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 two 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 SW-NE-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 suggests by a series of
listric faults reaching up to 3 km bsl, then becoming almost horizontal. Toward 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.

This paper presents a magnetotelluric (MT) survey of the unstable eastern flank of
Mt. Etna. We take thirty soundings along two 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 SW-NE-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 suggests by a series of
listric faults reaching up to 3 km bsl, then becoming almost horizontal. Toward 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.

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