GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 25 shaking rather than a real representation of the damage scenario. The recent experience of the 2016-17 seismic sequence in Central Italy proved the importance of this aspect as well as that resulting macroseismic parameters (epicentre, magnitude) are strongly inconsistent with the instrumental ones. Here we propose a reappraisal, in terms of macroseismic analysis, of the 1968 Valle del Belìce earthquakes following the same rationale. The main steps are: (i) re-analysis of primary sources to reconstruct the evolution of damage scenario during the sequence, (ii) intensity assessment, (iii) determination of the macroseismic parameters. For this last point, we propose a procedure for minimizing the magnitude overestimation to be applied in case of seismic sequences, based on “unpacking” the total seismic moment M 0 . Methodological approach. To follow the evolution of damage for as many as possible of shocks and localities, we performed a retrospective analysis of the primary sources with the purpose of simulating a-posteriori survey carried out day-by-day. To this goal, we used a wide spectrum of sources: coeval scientific papers, technical reports, macroseismic questionnaires, archive documents, socio-anthropological and architectural books, local diaries, and newspapers. The approach can be summarised as follows: (i) unpacking information referred to each single town or village, classifying data day by day and integrating information from different sources; (ii) evaluating the coherence of information; (iii) reconstructing the evolution of damage scenario during the sequence; (iv) assessing intensity and, (v) calculating earthquake parameters. The 1968 sequence may represent a stimulating laboratory also for applying the European Macroseismic Scale (hereinafter EMS-98, Grünthal, 1998). In fact, the building features can be Fig. 1 - Location of the 1968 Valle del Belìce earthquakes according to the CPTI15 earthquake catalogue (Rovida et al. , 2016).