An integrated magnetotelluric study of the Mt. Etna volcanic structure

Abstract

he results of a magnetotelluric (MT) survey performed at Mt. Etna (Sicily, Italy) are presented and discussed. The MT interpretation is preceded by the description of the data managing strategy used for the estimate of the impedance tensor and the computation of a rotationally invariant parameter. The 1D Bostick inversion of MT soundings located in the Etnean central area highlights the existence of a wide conductive zone in the depth range 15-30 km. Resistivities of a fewW×m are estimated in the southern part of this zone, while resistivities one order of magnitude higher are estimated in the northern part. In the central sector, the MT soundings are characterized by much higher resistivity values suggesting the presence of an E-W directed resistive barrier separating the two conductive deep zones. A two-feeding system is thus hypothesized as an extension of a previous 3D model deduced from regional earthquakes and teleseisms in the depth range 15-25 km. Moreover, the comparison with previous shallow seismic tomographies from local earthquakes within the first 11 km of depth allows us to distinguish inside the upper portion of the resistive barrier a central high velocity zone. This zone can likely be ascribed to a slowly cooled dike tending to become highly fractured at its western and eastern edges. Finally, the impedivity analysis based on the comparison with previous geoelectric dipole soundings allows us to exclude the existence of a permanent magma chamber within the first 5 km of depth and to argue the existence of a shallowplumbing system consisting of a medium-to-low temperature hydrothermally altered environment.