Seismic Hazard and Related Risk at Mt Etna Volcano: a contribution to the improvement of emergency plans

Nicolosi, Italy

Natural disasters, such as earthquakes and volcanic eruptions, have strong effects on the socioeconomic
well-being of countries and their people. The consequences of these events can lead to complex
cascades of related incidents, and in more serious contexts they can threaten our basic survivability. The
problem of the seismic risk is a well-known issue at Etna due to the high-intensities volcano-tectonic
earthquakes that frequently damage the very populated flanks of the volcano.
In the framework of the european UPStrat-MAFA project, seismic hazard was performed following
the probabilistic approach (PSHA) based on historical macroseismic data, by using the SASHA code
[D’Amico and Albarello, 2008]. This approach uses intensity site observations to compute the seismic
history for each investigated locality; the results, are expressed in terms of maximum intensity expected in a
given exposure time, for exceedance probability thresholds.
The seismic site histories were reconstructed from the database of macroseismic observation related to
the historical catalogue of Mt. Etna from 1832 to 2013 [CMTE, 2014], implemented by “spot” observations
as far back as 1600 [Azzaro and Castelli, 2014]. To improve the completeness of the site seismic histories,
the dataset of the observed intensities was integrated with ‘virtual’ values, calculated according to
attenuation laws. The attenuation model applied is based on Bayesian statistics performed on the Etna dataset
[Rotondi et al., 2013], and provides the probabilistic distribution of the intensity at a given site.
The hazard maps, calculated using a grid spaced 1 km, shows that for short exposure times (10 and 30
years, Figure 1a), volcano-tectonic earthquakes are the main source of shaking for the area. In particular
localities in the eastern flank of the volcano have very high probabilities to suffer damage at least of VII degree
in the next 30 years. Moreover, the de-aggregation analysis between magnitude vs seismic source demonstrates
that S. Tecla fault (STF in Figure 1b) is one of the structures that mostly contribute to the hazard.