Search

Starting with the tragic case of the earthquake in L'Aquila this paper discusses a fundamental aspect of the correct evaluation of the danger (hazard) of an area and of a specific urban site, that is, the underestimation of the amplyfying effect of the sites in many developed Italian urgan areas situated in valleys or alluvial plains along with a scarce or incomplete knowledge of the geoseismic parameters of the local underground area.

In this paper we give an overview of the recent geophysical, geochemical and volcanological studies concerning the island of Ischia within the geological and tectonic framework of Southern Italy. Ischia is an active volcanic field that had a complex volcanic history resulting from dominant explosive and minor effusive activity, several caldera collapses, and renewed volcanism from vents located inside the collapsed area. The island is morphologically dominated by Mt. Epomeo, the result of a prominent resurgence phenomenon taking place since ca. 33 ka BP, and responsible for ca. 900 m of total uplift, one of the largest known compared to the relatively small size of the caldera. The uplift was accompanied by activation of faults, seismic activity and renewal of volcanism, and may be considered a main factor for inducing slope instability. For Ischia, volcanological, petrological and geophysical studies are, at present, limited compared to the other active volcanoes of the Neapolitan Area. Furthermore, the island is characterized by high volcanic, seismic and hydrogeological risks. Thus, this review is aimed at highlighting aspects of the knowledge on Ischia that need more investigations, in order to better assess some characteristics of its structural setting. Features such as the precise location of the caldera boundaries and the depth of the magma chamber representing the drive for the resurgence still need to be well defined. A critical analysis of all lines of evidence relevant to the current theories about the island resurgence ( resurgent block vs. resurgent dome ) has been carried out. Our analysis reveals that the resurgent block model, differently from the resurgent dome model, is consistent with the most significant features, such as tilting of the resurgent block, faults type, dip and distribution at the edges of the block, and occurrence of most of the past 10 ka eruption vents on the eastern sector of the island. However, as both model require an input of fresh magma into the shallow plumbing system, it is not clear at present how much magma was necessary to achieve the measured uplift, and whether the drive was provided by magma or magmatic volatiles.

In this paper we present an approach for evaluating landslide susceptibility in seismic areas. It is known that earthquake-induced landslide susceptibility is related to several, often interplaying, factors. Nevertheless, an effective grade-2 zonation should be characterized by a good balance between simplicity, quickness and reliability. The GIS-based procedure we present employs only three factors that we believe are the most significant in this susceptibility assessment: the type of outcropping rocks/soils, the slope angle and the MCS intensity. The local annual precipitation, certainly an essential factor, is considered here as a parameter whose seasonal pattern is constant in time and space. Each of the three parameters is expressed as a Significance percentage and the resulting Seismic Landslide Susceptibility level of an area is given by the average of the significances of the first two factors multiplied by the significance of the third factor. The procedure was set and tested on the volcanic island of Ischia (southern Italy), which was affected by several historical earthquake-induced landslides. The results of this susceptibility zonation test at Ischia show a very good match between the distribution of the sources of historical landslides and the areas we identified as the most susceptible ones.

A complex aeromagnetic anomaly in Southern Apennines (Italy) is analysed and interpreted by a multiscale method based on the scaling function. We use multiscale methods allowing analysis of a potential field along ridges, which are lines defined by the position of the extrema of the field at the considered scales. The method developed and applied in this paper is based on the study of the scaling function of the total magnetic field. It allows recovering of source parameters such as depth and structural index. The studied area includes a Pleistocene volcanic structure (Mt. Vulture) whose intense dipolar anomaly is superimposed on a longer wavelength regional anomaly. The interpretation of ridges of the modulus of the analytic signal at different altitude ranges allows recognition of at least three distinct sources between about 5 km and 20 km depth. Their interpretation is discussed in light of borehole data and other geophysical constraints. A reasonable geological model for these sources indicates the presence of intrusions, probably linked to the past activity of Mt. Vulture.

A gravity investigation was carried out in the Somma–Vesuvius complex area (Campania, Italy) based on a dataset recently enlarged with new measurements. These cover the volcanic top and fill some other important spatial gaps in previous surveys. Besides the new gravity map of the Vesuvius, we also present the results of a 3D inverse modelling, carried out by using constraints from deep well exploration and seismic reflection surveys. The resulting density model provides a complete reconstruction of the top of the carbonate basement. This is relevant mostly on the western side of the survey area, where no significant information was previously available. Other new information regards the Somma–Vesuvius structure. It consists of an annular volume of rocks around the volcanic vent and that extends down to the carbonate basement. It results to be denser with respect to the surrounding sedimentary cover of the Campanian Plain and to the material located just along the central axis of the volcanic structure. The coherence between these features and other geophysical evidences from previous studies, will be discussed together with the other results of this research.

Several bidimensional seismic tomography surveys were carried out in urban areas of the Campi Flegrei and Somma-Vesuvius volcanic districts, Naples, Italy, with the aim of investigating the shallow subsurface and of detecting small-scale variation and heterogeneities within pyroclastic deposits. The method employed in this study is turning ray tomography (TRT). With accurate field acquisition and travel time picking and correct choice of inversion parameters, it was possible to obtain detailed P-wave tomographic models in areas characterized by thick beds of pyroclastic deposits. We were able to identify zones with heterogeneous P-wave velocities caused by the presence of buried paleochannels, or by differential welding and zeolitization in the subsurface of the investigated areas. TRT appears to be a suitable method to investigate deposits for engineering applications, at sites where the bedrock is too deep to be reached by foundations and the overburden is characterized by much heterogeneity. © 2002 Elsevier Science B.V. All rights reserved.

