Test of Source-Parameter Inversion of the Intensities of a 54,000-Deaths Shock of the Seventeeth Century in Southeast Sicily

We inverted the macroseismic intensity data set (felt reports) of theM5.4 earthquake of 1990 in SE Sicily and retrieved source parameters that were com-patible with those obtained independently by other authors who treated instrumentalobservations. Our technique uses Voronoi polygons and our kinematic function KF.After this validation, we attempted the inversion of the macroseismic intensity dataset of one of the strongest earthquakes that has ever struck the Mediterranean basin(in 1693 in southeast Sicily; 54,000 casualties). It was possible to invert the regionalintensity patterns of these two earthquakes because their data sets are sufficientlyuncontaminated by local site responses and retain regional traces of source effects.The 1693 source, constrained by our inversion, is aNNE-oriented fault, approxi-mately 60 km long, dipping from 90to 54(80with positive error of 10, andnegative error of 26) toward ESE, 50% strike-slip and 50% dip-slip, which crossesSE Sicily from the Hyblean Plateau to the coast of the Ionian Sea, south of the cityof Catania; the nucleation is 37.08N 14.93E. This source best fits the regionaldistribution of damage observed in the field. At the limit of the negative error of thedip angle, a value of 54makes our line source, at depth, compatible with the traceof the Scicli active transcurrent fault, which is 12–14 km to the west. The retrievedsource is also compatible with the orientation of the maximum horizontal geody-namical compressive stress, confidently measured in the area, as well as with anauthoritative tectonic interpretation, independent from this study. The combined useof tessellation and of our KF model is promising for inverting intensity data sets ofpreinstrumental earthquakes.