Caratori Tontini, Fabio

The use of the integral moments for interpreting magnetic data is based on a very elegant property of potential fields, but in the past it has not been completely exploited due to problems concerning real data. We describe a new 3-D development of previous 2-D results aimed at determining the magnetization direction, extending the calculation to second-order moments to recover the centre of mass of the magnetization distribution. The method is enhanced to reduce the effects of the regional field that often alters the first-order solutions. Moreover, we introduce an iterative correction to properly assess the errors coming from finite-size surveys or interaction with neighbouring anomalies, which are the most important causes of the failing of the method for real data. We test the method on some synthetic examples, and finally, we show the results obtained by analysing the aeromagnetic anomaly of the Monte Vulture volcano in Southern Italy.

The final aim of a magnetic survey is to obtain quantitative information about the geological source generating the observed field. In this paper, I show how the employment of a suitable non-iterative operator in the Fourier domain permits to recover the horizontal magnetization distribution of a plausible equivalent source by a simple deconvolution. The results obtained in the synthetic case show a good agreement with the generating model, and moreover the recovered magnetization map appears more stable concerning high-frequency noise amplifi-cation with respect to other operators previously used in literature. The analytic justification of this stability will be described in detail by comparison with the traditional operators. The extension of this operator to the sector of field transformations, such as Upward Continuation or Reduction to the Pole, is straightforward because it is sufficient to re-calculate the field due to the apparent magnetization distribution. The results obtained by synthetic and real data tests demonstrate that the equivalent-source operator shown in this paper is able to give meaningful answers with a minimum amount of information by the user concerning depth of the source. These parameters as known, when unavailable, can be estimated in a stable way from the power spectrum of the magnetic anomaly, so that in the final analysis only a Fourier transformation of the data is needed to evaluate a realistic magnetization model.

In questo lavoro vengono presentati i risultati derivanti da analisi dei dati della nuova Carta Aeromagnetica d’Italia (Eni Exploration & Production division e Cunispe, 2002) relativi all’area del Tirreno centrale mediante le tecniche di filtraggio direzionale. L’area in analisi comprende la regione del Tirreno centrale in particolare la fascia geografica del 41° parallelo. Lungo questo parallelo sono allineate diverse strutture geologiche come, seamount, faglie profonde e le strutture vulcaniche dell’area campana.......

This work focus on the newly born DLTM, namely the Distretto Ligure delle Tecnologie Marine, based in La Spezia, Liguria Region (IT). The main involved partners are: Ministries, Regione Liguria Council, Spedia SpA Company, Industries, SMEs (SMBs), Universities and National Research Institutes. The DLTM has been created as an answer to the local versus global needs of marine products innovation, technology and science. In order to provide, both the local and international community, effective solutions the DLTM aims to: - promote Innovation and pre-competitiveness of activities related to industrial research; - enhance the value and visibility of excellence areas existing in the Ligurian region (in the big enterprises as well as in SMEs) concerning marine technology; - enhance the value of academic activities focusing their R&D on industrial products/processes, assuring, evaluating and preventing environmental sustainability also in case of extreme events; - harmonize/make sustainable the economy and the society promoting scientific innovation and technological development, by means of Universities, Public and Private Research Institutes (at regional, national and EU level); - help the exchange of ideas and realization of projects aimed at developing the District objectives; - increase the dissemination and valorisation of District results and achievements, build capacity in the sectors of interest to the District. The DLTM is characterized by two main macro-themes ......

We show an algorithm for the linear inversion of 2D surface magnetic data to obtain 3D models of the susceptibility of the source. After showing a novel characterization of the ambiguity domain in the Fourier space, which has a simple geometrical interpretation, we will demonstrate that a depth-weighting function is useful to significantly reduce the ambiguity domain in order to characterize the main source properties. The forward model is discretized by a mesh of prismatic cells with constant magnetization that allows the recovery of a complete 3D generating source. As the number of cells are normally grater than the amount of available data, we are left with an underdetermined linear inverse problem, which can be regularized in order to obtain an unique solution by a depth-weighting function, adapted from Li and Oldenburg (1996) to close the source towards its bottom. The main novelty of this method is a first-stage optimization that gives information about the depth-to-the-bottom (dtb) of the generating source. This parameter permits both the evaluation of the appropriate vertical extension of the mesh, and the definition of the shape of the regularizing depth-weighting distribution. The adopted method is suitable under appropriate changes to deal also with gravity data. After showing which kind of a priori information is introduced by this particular regularization, we will describe its limits and its possible improvements and then we will show the results of some synthetic tests. As a final application we will show the 3D magnetic model of an interesting volcanic region in Italy.