In this paper we describe the application of GPR and resistivity (dipole-dipole) methods to an archeological investigation. The aim of this study was to obtain information about buried pre-Roman structures below the Roman residence “Casa dell’Atrio a Mosaico,” in the ancient town of Ercolano (Naples). A number of resistivity (dipole-dipole) and GPR profiles were carried out on the mosaic floor of the house. To perform resistivity profiles in a nondestructive way on the mosaic floor, special flat-base copper electrodes were used. The electrode spacing used was [Formula: see text] and [Formula: see text]. GPR data were collected using [Formula: see text] and [Formula: see text] antennas. The radar profiles were carried out primarily along the electrical profiles in order to obtain a direct comparison between the two methods. Both resistivity and GPR methods evidenced a number of structures buried at shallow depths. Both methods located a structure identified as a conductive body with electric parameters strongly contrasting those of the surrounding material. The archaeological interpretation of such structures is in terms of remnants of walls of pre-Roman houses and of a cistern used for collecting rain, connected to a pipe.

Eleven seismic reflection lines recorded by the Italian Petroleum Agency, Azienda Generale Italiana Petroli (AGIP), in 1982–1984 around the flanks of the Somma-Vesuvius complex were utilized for studying its sub-surface structure. A new seismic reflection profile acquired within the Avellino caldera, at the southwestern edge of the Great Cone of Vesuvius, integrates the AGIP seismic dataset. The new reflection profile allows us to delineate two main reflectors. The first reflector may indicate a SW lateral collapse experienced by the volcano, probably between 35 and 11 ka ago. Evidence of this seismic discontinuity was also found on one AGIP line and on some refraction surveys. Other volcanic structures, such as buried adventive craters, dikes and pyroclastic deposits were detected on the eastern side of the volcanic complex. In particular, two shallow undulated reflectors are interpreted as pyroclastic deposits older than the Campanian Ignimbrite (CI). The study confirmed the presence of NW–SE striking faults crosscutting Vesuvius, which probably played a major role in the genesis of the volcano. Finally, evidence of ring faults was found mainly in the northeastern and southeastern sectors of the volcano. These faults yielded a low signal-to-noise area characterized by high lateral heterogeneity and the presence of a large number of fractures, possibly due to the stress field created by collapse of the volcanic structure.

Numerous methods have been used for upward continuation, but most of them require data on a regular grid. Gridding can introduce errors that affect the continued data in an unpredictable way. To avoid this problem, we design a continuation operator used for the direct continuation of scattered data on a 3-D basis. In this approach a harmonic function, satisfying the constraints imposed by the measured data, is developed. The continuation is written in the form of a linear combination of the measured data, but it depends on the arbitrary choice of the topographic zero level. However, the coefficients of the linear combination depend only on the position of the data points. This allows the zero level to be estimated on the basis of the continuation of synthetic anomalies calculated between the starting and ending surface. An important feature of the method is its local character, which allows the reduction of computation time. Also, the stability of the method for noisy data is reasonably good. The method is applied to both synthetic and real cases. Synthetic examples show how gridding‐related errors may affect the continuation when an irregular distribution of data points and a variable topography are considered.

The observed Bouguer gravity anomalies of Egypt and surrounding areas have been analysed in terms of the gravity field components due to the lower crust-upper mantle interface (Moho). Band-pass filtering of the observed field in the wavelength band 300 < Λ < 700 km has been assumed to be related to the variable crustal thickness of the area. Seven gravity profiles were chosen and interpreted in terms of 2.51) models. These profiles were constrained by structural sections based on previous seismic survey interpretations from the northern Red Sea and adjoining continental crust. A mean density of 3.30 g cm−3 was used for the upper mantle and a density of 2.90 g cm−3 was given to the lower crust. The density of the mantle upwelling assumed for the Red Sea area was 3.15 g cm−3. The result of the 2.5D gravity modelling allowed the construction of a map showing the depth variation of the interface between the upper mantle and the lower crust of Egypt.

The main objective of the present study is to evaluate seismic attenuation relationships for the Campanian area (southern Italy) using the felt intensity report data obtained from comprehensive historical databases (DOM 4.1). We focused our attention on the Campania region because it is characterized by a high seismic hazard and risk, particularly in the Naples area and its suburbs. In order to derive an attenuation relationship for the area, we fitted the observed data by using several functions. We found that a linear plus logarithmic model gives the best fits for the data in the Campanian region. Most of the attenuation relationships proposed up to now for the Italian Peninsula have an isotropic behavior and do not always properly describe the macroseismic attenuation. Therefore, in order to check the possible dependence of the attenuation on the azimuth of the seismic rays, we divided our data set in octants and performed for each of them the same analysis we carried out for the whole data set. The obtained results differ from octant to octant and the differences, besides being associated with the source effects, could be interpreted as probably due to the existence of lateral variations in the lithological and physical features of the crust at different depths, which could affect the patterns of attenuation.

In this paper we recall a method for medium scale (level-2) zoning of seismic-induced landslide susceptibility and present its application to the Sannio-Irpinia area, Southern Italy. Previous small scale studies of the entire Campania Region identified this area as one of the most susceptible to earthquake-induced landslides in the region. The area's intense seismic and landslide activity and the characteristics of the deposits involved in landslides make this analysis an interesting case study for land planning, management and protection of an area characterized by high seismic and hydrogeological hazard. The result of the zoning shows good agreement between the distribution of the historical earthquake-triggered landslides and the areas defined by the method as the most susceptible ones. They also highlight the method's effectiveness in the presence of complex clayey deposits. (C) 2013 Elsevier Ltd. All rights reserved.

