Site selection for creepmeter fault monitoring in a complex volcano- tectonic framework: the Mt. Etna eastern flank as an example

Mt. Etna is one of the most active volcanoes representing an exceptional natural laboratory for in-depth studies on volcano-tectonic processes. The volcano is well monitored by the INGV-OE seismic and geodetic network onshore given the high population density along its slopes, which have been affected not only by volcanic eruptions but also by damaging earthquakes. Seismicity is higher in the eastern slope which is also affected by slow gravitational sliding toward the sea with an active deformation also offshore. Flank instability is accommodated by fault systems characterized by seismic and aseismic segments with normal and strike-slip kinematics, and bounded to the N by the Pernicana Fault and to the S by the Tremestieri-Trecastagni-Aci Trezza Faults. The Trecastagni Fault is monitored by two extensometers held by INGV-OE, while offshore monitoring has been recently improved with five GEOMAR transponders along the Aci Trezza Fault offshore extension. Dyke intrusions on Etna can cause stress variations along faults triggering earthquakes and fank instability; moreover, fault creep events can follow or precede earthquakes. This pattern of interacting phenomena demonstrates how changes in the stress regime trigger seismic and aseismic transients on different faults and also causes eruptions probably related to significant extensional regime in the crust. Thus, it is important to improve the actual monitoring system with creepmeters providing time series of displacement across active faults with continuous and high-resolution measurements (1 µm). In this work we provide the first results of the geological and geophysical investigations in the Etna eastern flank and we present the methodology to characterize best suited sites, currently in progress, for future installation