Abstract
A ground magnetic study was performed on the northern upper flank of Mt. Etna to provide new insights into subsurface volcano-tectonic structures. The high resolution magnetic survey was focused on the main structures of Piano delle Concazze, a large flat area dominated by the North- East crater and bounded by the rim of the Valle del Leone depression and the extremity of the North- East Rift. More than 2,500 measurements were gathered with a sampling step of about 3 m covering an area of about 0.2 km2. The total-intensity anomaly field shows the presence of intense South- North aligned maxima related to shallow geological structures affecting this area. Filtering techniques and 2.5D modeling have been applied for the determination of the magnetic source parameters. In order to distinguish the near surface structure, filters of the vertical derivatives, Butterworth high-pass and the tilt derivative were used. The 3D Euler deconvolution has been applied to estimate the depth and the structural indices of the causative sources. The calculated structural indices, that express the geometrical nature of the source, are in agreement with forward modeling. They show that the area is mainly affected by subvertical normal fault and the estimated depth of magnetic sources ranges between 10 m and 40 m. Our total field magnetic survey shows that characteristic magnetic anomalies are related to fault zones in the Piano delle Concazze that are well consistent with the local tectonics. The subsurface structures that have been detected allowed to delineate the general structural framework of the area. In particular, it was possible to clarify that these structures seem to be not deep rooted and consequently they can hardly act as preferential pathways for magma ascent.
Highlights
The dynamics of active volcanoes, is closely related to local and regional structures that are not often exposed
Considering that the vertical derivative (VDR) is potentially less sensitive to noise in the data than higher order derivatives, these last have been disregarded and only the VDR was calculated for the magnetic reduction to the pole transformation (RTP) data of the Piano delle Concazze (PDC) area (Figure 5a)
To put constraints on the geometry of the sources responsible for the main magnetic anomalies of the PDC area, a forward modeling approach was used by means of the interactive software Potent v3.06. 2.5D modeling was carried out along two East-West profiles, (AA' and BB') selected taking into account the main anomalies displayed on the magnetic anomaly grid and crossing the main faults
Summary
The dynamics of active volcanoes, is closely related to local and regional structures (faults, rift, intrusions) that are not often exposed. Even if the main structures are recorded in the general geological maps, their exact course is often debatable because their field evidence is obscured by lava flows, pyroclastic rocks and ash produced by the more recent eruptive activity and by strong erosion In these cases, geophysical surveys can give additional evidences [Barberi et al, 2004; Schrott and Sass, 2008; Blaikie et al, 2014], and among them, the magnetic investigation has been widely and efficaciously used in detecting concealed and subsurface volcano-tectonic structures. Etna and in particular for PDC, that, despite being deserted, is among the most popular tourist destination and is usually frequented by researchers, which taking advantage of the Pizzi Deneri Observatory facility, nearby located, carry out monitoring activity and advance research experiments throughout the year In this area, the main structural features of the northern flank intersect each other producing a complex dissected geological framework where particular attention should be paid to the fault systems, that can be activated by magma intrusions. The high resolution ground magnetic survey, carried out in the autumn of 2018, was aimed to identify and separate by discrete Fourier-transform algorithms the shallow and deep-seated faults, affecting this area. 3D Euler deconvolution and 2.5D modeling, were applied to estimate their depths and to better define their geometry and spatial distribution and to elucidate the relationships between them
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