Gravity data have been used to examine the crystalline basement morphology along five geotransects in Somalia defined by the Global Geotransect Project (Monger 1989). The gravity data were digitized from the 1:1 000 000 Gravity Anomaly Map of Somalia produced by the African Gravity Project. After the removal of the non-crustal wavelength anomalies from the observed gravity field, the remaining gravity anomalies were interpreted in terms of 2.5D crustal models. Available geophysical and well data, and other geological information, were used as constraints for the construction of the crustal sections. Mean densities varying from 3.30 to 3.15 g cm −3 were used for dense bodies observed on the lower continental crust of the southern Somali basins. A density of 3.00 g cm −3 was given to the oceanic crust offshore. The density of the crystalline basement and the overlying sediments were, respectively, assumed to be 2.85 g cm −3 and 2.46 g cm −3 . Coherent and incoherent marine sediments were given densities varying from 1.70 g cm −3 to 2.30 g cm −3 . The results of the 2.5D gravity modelling indicate that the basement beneath the southern Somali basins is partially or totally transformed to denser material and that, just a few hundred kilometres offshore from Somalia, the basement is of an oceanic nature.

We will be deliberately short in this reply. In fact, since the interest obtained by our work on potential-field depth resolution, we are writing new papers to give further insights into the theory. Let us begin with the discussion by Oldenburg and Li. We agree that our points of view are still distant, but it is surprising for us to realize that the crucial example that they use to manifest their opinions is completely wrong. To be clear, we refer to their main criticism above the multilevel data inversion, “We believe the authors erred when trying to extend the 1D result to general 3D cases.” Oldenburg and Li substantiate this opinion by showing a section of an inverted 3D model (their Figure 2 at right, the source space is subdivided into 1960 cells, each size 125 m by 100 m by 300 m), which, “does not show any resemblance to the true model.” To this end, they further argue that, “Although results are not reproduced here for brevity, numerical experiments have shown that including additional levels of data in the unconstrained 3D inversion does not improve the result either.” FIG. 2. (a) The central vertical section of the same 3D body as in Figure 1 but after inversion of multilevel data sets consisting of 196 data points/level for ten levels, from 0 to 0.8 km height. (b) 196 data points/level for eight levels from 0 to 0.8 km height. Differently from what is supposed in the discussion by Oldenburg and Li (this issue), the depth resolution is also obtained when the data number is not greater than the number of unknowns. We do not know the number and the type of such numerical experiments, but our numerical experiment (Figure 1), reproducible by …

Following the April 6 2009 L'Aquila earthquake, a great effort has been carried out by numerous research institutions for seismic microzonation purposes of urban areas in order to evaluate the seismic potential of the main active faults of the epicentral area. This is the case of the active Mt. Pettino master extensional fault (hereafter PEF) which controls the tectono-sedimentary evolution of western L'Aquila Basin. PEF is near to a strongly urbanized area which coincides with its pediment. This condition shows a high seismic exposition, so that specifically devoted multidisciplinary investigations, organised in subsequent in-depth steps and whose results are presented here, permitted to fine-tune its seismic hazard evaluation. The investigations were mainly based on a seismic reflection profile orthogonal to the fault strike in its hangingwall. The seismic profile was interpreted by comparison with the geological outcropping data and the stratigraphic analysis of numerous boreholes, several of which reached the pre-Quaternary substratum. The main goals were double: (i) to improve the integrated geological-geophysical subsurface model for the evaluation of the local seismic amplification and (ii) to estimate the PEF seismic hazard through the study of the sedimentary infill evolution and the tectonic subsidence of the PEF hangingwall which were strictly interrelated with the PEF seismic history.

In this paper, we present a GIS-based method for regional zoning of seismic-induced landslide susceptibility and show its application to the territory of the Campania region, Southern Italy. The method employs only three factors that we believe are most significant in the susceptibility assessment: the type of outcropping rock/soil, the slope angle, and the MCS intensity. Each of the three parameters is quantified in terms of relative weight expressed as indices, and the resulting Seismic Landslide Susceptibility index of an area is given by the average of the indices of the first two factors multiplied by the index of the third factor. The result of this susceptibility zonation applied to Campania shows a good agreement between the distribution of the historical earthquake-triggered landslides and the highly susceptible zones.

Knowledge of the declination and inclination of the total and induced magnetization vectors is normally required for the interpretation and analysis of magnetic anomalies. A new method of estimating the direction of the total magnetization vector of magnetized rocks from magnetic anomalies is proposed. The unknown declination and inclination ( D * T and I * T ) can be found by applying a reduction-to-the-pole operator to the measured anomalies for different couples of total magnetization direction parameters ( D T and I T ) and by observing the variation of the anomaly minimum as a function of both D T and I * T .and D * T are estimated using the maximum of this function. Comparing our method to previous methods, one advantage is that our estimates are not zero-level dependent; furthermore, the method allows inclinations to be well estimated, with the same accuracy as declinations; finally declinations are not underestimated. Our method is applied to a real case and meaningful results are obtained; it is shown that the feasibility of the method is improved by removing the low-frequency components.

