Index
Table of contents
Total Field Magnetic Anomaly Map of Italy and
Surrounding Marine Areas at Sea Level.
Recent Compilation and Scientific Significance
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A. Meloni , C. Carmisciano , M. Chiappini , O. Faggioni and I. Marson
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Istituto Nazionale di Geofisica e Vulcanologia, via di Vigna Murata 605, Roma, Università di Trieste and OGS
Summary
A shaded relief magnetic anomaly map of total intensity of the Earth’s magnetic field for Italy and the
surrounding seas has been produced at sea level, for the geomagnetic epoch 1979.0 (see Chiappini et
al., 2000). Magnetic observations were made on shore within the framework of Progetto Finalizzato
Geodinamica of the Consiglio Nazionale delle Ricerche (PFG-CNR) between 1977 and 1981. The off
shore data were taken during the period 1965-1972 by the Osservatorio Geofisico Sperimentale
(OGS). This new compilation gives an unprecedented view of the magnetic anomaly field of the whole
area at ground level, which contains many imprints of the major tectonic elements of Italy, and
portrays their regional characterization. In 2004 Caratori et al. have undertaken a detailed reprocessing
of old aeromagnetic data taken by AGIP at the national scale, with the inclusion of new data. For the
first time now the ground level map and the aeromagnetic map show the existence of common features
that allow comprehensive correct scientific investigations.
Introduction
Similarly to gravity, also in the case of magnetic anomalies the geophysical work required to reach
scientific results follows a three step process: a) measurements are taken in the field at the ground, sea
surface or above, b) data elaboration, that will lead to anomalies and graphical tools, like maps, and
finally c) interpretation of results, basing on knowledge of the geology of the investigated area. In
Italy, if we exclude local or regional scale magnetic investigations, efforts on a national scale devoted
to realization of a national scale magnetic anomaly map started in the 1970s. Under the framework of
the Progetto Finalizzato Geodinamica (PFG, sponsored by Consiglio Nazionale delle Ricerche CNR),
Istituto Nazionale di Geofisica (ING, now INGV) involving also several Universities, carried out a
first and second order ground magnetic network for the determination of total field (and other
magnetic field elements) across the Italian peninsula and major islands. This work brought to the first
ground magnetic total field anomaly map for the land areas (Molina et al., 1985; CNR-PFG, 1986 also
in Molina et al., 1994). In the same years the Osservatorio Geofisico Sperimentale (OGS) started a
long series of geophysical investigations in the Mediterranean sea including magnetics (total magnetic
field) and published a few sector maps for the seas surrounding Italy (Morelli et al., 1969; Morelli,
1970; Morelli, 1972).
Methodology
Only around the year 2000 INGV, with the involvement of the then Istituto di Geofisica Marina of
Consorzio Universitario di La Spezia (CUNISPE) and the OGS, launched and coordinated a program,
for the realization of a digital database of magnetic anomaly, for the Italian land area and the
surrounding seas by means of the compilation of all existing marine and ground total magnetic field
data all over and around the Italian peninsula. The realization of an integrated total magnetic field
anomaly map took advantage of the most recent data processing techniques and the experience
gathered during the last years. The merged color shaded relief magnetic anomaly map is the final
result of this coordinated work (see Chiappini et al., 2000).
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For what concerns aeromagnetic investigations the Italian national Oil Company AGIP commissioned
an aeromagnetic survey of Italy to a private company in the early 1070s. AGIP collected all total field
magnetic data at various altitudes and drew a first aeromagnetic anomaly map for the Italian territory
in 1981 and a later contour version superimposed to regional geological features in 1994 (AGIP, 1981;
Cassano et al., 1986, Servizio Geologico Nazionale, 1994). Due to the high measurements density and
the large geographical extent, the resulting data set has been the reference tool for magnetic
interpretations for many years, and to a larger extent, a tool for integrated geodynamical
interpretations of geophysical data. Only in 2005 a revised aeromagnetic map of Italy and surrounding
seas was undertaken also including new surveys data. The detailed reprocessing of aeromagnetic data
at the national scale, the inclusion of the new data, the subtraction of an appropriate reference level,
are the main reasons for the actual enhancement of the anomaly definition emerging from this new
compilation. (Caratori et al., 2004).
Figure 1. Sea level total magnetic field anomaly map for Italy and surrounding areas.
Conclusions
A comparison of the old maps was quite difficult until these new products were published. In fact the
areas covered in the surveys were substantially different and many differences also emerged in the
anomalies in various regions. So far the observed diversity could not be easily interpreted because of
the partial covering of magnetic anomalies on the ground and the much larger geographical extent of
the aeromagnetic map. However a limited correlation of the two, in some areas of Italy, was evident,
showing remarkable differences, especially in long wavelength magnetic features. After the recent
works by Chiappini et al. (2000) and Caratori et al. (2004) we can now confirm that this discrepancy
was due mainly to an incorrect removal of the reference field in the old aeromagnetic compilation. A
comparison between the new anomaly map at the sea level and the new aeromagnetic survey for the
whole area, clearly shows that much better investigation tools are now available for users for studying
the magnetic anomaly field at different altitudes in Italy.
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Innovation in EM, Grav and Mag Methods:a new Perspective for Exploration
Capri, Italy, April 15 – 18, 2007
In this paper, after a general information on reduction and processing procedures, the overall
scientific result that emerged from the final compilation of the sea level map will also be briefly
discussed.
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EGM 2007 International Workshop
Innovation in EM, Grav and Mag Methods:a new Perspective for Exploration
Capri, Italy, April 15 – 18, 2007