GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 11 microseismicity and to the insufficient constraint of the seismic sources, could represent a limit of the current seismological knowledge in this volcano sector. The Trecastagni Fault (TF) is a discontinuity that develops in the southern flank of Mt. Etna, between the Trecastagni and San Giovanni la Punta villages. This is an active structure with an approximately NNW-SSE trend (Fig.1a) characterized by morphological escarpments. The seismicity of the TF is characterized by very shallow earthquakes with typical focal depths of 1-2 km below sea level. Also south of TF creep effects are visible along the San Gregorio di Catania fault (Imposa et al. , 2015). Evident co-seismic surface faulting occurred along the fault scarp of TF in September 1980 and in November 1988 (Azzaro, 1999). Hollows appeared in agricultural land and fractures in buildings, boundary walls and the road 8/III, were observed after the local shocks on September 16 and 20, 1980 and also after the 21 November 1988 earthquake (Azzaro, 1999). Other similar episodes on 26 May 1903, 20 July 1917 and 17 February 1955, have been reconstructed by historical research (Azzaro and D’Amico, 2008). In recent years, some minor shallow earthquakes have been felt by the local residents; in particular, on 15 October 2009, at 00:52 GMT, M=2.1 and on 29 October 2010, at 01:37, M=2.2. (Gambino et al. , 2011). Fig. 1 - (a) Schematic tectonic framework of Mt. Etna volcano (Barreca et al. , 2013); (b) Seismic stations managed by the Istituto Nazionale di Geofisica e Vulcanologia Osservatorio Etneo – Sezione di Catania (red triangles) and by the University of Catania (green triangle). Ten years after the last flank eruption of 2008-2009, on December 24, 2018 an intense seismic sequence preceded and accompanied the beginning of a flank eruption at Mt. Etna volcano. In a few days, more than 3000 earthquakes were recorded by the INGV-OE (Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Etneo) permanent seismic network, most of them in the first 24 hours. The most powerful event (ML=4.8; MW=4.9) was recorded on December 26 at 02:19 UTC and occurred just below sea level between the villages of Fleri and Pennisi. After this event, the seismicity affected the central areas of the volcano and subsequently it involved more peripheral sectors including the southern structures, in particular the Tremestieri Etneo and Trecastagni fault systems (Alparone et al. , 2009 submitted). The purpose of this paper is to study three earthquakes and their possible links with ground deformation data recorded by extensometric stations operating in this volcano sector. In particular, we integrated the seismic data of the permanent INGV-OE network with the station managed by the University of Catania and located near the fault under investigation. Monitoring network. The permanent seismic network, managed by INGV-OE, consists of about 30 stations equipped with broadband 3-component seismometers (Fig.1b). Since the geometry of this network is sparse in the southern sector of volcano, we have added a