Contribution of tsunami data analysis to constrain the seismic source: The case of the 1693 Eastern Sicily earthquake

The January 11, 1693 eastern Sicily earthquake is comparable only with the December 28, 1908 Messina Straits event in the Italian seismic history as regards magnitude (ML ≅ 7), level of destruction and number of victims. The shock generated a strong tsunami, which hit the entire eastern coast of Sicily and particularly the town of Augusta. The problem of which fault was responsible for the earthquake is still open. Several hypotheses have been formulated in the literature on the basis of different kinds of geological, macroseismic and tectonic data, but a general agreement has not been reached yet. An important contribution to the discussion may come from the analysis of the tsunami data. In two previous papers (Piatanesi et al., 1996; Piatanesi and Tinti, 1998), the hydro-dynamical study of the tsunami based on finite-element (FE) numerical simulations was carried out taking into consideration mostly theoretical faults, i.e. faults selected for their significance in tsunami generation irrespective of the corresponding geological evidence. This paper has to be considered the continuation of the mentioned works. We have studied new sources proposed in the literature, consistent with macroseismic data and/or geological observations, and simulated the corresponding tsunamis. We also built a new FE grid introducing significant improvements in the coastline representation, and developed and applied a new algorithm in order to account for the effect of the sea-bottom topography on the tsunami initial condition. Some of the examined faults are located in the Scordia-Lentini (SL) graben region and intercept the coastline, others are placed in correspondence with the Hyblaean-Malta (HM) escarpment and run parallel or sub-parallel to the coast. The conclusion of our work is that none of these faults respects fully the available observations on tsunami, and that the faults exhibiting the best fit are those placed in the SL region. It is worth stressing that our results are important for the assessment of seismic and tsunami hazard/risk in eastern Sicily, keeping also in mind that the 1693 earthquake has been selected as the reference event for an earthquake-scenario study in Catania and in south-eastern Sicily, called 'Catania Project', funded by CNR/GNDT (Consiglio Nazionale delle Ricerche/Gruppo Nazionale Difesa dai Terremoti).