In this paper we present and analyze the new detailed aeromagnetic data set resulting from a recent survey car- ried out in the Phlegrean Fields volcanic area. The survey was aimed at gaining new insight into the vol- canological characteristics of the region north of Phlegrean Fields (Parete-Villa Literno area) where remarkable thickness of volcanic/sub-volcanic rocks were found in wells. Measurement of total magnetic field was per- formed on two different flight levels, 70 m and 400 m above the ground surface, along flight lines spaced 400 m apart. Both aeromagnetic maps show the noisy effect of linear anomalies evidently due to the presence of rail- way lines. To filter out these local anomalies a method based on discrete wavelet transform was used, allowing an accurate local filtering and leaving the rest of the field practically unchanged. The filtered data set was inte- grated with the existing Agip aeromagnetic map of the Phlegrean Fields, leading to a new aeromagnetic map of the whole Phlegrean volcanic area. The compilation of the pole reduced map and of the maps of the Analytic Signal and of the Horizontal Derivative of the integrated data set represents a first step for the interpretation of the maps in terms of geological structures of the whole Phlegrean volcanic district.

The Campanian volcanism develops near the sea. Therefore, the geophysical study of the marine environment is a key to a better understanding of the tectonic evolution and the origin of volcanism in the area. An abundance of high quality seismic data in the marine sector, where little direct information is available, is critical to the study of Campanian volcanism. This paper concerns the reprocessing of a seismic reflection dataset acquired in Naples Bay and processed during 1973. Even though the overall data quality was high for that time, of course their acquisition technological limits have been overcome by the new processing. Our reprocessing aimed at: 1) reduction of random noise in the data; 2) removal of unwanted coherent events; 3) reduction of spatial aliasing by means of trace interpolation on Commod Shot Point (CSP) gathering; 4) improvement of resolution of the seismic wavelet with spiking deconvolution algorithms and finally 5) reposition of reflectors in their correct locations in the space-TWT domain by means of dip moveout and post-stack time migration. A comparison between the new and old data shows that the new sections are characterized by a much higher S/N ratio. Diffraction hyperbole has been collapsed. Reverberations, ghosts and multiples have been removed or greatly attenuated, especially between the reflectors of interest, allowing us to follow them with more detail and with greater continuity. Furthermore, data resolution has been boosted by the reprocessing, allowing the interpreter to evaluate reflector position and continuity in greater detail. The reinterpretation phase of such lines, that is already in an advanced stage, will therefore allow us to gain new insights into the structural setting of the bay, with the aim of exploring the connection between tectonics and volcanism.

Since the Sixties, the turning point marked by the Plate Tectonics global theory has provided new ideas for the interpretation of the complex geodynamic evolution of the Mediterranean area. The renewed interest that followed gave a strong impulse to the geological and geophysical investigations of the Mediterranean area and, more specifically, of the Tyrrhenian Basin. Therefore, large scale geophysical surveys and oceanographic cruises were carried out until the end of the Eighties to fill the gap of geophysical information existing in the area until then. Afterwards, short scale surveys were prevalent to improve the detail of the information in areas of geodynamic interest. The gathered data sets allowed new models to be formulated, improving the knowledge of the crustal and lithospheric structure of the Tyrrhenian Basin (and surrounding areas) and the reconstruction of its complex geodynamic evolution. In this frame, the contribution of gravity and magnetic investigations has been unquestionable and deserves a wide-ranging review both on large and small scale. The main features of the potential fields resulting from these surveys will be described and the interpretative models suggested by several authors will be summarized.

Volcanic areas often show complex behaviour as far as seismic waves propagation and seismic motion at surface are concerned. In fact, the finite lateral extent of surface layers such as lava flows, blocks, differential welding and/or zeolitization within pyroclastic deposits, introduces in the propagation of seismic waves effects such as the generation of surface waves at the edge, resonance in lateral direction, diffractions and scattering of energy, which tend to modify the amplitude as well as the duration of the ground motion. The irregular topographic surface, typical of volcanic areas, also strongly influences the seismic site response. Despite this heterogeneity, it is unfortunately a common geophysical and engineering practice to evaluate even in volcanic environments the subsurface velocity field with monodimensional investigation method (i.e. geognostic soundings, refraction survey, down-hole, etc.) prior to the seismic site response computation which in a such cases is obviously also made with ID algorithms. This approach often leads to highly inaccurate results. In this paper we use a different approach, i.e. a fully 2D P-wave «turning ray» tomographic survey followed by 2D seismic site response modeling. We report here the results of this approach in three sites located at short distance from Mt. Vesuvius and Campi Flegrei and characterized by overburdens constituted by volcanoclastic deposits with large lateral and vertical variations of their elastic properties. Comparison between 1D and 2D Dynamic Amplification Factor shows in all reported cases entirely different results, both in terms of peak period and spectral contents, as expected from the clear bidimensionality of the geological section. Therefore, these studies suggest evaluating carefully the subsoil geological structures in areas characterized by possible large lateral and vertical variations of the elastic properties in order to reach correct seismic site response curves to be used for engineering projects.

In this paper we present a study of the structural setting of the volcanic island of Ischia by the analysis and interpretation of high-resolution aeromagnetic and self-potential data recently acquired over the island. The magnetic data allowed us to locate the main anomaly sources and lineaments of the island and its offshore surroundings, while the self-potential (SP) data provided information on both the structural pattern of the resurgent caldera and the high-temperature fluid circulation. An inversion of the acquired magnetic and SP data, and a joint modelling of the magnetic data and of a previous gravity data set along a SW–NE profile allowed us to build a model of the island. The model is characterized by the presence of an igneous–very likely trachytic–structure, whose top is located at 1200–1750 m b.s.l. Such a body, possibly formed by several neighbouring intrusions, has a density contrast with the pyroclastic cover of about 0.4 gr/cm 3 and its central-western part, below Mt. Epomeo, seems to be demagnetized. The demagnetization should be connected to the high geothermal gradient measured in this portion of the island and may be due to hydro-chemical alteration processes and/or to the possible presence of partially melted spots within the intrusion. Our outcome is consistent with the results of previous geophysical, geo-volcanological and geothermal studies.

