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Two high-resolution aeromagnetic surveys three years apart were conducted to better understand the shallow subsurface structure of the Vulcano and Lipari volcanic complex, Aeolian Islands, southern Italy and monitor the volcanic activity of the area. The surveys were flown by helicopter at a mean altitude of 150 m above the terrain with NW-SE flight lines spaced about 250 m apart. In this kind of survey, however, the actual flight altitude varies, and the reduction of observed data to a smoothed surface is required to represent accurate magnetic anomalies. The equivalent source technique was employed for this purpose. A comparison between datasets at two different times was conducted to monitor the volcanic activity of the area. The subtraction of the 1999 data from the 2002 data indicates high-frequency residuals especially in magnetically high-gradient areas on Vulcano. The differences were caused probably by spatial aliasing because of insufficient survey line spacing for these areas and by altitude error based on different positioning methods. These conditions imply that it is difficult to judge if there were meaningful changes related to volcanic activity between the two surveys. Therefore, we proceeded to compile a magnetic anomaly map based mainly on the 2002 survey data with the inclusion of some profiles from the 1999 survey to cover a larger area than the individual surveys. Total magnetic intensity anomalies on the common surface parallel to and 150 m above the smoothed terrain and sea surface were complied. The map clearly shows that high-frequency and high-amplitude magnetic anomalies are distributed mainly on Vulcano, suggesting surface and shallow subsurface distributions of mafic volcanic rocks. On the other hand, no apparent magnetic anomalies lie on the southern Lipari, indicating that the area is composed of more felsic volcanic rocks than Vulcano. Furthermore, apparent magnetization intensity mapping was applied to terrain-corrected magnetic anomalies, and a reduction to the pole anomaly map was also calculated at the same time. By comparison with a geologic map, the reduction to the pole anomaly map showed local magnetic highs in the Piano district, southern Vulcano, corresponding to some outcrops of trachybasaltic-trachyandesitic rocks which fill up Piano Caldera and lie on the flanks of Primordial Vulcano (South Vulcano). Magnetic highs are also distributed in and around Fossa Cone, northern Vulcano, corresponding to trachytic and tephritic lavas forming the cone. Local magnetic highs lie on the northern (Forgia Vecchia) and eastern slopes of the cone without surface signatures. According to the result of magnetic modeling on these magnetic highs (Okuma et al., 2006), past volcanic centers that produced thick lava accumulations in Fossa Crater are implied to be overlain by thick pyroclastic rocks in these areas. This paper focuses on the compilation of an aeromagnetic anomaly map of the study area.

High-resolution aeromagnetic anomaly map of the Vulcano-Lipari volcanic complex, Aeolian Islands, Italy