In January 11th 1693 an earthquake, commonly reported as the
largest Italian seismic event (Io = X/XI MCS and Mw 7.4 according to
CPTI04 reference catalogue), occurred in eastern Sicily, causing more
than 54.000 casualties and totally destruction in the areas embracing
the nowadays provinces of Catania, Siracusa and Ragusa. The entire
Sicily Ionian coast was hit by a tsunami, with waves up to 8 metres
high. Several geological sources differing in location, attitude and kinematics
have been proposed by different authors for this earthquake:
the NNW-SSE Malta Escarpment normal fault located offshore the
eastern coast of Sicily, the nearly N-S Scicli strike-slip fault located in
the central Hyblean plateau, the WSW-ENE Scordia-Lentini graben in
the northern Hyblean region, the NW-dipping Ionian subduction
plane, and lastly the NNW-dipping Sicilian Basal Thrust across the
central-eastern Sicily and the Ionian offshore.
In this paper, we attempt to discriminate among the above sources
by applying a forward modelling technique which, starting from given
fault model parameters (strike, dip, length, width, hypocentral location
and magnitude) and reproducing acceleration time history above 1 Hz
(the range of frequencies correlated with building damage), calculates
the data point intensities at the surface. The differences between the
observed and calculated macroseismic intensities, expressed as L1
norm, are discussed in order to identify the better analytical solutions.
The obtained results are strongly dependent from the equivalent
magnitude (Mw) attributed to the 1693 event, which in the literature
ranges from Mw 6.8 to 8.0. Almost all the analysed fault models fall to
reproduce the highest intensity (X/XI MCS) data points of the Hyblean
region, suggesting that this area might have undergone a cumulative
damage effects due to an intense foreshock activity (January 9th 1693,
Mw 6.2, and January 11th 1693, morning, Mw 4.3). The portion of the
macroseismic field located north of the Gela-Catania thrust front is
better reproduced by the Malta Escarpment solution (Mw 7.1) and subordinately
by the Sicilian Basal Thrust and by the Scordia-Lentini
graben source models. The Hyblean portion of the field is better reproduced
by the Ionian Subduction Plane (Mw 8) and subordinately by
the Scicli line (Mw 7.4 and 7.1) source models. The entire field is better
reproduced by the Scicli line related sources (Mw 7.1 and 7.4).
Regional scale geological and seismotectonic considerations may help
to further discriminate among the various sources