This paper presents a study of the Phlegrean Fields-Ischia submarine ridge by the analysis and interpretation of high-resolution aeromagnetic data recently acquired in the Western Procida offshore. The investigated area is located along the ridge connecting Ischia to the Phlegrean Fields and is characterized by the existence of several monogenetic volcanoes aligned on a NE-SW system of faults. The high-resolution magnetic data yielded new information on the area, highlighting particularly the signature of a volcanic body located between Pt. Serra and the Ruommoli shoal. This structure has not been clearly described before and we named it as the Pt. Serra submarine volcano. The computation of the analytic signal and horizontal gradient of the data distinctly located this structure and definined the position of its rims. A 2D modeling and 3D inversion of data provided information on the volcanos thickness, width and magnetization, disclosing a meaningful igneous body extending down to several hundred meters b.s.l.

La pericolosità sismica : dalla classificazione sismica alla microzonazione dei territori comunali, alla risposta sismica del sito (con particolare attenzione alla Campania)

We show how a denoising technique based on the wavelet transform can be used to deal with localized noise related to DC electrified railway lines. This method, which performs localized and sharp filtering of cultural noise, was applied to high-resolution aeromagnetic data acquired in the Phlegrean volcanic area, southern Italy, in 1999 and 2001. The helicopter-borne survey was aimed at giving new detailed insights into the distribution of the magnetization of the area and, therefore, into the volcanological characteristics of the region. The surveyed area is characterized by the presence of towns, buildings and DC electrified railway lines whose magnetic effects influenced the measurements and were responsible for some of the measured anomalies. This cultural noise has, therefore, to be minimized as much as possible in order to allow the data to be interpreted accurately. Due to the excellent space-scale localization properties of the discrete wavelet transform, the cultural disturbance was removed very precisely, leaving the field in the adjacent areas unchanged.

The gravity anomaly field of the Tyrrhenian basin and surrounding regions reflects the complex series of geodynamic events active in this area since the Oligocene–Miocene. They can resume in lithospheric thinning and asthenospheric rising beneath the Tyrrhenian Basin, coexisting with the roll-back subduction of the African plate margin westward sinking beneath the Calabrian Arc. The geographic closeness between these processes implies an intense perturbation of the mantle thermal regime and an interference at regional scale between the related gravity effects. A model of the litho-asthenospheric structure of this region is suggested, showing a reasonable agreement with both the evidences in terms of regional gravity anomaly pattern and the results concerning thermal state and petro-physical features of the mantle. The first phase of this study consisted of the computation of the isotherms in the crust–mantle system beneath the Tyrrhenian Basin and, afterwards, of the density distribution within the partially melted upwelling asthenosphere. The second phase consisted of a temperature/density modelling of the slab subducting beneath the Calabrian Arc. Finally, a 21 / 2 interpretation of gravity data was carried out by including as constraints the results previously obtained. Thus, the final result depicts a model matching both gravity, thermal and petrographic data. They provide (a) a better definition of the thermal regime of the passive mantle rise beneath the Tyrrhenian basin by means of the estimation of the moderate asthenospheric heating and (b) a model of lithospheric slab subducting with rates that could be smaller than generally suggested in previous works.

An application of magnetic survey to the submerged Roman ruins of the Bay of Baia, volcanic area of the Phlegrean Fields, Naples (southern Italy) is presented and discussed. The site of Baiae, one of the most extensive submerged archaeological sites known in Italy, is characterized by urban sites with residential houses, thermal baths, fisheries and harbour buildings. The survey was aimed to establish the typical magnetic signatures of building structures submerged in a volcanic marine environment. The comparison of both the maps of the magnetic anomaly field and of the computed analytic signal with the known submerged archaeological structures of the area gave some interesting insights into the lithological characteristics of the archaeological structures of the Baiae site and showed the effectiveness of the magnetic method for mapping remnants of building structures beneath the sea bed. Copyright © 2005 John Wiley & Sons, Ltd.

We here present and discuss the results of the analysis and qualitative interpretation of two magnetic surveys performed in the Bay of Naples in 1998 and 2000. A map of the Bay of Naples based on the data acquired during these surveys has already been published by the Italian CNR-IAMC Research Institute. We re-processed the same data to produce maps of the pole reduced, analytic signal and horizontal derivative data and correlated them with the bathymetry and the gravimetric data of the area. The analysis shows strong anomalies in the NW and NE volcanic areas of the Bay of Naples, while the central area seems magnetically quiet. In the Phlegrean area the maps clearly show the southern rim of the Phlegrean caldera and demonstrate that while the Magnaghi Canyon is correlated to gravimetric highs and magnetic structures, and can therefore be interpreted as an active lineament, most of Dohrn Canyon is not characterized by volcanic activity and does not correlate to any gravimetric or magnetic structures. An important round-shaped magnetic anomaly is for the first time identified in the central slope of the gulf between the two canyons, probably correlated to a large buried volcanic edifice. In the Vesuvian area some intense circular anomalies, aligned in the NNW–SSE direction, are localized in the Torre del Greco and Torre Annunziata offshore, related to the submerged part of Vesuvius and possibly connected to buried vents.

