GNGTS 2022 - Atti del 40° Convegno Nazionale

116 GNGTS 2022 Sessione 1.2 provide a possible link to the larger scale tectonic framework, a campaign of multi-technique geophysical surveys has been carried out in April 2022. It involved electrical resistivity measurements, thermography, gravimetric and magnetic surveys; this paper presents the preliminary results of the magnetic survey (Fig. 1). In fact, magnetometry has been widely used to detect faults, or geological discontinuity in general, in volcanic contexts and at various scales (Bottari et al. , 2018, Napoli et al. , 2020). Data and method. The magnetic survey was performed with the device G-858G produced by Geometrics Inc. The magnetometer was set in gradiometric configuration with the two sensors 2.0 m apart. The magnetometer is equipped with a GPS that provide the position and the time for each magnetic measure, taken every 0.5 s. The survey consists of more than 14,000 measurements taken along different tracks of total length equal to 6.6 km; the average spacing between two consecutive measures is about 0.5 m. The data processing consists in the spikes removal and in a running average over 40 samples acting as a low-pass filter. The filter attenuates, the shorter wavelength component related to the shallower anomalies, enhancing the components with larger wavelength. The investigated area extends at the southwestern base of the cone named “La Fossa” which is the active crater located within the caldera of Vulcano Island. In particular, the survey was focused in the area where the seismic investigation by Bruno and Castiello (2009) shows a velocity anomaly interpreted as a possible fault zone. In this area we performed back-and- forward profiles. Data, reduced with respect the International Geomagnetic Reference Field (IGRF), have been interpolated by kriging on a 5x5 m grid. Fig. 2 - Maps of the total magnetic anomaly field (left) and of the vertical gradient (right). Elevation lines are 25 m spaced. Results. The total-field magnetic anomaly map and the vertical gradient map are presented in Fig. 2. The total field is generally characterized by negative values. This is in agreement with the observations from other magnetic surveys (airborne, shipborne or ground-based) carried out at Vulcano Island (Supper et al. , 2004; De Ritis et al. , 2005; Okuma et al. , 2006; Blanco- Montenegro et al. , 2007; Napoli and Currenti, 2016). Those extend over the whole island but are at lower resolution. The total magnetic field shows an almost regular increase in the values moving upslope towards the cone (i.e. SW-NE direction). This can be interpreted with the