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Magmatic intrusions, eruptions and flank collapses are frequent processes of volcano dynamics, inter-connected at different space and time scales. The December 2018 recrudescent episode at Mt. Etna is an exemplary case where a sudden intrusive event culminated with a short eruption, intense seismicity and a shallow large strike-slip earthquake at the edge of the eastern sliding flank. Here, we show that high resolution velocity models and transient changes of VP and VP/VS resolve the magma intrusion through a dyke and local stress increase at the base of the unstable flank, inducing the collapse. Episodic brittle faulting occurs at the edge of the sliding sector, locally contributed by high fluid pressure. The feedback between magma ascent, stress changes and flank collapse is driving the volcano dynamics, with processes ranging from long term to transient episodes. [ABSTRACT FROM AUTHOR]

The mechanism of seismic attenuation for shear waves was studied through the separate measure of the intrinsic dissipation and scattering coefficients. A modified version of the Multiple Lapse Time Window Analysis (MLTWA) was applied to about 5000 local earthquakes with magnitude 1.5 ≤ Ml ≤ 4.8 occurred in the period 2006–2017 in both the tectonic (Peloritani Mountains and Hyblean Plateau) and volcanic (Aeolian Islands and Mt Etna) areas of eastern Sicily. Observed data, processed via direct Fourier Transform instead of the filtering and averaging procedures utilized in the ordinary MLTWA technique, were fit to the correspondent Paasschens solution of the Energy Transport model in 3D. Model parameters B 0, the seismic albedo, and Le , the extinction length, in turn associated with the intrinsic (Qi) and scattering (Qs) quality factors for S waves, are thus obtained from the fit in the frequency bands centred at 1.5, 3, 6 and 12 Hz. Finally, the corrections to these estimates in case of an opaque layer (the crust) overlying a uniform and transparent mantle, were applied in order to obtain more realistic estimates of the seismic attenuation in the areas investigated. Obtained results are first interpreted in terms of the characteristics of each domain and then compared by the same point of view with a huge set of measurements of the same parameters carried out in other tectonic and volcanic domains through the world. Results show how the rock heterogeneity characterizes the tectonic domain and determines the value of total attenuation coefficient, which, on the other hand, is a crucial parameter in the estimation of the seismic hazard. [ABSTRACT FROM AUTHOR]

Seismic wave attenuation in southeastern Sicily was investigated by using a data set of about 180 local earthquakes recorded in the period 1994–2003. We first estimated the quality factor of S waves and clarified its frequency dependence by means of the coda-normalization method, applied in the frequency range 1.5–15 Hz. The average as function of frequency is given by . A detailed separation of scattering attenuation from intrinsic absorption was also attempted by applying the multiple lapse time window analysis (MLTWA), under the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Intrinsic absorption dominates over scattering in the attenuation process at high frequencies (above 3 Hz). Below 3 Hz scattering is the predominant attenuation effect in the region, at the scale length of these frequencies. However, some discrepancies have been observed between the theoretical model and the observations. This indicates that models with depth-dependent velocity structure and/or non isotropic scattering should be taken into account in order to remove ambiguities in the interpretation of the results. [ABSTRACT FROM AUTHOR]