We start from the general inverse problem for potential fields and discuss the validity and suitability of using not only horizontal variations of them, but also their vertical ones. Hence multilevel data sets are considered, being they obtained either from measured data at different levels or by measuring the field just at the lower level and then generating by upward continuation the data at the remaining upper levels. In the latter case the upward continued data must be considered as the true ones plus some errors due to experimental errors and to the fact that they are generated from a discrete data set known on a finite survey area. Several forms of a priori information, such as that assuming the source can be represented by a fault or a sheet sandwich model, may allow the information contained in multilevel data to be effectively used for the interpretation of gravity and magnetic data. Recently established techniques of analysis, such as the continuous wavelet transform, are applied successfully to potential fields using implicitly the information contained in multilevel data. Assuming a block model for the source domain, the upward continuation formula may help to improve the solution of either 1D, 2D or 3D inverse problems enlarging the system with the equations related to the vertical variations of the fields, thereby reducing the algebraic ambiguity. Meaningful and computationally suitable quantities, such as weighted averages of potential fields, are also closely related to the use of multilevel data, providing useful insights for the determination of the depth distribution of the sources.

P203 MULTICHANNEL ANALYSIS OF SURFACE WAVE AND 2D SEISMIC REFRACTION TOMOGRAPHY – VP AND VS ESTIMATION IN PYROCLASTIC SOILS Abstract Figura 1: Geological map of Campi Flegrei volcanic area. 1: regional faults. 2: caldera rims. 3: Campi Flegrei active area. 4: Quaternary deposits. 1 The detailed knowledge of S and P-wave velocities (Vs and Vp respectively) distribution in the nearsurface of a heterogeneous area characterized by unconsolidated soils is crucial to estimate the subsurface geological and geotechnical conditions. In fact the elastic properties of near-surface material and their effects on seismic wave propagation are controlled by the presence of ground

Geopotential data may be interpreted by many different techniques, depending on the nature of the mathematical equations correlating specific unknown ground parameters to the measured data set. The investigation based on the study of the gravity and magnetic anomaly fields represents one of the most important geophysical approaches in the earth sciences. It has now evolved aimed both at improving of known methods and testing other new and reliable techniques. This paper outlines a general framework for several applications of recent techniques in the study of the potential methods for the earth sciences. Most of them are here described and significant case histories are shown to illustrate their reliability on active seismic and volcanic areas.

Magnetization and density models with depth resolution are obtained by solving an inverse problem based on a 3-D set of potential field data. Such a data set is built from information on vertical and horizontal variations of the magnetic or gravity field. The a priori information consists of delimiting a source region and subdividing it in a set of blocks. In this case, the information related to a set of field data along the vertical direction is not generally redundant and is decisive in giving a depth resolution to the gravity and magnetic methods. Because of this depth resolution, which derives solely from the potential field data, an unconstrained and joint inversion of a multiobservation‐level data set is shown to provide surprising results for error‐free synthetic data. On the contrary, a single‐observation level data inversion produces an incorrect and too shallow model. Hence, a good depth resolution is likely to occur for the gravity and magnetic methods when based on the information along the vertical direction. This is also evidenced by an analysis of the kernel function versus the field altitude level and by a singular value analysis of the inversion operators for both the single and multilevel cases. Errors connected to numerical upward continuation do not affect the quality of the solution, provided that the data set extent is larger than that of the anomaly field. Application of the method to a 3-D magnetic data set relative to Vesuvius indicates that the method may significantly improve interpretation of potential fields.

During the fall of 1998, an accelerometric digital (vertical component) station has been installed in two contigous sites located at the towns of Castelluccio Inferiore (CI) and Castelluccio Superiore (CS) (Calabrian Lucan Appennines, Southern Italy), with the aim of the evaluation of the seismic site response at Castelluccio Inferiore. This area is very important because in the last centuries has been interested by large earthquakes. At present the Lucanian Appenines represent a major boundary between two distinct seismotectonic areas: the Southern Appenines, characterized by NW-SE striking active normal faulting and the Calabrian-Sicilian area with EWE-WSW striking active normal faulting. Both areas are interested by earthquakes of magnitudo up to 6-7° Richter. (Turco et al.,1990; Selvaggi et al.,1997; Kiratzi, 1994; Hyppolite et al.1994). The accelerometric station was made by a piezoelettric vertical sensor with frequency response flat in 1-100 Hz. The analogic signal was digitalized by a 16 bit A/D board and finally recorded on the mass storage of a PC.The data was collected in a time interval that allowed the recording of a considerable number of seismic events in two different sites. At the first site (CS) the power spectra is referred to the bedrock because the sensor is located on lapideus rocks (limestones), at the other site (CI) the seismic response is filtered by a 25 m thick Plio-Pleistocenic overburden constituted by shale and clay with very low seismic rigidity (vp ~ 700 m/s; ρ ~ 1.1 g/cmc).

A boundary analysis of the gravity and magnetic fields of the Phlegrean Fields volcanic area and of the surrounding Campanian Plain reveals a complex structural setting. The Campanian Plain results well defined from sharp density boundaries. A set of major E–W lineaments occurs within the Plain. We derive a framework of the structural control to the volcanological evolution of Campanian Plain, which appears strongly influenced by a set of NE–SW lineaments bordering the Acerra depression. The density and magnetization boundaries of the Phlegrean Fields are significantly consistent, both indicating for the collapsed Phlegrean caldera an area considerably less extended than that based on previous geologically-defined models. Many other structures are evidenced in the Phlegrean area, often with agreement between density and magnetization boundaries. Inside the caldera, a strong consistence between the structures we identified and recent seismicity has been noted.

