GNGTS 2014 - Atti del 33° Convegno Nazionale

Analytic signal and magnetic field moduli analysis �� ������ in Europe M.Milano, M. Fedi Università degli Studi Federico II di Napoli, Italy Introduction. Working with a two-dimensional magnetic field data, an important goal is to process the data in order to better evidence the complex information of the original data. One of these procedures is to produce a map in which the shape of the anomalies is more directly linked to the physical properties of the sources. In this work we studied the European magnetic field at different levels from the Earth surface in order to analyze the different components of the magnetic field related to lithospheric sources by the application of methods removing the dipolar shape of the anomalies: the field modulus and the analytic signal modulus. This is important to get a rapid distinction among anomalies of normal or reversed polarization. Methods. In the last decades the analytic signal modulus and magnetic field modulus have been of great utility to interpret potential field data, helping to localize in a very simple way the edges of the sources and their horizontal position without specifying a priori information about source parameters and. We define the modulus of the magnetic field (| F |) as: (1) where F x , F y e F z are the three components of the total magnetic field along x, y and z respectively. The advantage of this operator is the removal of the dipolar behavior of the magnetic anomaly field, placing its maximum amplitude toward the barycenter of the anomaly sources. The analytic signal is defined by: (2) where , and are the derivatives of the total-intensity component of the magnetic field ( T ) with respect to the directions x, y , and z . The advantage of this method, compared to the calculation F modulus, is to have a complete independence from the variation of magnetic inclination ( I ) (Nabighian, 1972) in the case of 2D fields (profiles). In the 3D case such independence has not been proven mathematically, but we can assume that it is only weakly dependent on the direction of F . | A | has a higher resolution than | F |, and this is very useful when some problematic phenomena make more difficult the interpretation of anomalies, for example the effect of coalescence between single anomalies. Aeromagnetic data and main European magnetic field features. The area covered by the data has an extension of: 20°W, 57°N; 45°E, 57°N; 35°E, 37°N; 5°W, 37°N. Aeromagnetic data used in this work are extracted from the European and Mediterranean Magnetic Project (Fletcher et al. , 2011). The EMMP aimed at bringing together all the available magnetic data (ground, air and marine, profiles and data network) to obtain a 1 km high- resolution grid of total-intensity magnetic field (TMI). In order to observe the various contributions of lithospheric sources placed at different depths, the aeromagnetic data were upward continued at many levels from the Earth surface. Since the aeromagnetic data are originally gridded at a 1 km surface from the topography, the first step was to upward continue the data at 5 km altitude from the Earth surface using a DEM SRTM30. Than data were upward continued up to satellite altitudes (400 km) (Fig. 1) using the following level-to-level formula: (3) where U ( x,y,z ) is the potential upward continued field at the scale z , U ( ξ,η,0 ) is the potential of 166 GNGTS 2014 S essione 3.2