The attenuation of seismic intensity in the Etna region and comparison with other Italian volcanic districts

R. Azzaro, M. S. Barbano, S. D’Amico, T. Tuvè


A detailed analysis of the intensity attenuation in the Etna and other Italian volcanic districts, was performed using
the most recent and complete intensity datasets. Attenuation laws were derived through empirical models fitting ?I
(the difference between epicentral I0 and site Ix intensities) average values versus hypocentral site distances by the
least-square method. The huge amount of data available for the Etna area allowed us to elaborate bi-linear and logarithmic
attenuation models, also taking source effects into account. Furthermore, the coefficients of the Grandori
formulation have been re-calculated to verify the ones previously defined for seismic hazard purposes. Among the
tested relationships, the logarithmic one is simple and fairly stable, so it was also adopted for the other volcanic
Italian areas. The analysis showed different attenuation trends: on the one hand, Etna and Ischia show the highest
decay of intensity (?I=4) in the first 20 km; on the contrary, the Aeolian Islands and Albani Hills present a slight
intensity attenuation (?I=2) at 20 km from the hypocentre; finally, Vesuvius seems to have an intermediate behaviour
between the two groups. The proposed regionalization gives a significantly better image of near-field
damage in volcanic regions and is easily applicable to probabilistic seismic hazard analyses.


macroseismic intensity;attenuation;Mt. Etna;Italian volcanic areas

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X