This paper deals with the analysis of aeromagnetic data on the Sonma-Vesuvius area. An inverse 2.5D method is used, its main features being a variable strike length and a data set relative to a vertical plane. This last provides a depth resolution, so that the result consists in a magnetic tomography along a vertical section. The magnetic model shows that magnetized rocks extend up to carbonate basement depths (about 2 km). The stronger magnetizations (>6 A/m) are concentrated in the emerged part of the volcano, but high magnetizations are still present down to about 1800 m b.s.l. The magnetization distribution found is then compared to the distribution of;he hypocenters of Vesuvian earthquakes and for shallow depth a positive correlation is noted. At depths greater than about 2 km, i.e. at the level where a geothermal well started to encounter dolomites, the model shows no magnetization, while hypocenters form a nearly continuous vertical belt. This pattern leads to the conclusion that this evidence may be considered as being due to a small volume of the feeding system at these depths or eventually as an indication of strong alteration processes of magnetic rocks. (C) 1998 Elsevier Science B.V. All rights reserved.

It is here presented an attempt of quantitative evaluation of the limits of applicability of 1D modelling for evaluation of the site seismic response when dealing with a non horizontal basement. The dynamic evaluation of the numerous situ elastic parameters needed for a correct 2D modelling can represent a considerable part of the economie resources of a project. Therefore it is important to understand the limits of the ID modelling in order to mini mise the expenses without dangerous errors when evaluating the seismic hazard. The response of the most used elastic non-linear 1D and 2D algorithms have been used, in order to estimate the seismic site response. A non-horizontal basement has been modelled for various angles of dip up to 30°. The reference accelerogram is relative of the Umbria earthquake of Colfiorito (ltaly, 26/09/97, M=5.6), recorded at the Department of Geophysics and Volcanology - University of Naples Federico II. The results evidenced that if the dip of the basement is less than 20°, the evaluation of the site response given by the 1D and 2D models is almost similar. For dip values exceeding 20° the DAF spectra starts to diverge, both in terms of amplitude and peak period, therefore the response of the lD models is inaccurate. In these geological conditions the 1D algorithms should not be used for DAF evaluation. The theoretical determinations have also been tested in a real site located in the city of Naples, characterised by a 32° dipping volcanic tuff basement. The results show that the theoretical outcome can be extrapolated to that particular site.

The results of the 2.5-D gravity modelling of the litho-asthenosphere system in the Central Mediterranean, along two regional geotransects, are presented and their possible implications for the geodynamical evolution of this area are discussed. Particularly, gravity data on the Tyrrhenian and Provencal-Balearic basins were interpreted introducing significant constraints by means of several main petro-physical parameters tied to the litho-asthenospheric evolution during the extensive tectonics. By this approach, based on the model of McKenzie and Bickle (in: J. Petrol., 29. pp. 625–679. 1988) and White and McKenzie (in: J. Geophys. Res., 94, B6, pp. 7685-7729, 1988), the estimation of the vertical density distribution in the lithosphere-asthenosphere system has been possible. Significant differences in the gravity anomaly field occur when different density models of asthenospheric upwelling are considered. This depends on factors like the thermal regime, the stretching of the lithosphere and its thickness before it. The obtained results contributed to the validation of models interpreting the origin of the Tyrrhenian and Ligurian-Provencal basins as related to a passive extensional process rather than to the presence of an active upwelling asthenosphere beneath the Central Mediterranean basins.

Fifteen seismic reflection lines from AGIP surveys, in and around the Campanian Plain and Mt. Somma–Vesuvius (south Italy) have been interpreted. The attention has been focused to the horizon pertinent to the top of the Mesozoic carbonate sequence and the Quaternary faults dissecting it. As a matter of fact, both are very important elements for understanding the origin of the volcanic activity in the area, that often in the past, has been the topic of debates not supported by reliable data. In the study area, referring to the depth of the carbonate basement, comparison between the result achieved by the seismic prospecting and previous gravity studies has been made. It shows coherence in some areas but large discrepancy within others. Near the town of S. Anastasia, the gravity and seismic depth estimates differ as much as 1000 m or more. Furthermore, the seismic data show that the source of the greatest volcanic eruption in the area (the so-called `Campanian Ignimbrite') is probably not located in the Acerra depression, as suggested by other authors. A main NE–SW fault directed toward Vesuvius, considered as playing a primary role on volcanogenetic processes and previously recognised only offshore by marine seismic survey, has been now identified also inland using this new seismic information. The results presented here strengthen the hypothesis that Mt. Vesuvius is located at the crossing point of two regional Quaternary sets of fault heading NW–SE and NE–SW.

Analysis of the analytic signal of the aeromagnetic field in the Tyrrhenian region allowed the systematic location of the boundaries of magnetic shallow sources. This method was chosen because of its independence from the magnetization and inducing field direction, and the results were similar to those of the boundary analysis of the horizontal gradient of the pseudogravity transformed field. The analytic signal was computed by a stable algorithm based on the second order horizontal derivatives of the field and Laplace equation. The complexity of the investigated area is well reflected in the aeromagnetic field and an objective and systematic study, such as boundary analysis, provided a rather complete description of the main regional structures. Significant trends indicated the existence of structures, whose nature was still unknown or uncertain. These included structures located between the Vavilov and De Marchi seamounts, NW of Stromboli Island, south of Ponza Island, a buried horst immediately south of the Cilento coastline, a body located northwest of the Cassinis seamount and other small magnetized structures located south of the Tuscanian archipelago. In many cases, a better definition of several structures previously recognized was obtained as in the case of some tectonic alignments (e.g., the Elba ridge, the Romolo and Selli lines, etc.), a large number of igneous seamounts (e.g., Magnaghi, Marsili, Vavilov, Anchise, Quirra, Enarete, Eolo and Sisifo seamounts) and several crystalline outcrops (e.g., Ichnusa, Vercelli, M. della Rondine, Tiberino, Cassinis, Traiano, Glauco and Augusto seamounts).

