Dynamic analysis of a seismically induced mass movement after the December 2018 Etna volcano eruption

On December 24, 2018, Etna volcano began a very intense eruption, featuring massive ash and gas emissions, lava flows, and a seismic swarm with magnitudes less than . Hundreds of earthquakes (Fig. 1) were associated with a dyke intrusion in the upper part of the Etna volcano, which induced significant deformation of the volcanic edifice (Bonforte et al., 2019; De Novellis et 11 al., 2019). The dyke intrusion encouraged, with favourable stress loading, seismic dislocation of the Fiandaca Fault (Fig. 1) (De Novellis et al., 2019). A strike-slip earthquake (Mw 4.9) nucleated on December 26, 2018, at a focal depth of approximately 1 km, causing ground fractures and seismic shaking with PGA up to 0.075g, which caused some damage to nearby villages (Villani et al., 2020). Space-borne synthetic aperture radar (SAR) data from Sentinel-1 (hereinafter S-1) provided a stunning picture of the displacement fields caused by volcanic eruption and earthquake dislocation Bignami et al., 2019; Bonforte et al., 2019; De Novellis et al., 2019). Fig. 1a shows the wrapped displacement observed in the period December 22-28, 2018 along the descending line of sight (LoS), that is the direction of the shortest path between a point on the Earth’s surface and the SAR antenna. One highly visible deformation pattern is located along Mt. Etna's flanks, where a bi-lobate interferometric fringe pattern highlights the deformation induced by dyke intrusion (Bonforte et al., 2019; De Novellis et al., 2019). A second deformation pattern is localised to the S-E of Etna volcano, where small fringe pattern identifies the displacements caused by the December, Mw 4.9 strike- slip dislocation of the Fiandaca Fault (De Novellis et al., 2019). Local small interferometric fringes identify a third deformation pattern over a hilly area located approximately 5 km west of Paternò village (the dashed black box in Fig. 1a) (Bignami et al., 2019). This displacement is not related to volcanic inflation or fault dislocation, because no large earthquakes have occurred nearby. The unwrapped S-1 interferograms (Fig. 1b) show that displacements reach approximately 6 cm at the foot of the hill along both the descending and ascending orbits and gradually vanish towards the boundaries of the DGSD. The similarity of displacement amplitudes and spatial extents along satellite trajectories with different signs (negative and positive displacements indicate movements away from and towards the satellite sensor, respectively) suggest that horizontal displacements dominate the actual movement. Bignami et al. (2019) interpreted this displacement as potentially associated with the seismic reactivation of a paleo-landslide.