Ground-motion scenarios on Mt. Etna inferred from empirical relations and synthetic simulations

Abstract

Ground motion scenarios for Mt. Etna are created using synthetic simulations with the program EXSIM. A large data set of weak motion records is exploited to identify important input parameters which govern the modeling of wave propagation effects, such as Q-values, high frequency cut-off and geometrical spreading. These parameters are used in the simulation of ground motion for earthquakes causing severe damage in the area. Two seismotectonic regimes are distinguished. Volcano-tectonic events, though being of limited magnitude (M max ca. 5), cause strong ground shaking for their shallow foci. Being rather frequent, these events represent a considerable threat to cities and villages on the flanks of the volcano. A second regime is related to earthquakes with foci in the crust, at depths of 10-30 km, and magnitudes ranging from 6 to 7. In our synthetic scenarios, we chose two examples of volcano-tectonic events, i.e. the October 29, 2002, Bongiardo event (I = VIII) and the May 8, 1914, Linera earthquake (I = IX-X). A further scenario regards the February 20, 1818 event, considered representative for stronger earthquakes with foci in the crust. We were able to reproduce the essential features of the macroseismic field, in particular accounting for the possibility of strong site effects. We learned that stress drop estimated for weak motion events is probably too low to explain the intensity of ground motion during stronger earthquakes. This corresponds to findings reported in the literature claiming an increase of stress drop with earthquake size.

Intrusive Seismic Swarms as Possible Precursors of Destructive Earthquakes on Mt. Etna’s Eastern Flank

“…The 2002 October 29 earthquake, with a magnitude of Ml = 4:5, caused heavy damage even to reinforced concrete structures in the epicentral area, along a narrow but elongated zone (over 4 km in length) where the macroseismic intensity reached degree VIII [18,25].…”

Applying Simulated Seismic Damage Scenarios in the Volcanic Region of Mount Etna (Sicily): A Case-Study From the MW 4.9, 2018 Earthquake

“…While the estimation of damage to residential buildings is a consolidated practice for "tectonic" earthquakes, its application on volcanoes requires ad-hoc approaches taking into account the characteristics of local seismicity, such as the small-moderate magnitude (M max ∼5.3), the shallow depth of sources (<3 km), the high values of peak ground motion (PGM) parameters and the low-frequency content in the near field, and the strong attenuation of intensity in very short distances (Azzaro et al, 2006(Azzaro et al, , 2017Langer et al, 2016;Iervolino, 2018;Tusa et al, 2020). The main feature of the earthquake seismic scenarios at Etna is that the involved areas are relatively small (∼30 km 2 ) and characterized by a large variability of effects in a few kilometers (QUEST Working Group, 2019).…”