Inversion of large-scale potential-field anomalies usually proceeds in the Fourier domain, where a large amount of data can be properly addressed. The commonly adopted geometry is based on a layer of constant thickness, i.e. with a bottom level at a fixed distance from the top level. We propose a method that overcomes this limiting geometry by inverting in the usual iterating scheme for top and bottom levels of any shape. Randomly generated synthetic models will be explored both for gravity and magnetic data, and finally the good performance of this method will be tested by the real isostatic residual anomaly of the Tyrrhenian Sea in Italy. The final result is a density model that allows the investigation of the distribution of the oceanic crust in this region, which is still a point under discussion.

Two methods are commonly adopted to evaluate the optimal Bouguer density for a given data-set, starting from different data characteristics or geological regime, giving in many cases different results. We propose some simple extension of these methods in order to make their results compatible. To this aim, we have used free-air gravity satellite data from Geosat and ERS-1 missions in order to compile a Bouguer gravity map of the Mediterranean Sea. The complete Bouguer correction has been applied by using the method of Parker (1972), that acts in the Fourier domain and allows for an exact evaluation of the gravity contribution from an highly sampled topographic model of the land. The density used for the Bouguer reduction has been obtained thus from the gravity data-set itself, by using two different optimization methods that have given the same optimal result of 2400 kg/m3. We have studied the radial power spectrum of the data, choosing the optimal Bouguer density as the one that minimizes its slope, i.e. the fractal dimension of the resulting gravity map in the band of wavelength from 45 km to 105 km. The second approach consists of studying the correlation between topography and Bouguer anomaly by spatial crossplots for a significant sub-set of the data. In the past these methodologies were applied alternatively since they gave different optimization values, especially the second method that seems to ignore large-wavelength isostatic effects. The main novelty of our work is represented by the combined application of both the approaches having as common goal the reduction of the short-wavelength effects of topography in the gravity map. Actually we have revisited both the methodologies, proposing slight modifications to make their efforts compatible. Their coincident results confirm their validity of application and give reliability to the recovered value of the Bouguer optimal density. As a first result we have obtained a revised Bouguer map for the Mediterranean Sea, that is useful for large-scale geological studies. Moreover, studying the correlation between Bouguer anomaly and bathymetry, we propose the compilation of a new interpretative tool that may be considered a sort of normalized correlation map defining the 2D isostatic setting of the investigated region, without introducing any lithospheric model. In a direct way we have found that the over-all region seems to be in a complete isostatic equilibrium apart from the young basins of Tyrrhenian Sea and Aegean Sea, confirming previous similar results.

Hydrothermal alteration processes involve mineralogical, chemical, and textural changes as a result of hot aqueous #uid-rock interaction under evolving boundary conditions. These changes affect the physico-chemical properties of the rocks, enabling high-resolution geophysical prospecting to be an important tool in the detection of sea#oor hydrothermal alteration. Here we present the results of recent geophysical investigations of the Marsili and Palinuro volcanic complexes, southern Tyrrhenian Sea, during the 2010 TIR10 and 2011 MAVA2011 cruises by the R/V Urania. The new dataset includes a dense grid of multibeam bathymetry; sea#oor re#ectivity, magnetic and gravity lines; and high-resolution single (CHIRP) and multichannel seismic proYles. The surveys were focused on areas known to host intense hydrothermal alteration in order to provide a more detailed description of the Marsili and Palinuro hydrothermal systems. Ground-truthing was based on earlier discoveries of hydrothermal vents and their associated deposits, and on direct observations made by ROV dives. High-resolution morpho-bathymetry, sonar re#ectivity, rock magnetization, and density distribution together enabled us to assess the extent of sea#oor hydrothermal alteration and its relationship to local volcanic and tectonic structures. Hydrothermal alteration associated with the Marsili seamount is largely distributed along primary volcano-tectonic structures at the ridge crest. By contrast, at Palinuro hydrothermal alteration is mostly associated with secondary volcanic structures such as collapsed calderas and volcanism reactivation along ring faults. In particular, evidence for intense hydrothermal activity occurs at Palinuro where volcanotectonic features interact with regional tectonic structures.

Magnetic data play a key role in interpretation of deep sources, mostly when they are not easily investigable by other direct methods as in the case of oceanic crust. The most striking problem connected with magnetic data however, is due to their difficult quantitative interpretation that in final analysis derive from the mathematical properties of Laplace equation. Dipolarity increases these difficulties with respect to other potential fields as gravity, so that magnetic data are far from being interpretable “by eye”. The actual methods for reconstruction of crustal sources that reproduce or enhance magnetic observations will be shown, differentiated for 3D or 2D analysis, showing their benefits and/or their disadvantages if applied to marine magnetic data. We will show the results obtained applying a new linear inverse filter on a high-quality data set in the Tyrrhenian Sea, demonstrating the utility of Fourier 2D modelling when there is a large number of data to be interpreted.

We show the result obtained by the 2.5D modelling of the deep crustal structure of the nord-east termination of the Algero-Provencial basin, near the Eastern Ligurian coastline .....