Correlation between the dynamics of the Hyblean Foreland and Etnean volcanism

The Hyblean Foreland (South Eastern Sicily) represents the northern extremity of the African Plate in collision with the Euro-Asiatic one. It is mainly made up of quite thick carbonate formations and volcanic units, which are in subduction under the Tertiary allochthonic terrains and Quaternary clays, on which the volcano Etna is formed. In the recent past, researchers have analysed both the historical and instrumental seismicity of the Hyblean Foreland as a phenomenon independent of the dynamics to which Etna is prone; in fact, it was presumed that the particular seismic style of the Hyblean area, characterised by large releases of seismic energy in a brief time span after centuries of relative quiescence, was only related to the dynamics of plate-tectonics in the Mediterranean area. The detailed analyses and the results obtained in this study, based on the instrumental seismicity of the Hyblean area between 1983 and 2002, partially modify this point of view. Although the current convergence between the African and Euro-Asiatic plates does play a significant role in the tectonic activity of south-eastern Sicily, the authors believe that the behaviour of the mantle under Mt Etna does seem to have a controlling influence on the seismicity of the area under study. In particular, on comparing the development between the eruptive activity of Etna and the seismic energy of the Hyblean Foreland in the period between 1983 and 2002, the b-value trend and the characteristics of the stress field in the period 1994–2002, the authors deduce that the rising of the mantle in the Etnean area may have disturbed the stress distribution in the Hyblean area. The modifications produced in the stress field trigger earthquakes of a higher magnitude in the areas near the volcanic one. Finally, it is hypothesised that the disastrous seismic phenomena of the last 1000 years have been set off by the interaction between the local dynamics of the mantle and the regional dynamics associated to the plate-tectonics.