Gravity modelling of the litho-asthenosphere system in regions involved in extensional tectonics requires an accurate estimation of the vertical density profile in the upwelling asthenosphere. To this end, the calculation of the variation of several parameters is needed, i.e., the degree of thermal anomaly in the asthenosphere, the amount of stretching, the thickness of the lithosphere before stretching, and the variation of melt fraction generated by adiabatic decompression. Therefore, knowledge of melt density and of the residual mantle rock composition is necessary in order to have the information to calculate the density of the uprising mantle. These calculations allow to partially solve the problem related to ambiguity of the gravity interpretation, and to provide information about the structural features of the upwelling mantle.

Magnetic anisotropy measurements on samples from the lower continental crust were made to test the hypothesis that anisotropy may cause deflection of the peak-to-trough axes of magnetic anomalies caused by mid- to lower crustal sources. Average anisotropy (P′) for these samples is 1.5 but can be as high as 3.4. Felsic granulite facies rocks show the highest anisotropy. Magnetic sources with P′ equal to the maximum determined in this study can cause azimuthal rotations of magnetic anomalies by up to about 25°, but P′ lower than or equal to 1.5 causes no significant rotation. Comparison of the model results to the abnormal shape of some magnetic anomalies in southern Italy indicate that these anomalies cannot be related easily to a strong and coherent AMS of the source rocks. The most probable explanation of such shapes is the existence of a strong remanent magnetization in subsequently rotated source bodies.

At 0132 UTC (0332 local time) on 6 April 2009, a major earthquake (ML = 5.8, Mw = 6.3) occurred a few kilometers southwest of the city of L'Aquila in the Abruzzi region of central Italy (http://earthquake.usgs.gov/eqcenter/eqinthenews/2009/us2009fcaf/). The quake was preceded by a long and often intense seismic sequence, and it was followed by a series of aftershocks. The extensive damage from the major earthquake resulted in about 300 fatalities, 1200 injuries, and 40,000 evacuees, suggesting widespread ground motioneffects and Mercalli-Cancani-Sieberg (MCS) scale intensities of up to level IX (http://portale.ingv.it/ primo-piano-1/news-archive/2009-news/april-6-earthquake/copythe-l-aquila-seismic-sequence-april-2009/view?set_language=en). Such intensity levels correspond to an impact on buildings, in terms of maximum ground horizontal acceleration, as great as 0.6 g, where g is the acceleration of gravity. An acceleration of about 0.6 g actually was measured by accelerometric stations in the L'Aquila valley (http://mceer.buffalo.edu/infoservice/disasters/ground-motion-summary.pdf).

An extensive analysis of aeromagnetic data from the Italian region is presented, regarding the evaluation of the azimuthal direction of the total-magnetization vector. A method based on the Zietz and Andreasen (1967) correlation between anomaly shape and direction of the total magnetization vector was used. A discussion related to possible traps in using this method is presented, with the aid of several tests on synthetic anomalies. The analysis points out a number of anomalies revealing abnormal directions, either SW-NE or SE-NW, which were used to divide the investigated area into five regions with different trends. Finally, assuming elevated Koenigsberger ratios for the source-rocks, the declinations of the remanent magnetization vector were judged very similar to those estimated for the total-magnetization vector. Thus, by comparing these values with the normal declination of the area, rotation values of the crustal blocks related to the investigated anomalies were proposed. Finally, these were compared with the available geological and palaeomagnetic information and significant correspondences were found.

In this paper we present an example of the integration of airborne and marine magnetic data sets measured in the Neapolitan area, southern Italy. The integration involved detailed data measured recently in the Phlegrean Fields, in the Somma-Vesuvis area and in the Bay of Naples, that produced a high-resolution magnetic map of the whole active volcanic district. The data sets partially overlapped and characterized varying flight height and line spacing. Integration was therefore performed through several procedures including continuation between general surfaces. The integration produced a new, detailed, draped magnetic data set of the Neapolitan region characterized by a terrain clearance of 200 m, giving a meaningful overall view of the volcanic area. The study of the main magnetic features of the area was carried out by computing the horizontal gradient of the pole-reduced draped data. The analysis of the obtained map showed the presence of lineaments of preferential magma upwelling and buried volcanic structures and allowed the delineation of a geovolcanological and structural framework of the whole Neapolitan volcanic district.

This paper focuses on the recent tectonic evolution of the Bay of Naples with the aim of exploring the connection between local tectonics and volcanism. We reprocessed the seismic reflection dataset acquired in the area in the late 1973. The new processing was highly successful in obtaining a decisive strong reduction of random noise, removal of coherent noise and reduction of spatial aliasing. Classical interpretative schemes and complex attributes of seismic traces were used to reconstruct fault kinematics and reflector patterns. The results show that the faults affecting the Bay of Naples exhibit prevailing NE structural strikes, with the exception of the Pozzuoli Caldera where NW patterns are also common. Many faults are subvertical and show seismic evidence of volcanic activity along them. A main alignment of conjugate NE-SW faults, named here as "Magnaghi-Sebeto line", intersects several submarine volcanic banks and separates the bay into two sectors, characterized by important geological, geophysical and petrochemical differences. The structural configuration of the bay may reflect the occurrence of either oblique extension or a transfer zone of the NW-SE fault system, along which, in the Campanian-Lucanian Apennine chain, great vertical displacements occur. © 2003 Elsevier B.V. All rights reserved.