GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.3 167 THE MT. ETNA 2018 FLANK ERUPTION: SEISMOLOGICAL INVESTIGATIONS AND NEW INSIGHTS ON THE VOLCANO FLANKS DYNAMICS S. Alparone, G. Barberi, E. Giampiccolo, V. Maiolino, A. Mostaccio, C. Musumeci, A. Scaltrito, L. Scarfì, T. Tuvè, A. Ursino Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania, Osservatorio Etneo, Italy Introduction. On December 24, 2018 an intense seismic sequence, starting at 08:30 UTC, preceded and accompanied the beginning of a flank eruption at Mt. Etna volcano, about ten years after the last 2008-2009 flank eruption. Simultaneously, a strong increase in the volcanic tremor amplitude was recorded. The seismicity associated with the eruption (December 24-25, 2018) took place mainly during the first 24 hours. It accompanied the intrusion of a magmatic dyke and the opening of the eruptive fracture in the summit area. The main evidences that came out from the analysis of the space-time distribution of the seismicity reveal that the first cluster of events was located beneath the summit craters and along the eruptive fracture with epicentres aligned in a N-S direction. Then, seismicity migrated towards south and southeast, as a probable response of the medium to the incoming intrusion. Following, the bulk of seismicity moved towards the western wall of the Valle del Bove (VdB), in concomitance with the increase in the volcanic tremor amplitude. The seismicity which followed the main eruptive episode (December 26, 2018-February 28, 2019) affected the eastern and southwestern flanks of the volcano. The most energetic event (M L =4.8), recorded on December 26 at 02:19 UTC, was located just below the sea level in the middle eastern flank of the volcano, along the Fiandaca- Pennisi Fault (FPF), a seismogenic structure belonging to the Timpe Fault System (TFS). Following December 26, the seismic sequence decreases dramatically in terms of daily events and magnitude. On January 8, at 23:50 UTC, a M L =4.1 earthquake occurred in the northern sector of the volcano, along the Pernicana Fault System (PFS), one of the most active and well- Fig. 1 - Map and W-E cross sections of the 3D locations of earthquakes (M L ≥1.1) located (a) before (October 2017-December 23, 2018), (b) during (December 24-25, 2018) and (c) after the period of particularly intense eruptive activity (December 26, 2018-February 28, 2019). Different colors are used to indicate an upper crustal (<10 km) and a lower crustal (≥10 km) hypocentral depth. Yellow stars mark the location of the seismic events with M L ≥4.0. Simplified tectonic structures are from Neri et al. (2009). FPF: Fiandaca-Pennisi Fault; TFS: Timpe Faults System; PFS: Pernicana Fault System; RFS: Ragalna Fault System.