSW to NNE.