Historical cities and earthquakes: Florence during the last nine centuries and evaluations of seismic hazard

Abstract

The authors' aim in the following study is to contribute to the assessment of the seismic hazard of historical cities. From this preliminary analysis the general characteristics of the seismicity affecting Florence and the evaluation of its seismic hazard may be deduced. Florence is a <<mythical>> city of world tourism, and its extraordinary artistic value and its ability to be utilized constitute a great economic resource. From this perspective, the authors have tackled some aspects of its urban features (demography and main building types, successive phases in the growth of the city, etc.), aimed at the pooling of information as a basis for further, more specific analyses of seismic risk. The study is based on a review of 131 seismic events of potential interest for the site of Florence from the 12th century. In the case of each of these earthquakes, it was possible to verify the real seismic effects sustained, and thus to assess the seismic intensity on the site. This also enabled the limits in the application of the standard attenuation laws of to be checked. Of all the earthquakes analyzed. those which caused the greatest effects on the urban area have also been identified: namely, the earthquake of 28 September 1453. and those of 18 May and 6 June 1895, both with Io=VIII MCS. From their overall analysis the authors have further extrapolated the necessary data to statistically evaluate the probabilities of any future earthquake occurring, according to intensity classes.