Test of source-parameter inversion of the intensities of a 54,000-death shock of the seventeenth century in Southeast Sicily

We inverted the macroseismic intensity data set (felt reports) of the M 5.4 earthquake of 1990 in SE Sicily and retrieved source parameters that were compatible with those obtained independently by other authors who treated i nstrumental observations. Our technique uses Voronoi polygons and our kinem atic function KF. After this validation, we attempted the inversion of the macroseismic intensity data set of one of the strongest earthquakes that ha s ever struck the Mediterranean basin (in 1693 in southeast Sicily; 54,000 casualties). It was possible to invert the regional intensity patterns of t hese two earthquakes because their data sets are sufficiently uncontaminate d by local site responses and retain regional traces of source effects. The 1693 source, constrained by our inversion, is a NNE-oriented fault, approx imately 60 km long, dipping from 9 degrees to 54 degrees (80 degrees with p ositive error of 10 degrees, and negative error of 26 degrees) toward ESE, 50% strike-slip and 50% dip-slip, which crosses SE Sicily from the Hyblean Plateau to the coast of the Ionian Sea, south of the city of Catania; the n ucleation is 37.08 degrees N 14.93 degrees E. This source best fits the reg ional distribution of damage observed in the field. At the limit of the neg ative error of the dip angle, a value of 54 degrees makes our line source, at depth, compatible with the trace of the Scicli active transcurrent fault , which is 12-14 km to the west. The retrieved source is also compatible wi th the orientation of the maximum horizontal geodynamical compressive stres s, confidently measured in the area, as well as with an authoritative tecto nic interpretation, independent from this study. The combined use of tessel lation and of our KF model is promising for inverting intensity data sets o f preinstrumental earthquakes.