First studies of probabilistic seismic hazard assessment in the volcanic region of Mt. Etna (southern Italy) by means of macroseismic intensities

Results of probabilistic seismic hazard assessment (PSHA), in terms of macroseismic
intensity applied to the Mt. Etna region, are presented. PSHA has been performed using
a numerical procedure based on the extensive use of local macroseismic information, as
an alternative to the usual Cornell-McGuire methods. The large amount of intensity data
available for this area - coming from the Italian intensity database DBMI04 for the
regional earthquakes, and from the Etna catalogue for the ‘local’ events - has provided
fairly exhaustive seismic site histories (i.e. the data set of macroseismic observations
available for a given locality) to estimate the seismic hazard for 402 localities on the
volcano. In order to improve the completeness of the site catalogue when historical
information is missing, observed intensity data have been integrated with values
calculated from epicentral information obtained by using an attenuation law specific for
the Etna region. Using a probability distribution considering the completeness of the input
database and the uncertainty of intensity data, the hazard in terms of maximum intensity
(Iexp) characterised by a 10% probability of exceedance in an exposure time of 50 years,
has been computed. The highest values ( Iexp = IX or X) are found in the south-eastern
flank of Mt. Etna while the rest of the volcano is exposed to a lower hazard (Iexp = VIII).
Despite the low energy (M≤4.8) compared with that of the large regional earthquakes
affecting the area (6.6≤M≤7.4), the local events strongly influence the pattern of the
hazard in the eastern sector of Mt. Etna, representing a significant, and sole, source of
hazard when a shorter exposure time (e.g. 30 years) is considered.

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