Abstract

The aim of this paper is to present a high resolution magnetic anomaly map of the Bay of Naples as a contribution to the knowledge of the geophysics and volcanology of this sector of the Eastern Tyrrhenian margin. A Total Earth Magnetic Field (EMF) survey was recently performed in the Bay of Naples during an oceanographic cruise (GMS00-05-Leg II -- October/November 2000) carried out by the Istituto per l'Ambiente Marino Costiero, CNR (formerly Geomare Sud) onboard of the R/V Urania (CNR, Italy). The collected data have an advanced spatial coverage with respect to previous measurements, such as by airborne magnetic survey (AGIP, 1981; Caratori Tontini et alii, 2003). Moreover the data were acquired at a shorter distance from the source and at a lower velocity, giving more precise sampling and improved field restoration. Magnetic data have been recorded using a G-811 Proton Magnetometer; the sensor was placed in a fish towed at about 200 m from the ship and at an average depth of 15 m below sea level; moreover the magnetometer position was regularly controlled and recorded and the data were sampled at 3 sec, corresponding to an average spatial sampling of about 6.25 m (Siniscalchi et alii, 2002). The magnetic anomaly map was compiled with a grid cell size of 200 m. A colorimetric scale expressed in nT is shown on the right side of the map to quantify the intensity of magnetic anomaly measured. The main magnetic anomaly fields recognized on the map have been constrained by geologic features based on the geologic interpretation and on the correlation with high resolution Multibeam bathymetry recorded by the IAMC-CNR Institute in the Gulf of Naples (Aiello et alii, 2001). Magnetic anomaly fields have been also correlated with morphostructural features and volcanic edifices, recognized on high resolution seismic profiles recorded along the same navigation lines. Two main belts of sharp magnetic anomalies have been identified, the first located offshore the Somma-Vesuvius volcanic complex and the second offshore the Phlegrean Field volcanic complex (Siniscalchi et alii, 2002). The latter is here interpreted as the seaward boundary of the Phlegrean caldera (Orsi et alii, 2002). The detailed interpretation of the magnetic anomaly field and related seismic structures offshore the Somma-Vesuvius volcanic complex suggests a NNW-SSE structural alignment, not mentioned by previous authors, suggesting NE-SW trending normal faults (Bernabini et alii, 1973; Finetti & Morelli, 1973; Cassano & La Torre, 1987). At the same time, the detailed interpretation of magnetic anomaly fields offshore the Phlegrean Fields volcanic complex shows several complex E-W and NE-SW trending anomalies, whose values could be related to small buried volcanic features; moreover, the shape of the magnetic anomalies is not directly related to the submarine topography of large volcanic banks, revealed by Multibeam bathymetry (Aiello et alii, 2001).

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