Flank instability structure of Mt Etna inferred by a magnetotelluric survey

This paper presents a magnetotelluric (MT) survey of the unstable eastern flank of Mt Etna. We take thirty soundings along profiles oriented in the N-S and NW-SE directions, and from these data recover two 2D resistivity models of the subsurface. Both models reveal three major layers in a resistive-conductive-resistive sequence, the deepest extending to 14 km bsl. The shallow layer corresponds to the volcanic cover, and the intermediate conductive layer corresponds to underlying sediments segmented by faults. These two electrical units are cut by ~ E-W-striking faults. The third layer (basement) is interpreted as mainly pertinent to the Apennine-Maghrebian Chain associated with ~ SE-NW-striking regional faults. The detailed shapes of the resistivity profiles clearly show that the NE Rift is shallow-rooted (~0-1 km bsl), thus presumably fed by lateral dikes from the central volcano conduit. The NW-SE profile is characterized by a series of listric faults reaching up to 3 km bsl, then becoming almost horizontal. Towards the SE, the resistive basement dramatically dips (from ~3 km to ~10 km bsl), in correspondence with the Timpe Fault System. Several high-conductivity zones close to the main faults suggest the presence of hydrothermal activity and fluid circulation that could enhance flank instability. Our results provide new findings about the geometry of the unstable Etna flank and its relation to faults and subsurface structures.