Neo-deterministic seismic hazard scenarios: Application to the engineering analysis of historical buildings.

An integrated neo-deterministic approach to seismic hazard assessment has been developed that combines different pattern recognition techniques, designed for the space-time identification of strong earthquakes, with the procedure for the neo-deterministic assessment of seismic hazard. The integrated approach allows for a time dependent definition of the seismic input (realistic synthetic seismograms), through the routine updating of earthquake predictions. The time information given by the intermediate-term middle-range earthquake prediction can be used to enhance and optimize preparedness actions. Accordingly, when an alarm is declared, ground shaking scenarios at bedrock can be readily computed for the entire alerted area, as well as for the individual areas prone to strong earthquakes included in it, thus providing a reliable and reproducible picture of what should be expected when a strong earthquake occurs. For those sites where intensity values greater than VI (MCS) are estimated at bedrock, further investigations can be performed taking into account the local soil conditions, in order to compute the seismic input (realistic synthetic seismograms) for engineering analysis of relevant structures, such as historical and strategic buildings. A pilot application of the proposed approach, including a detailed evaluation of the expected ground mo-tion accounting for site effects, has been carried out, among others, for the city of Trieste. Attention has been focused on Palazzo Carciotti, a masonry neoclassical palace, which has a prominent artistic relevance within the city. The palace is located in the ancient part of Trieste, where soft superficial sediments of poor geotech-nical characteristics are present. Ground motion modeling shows that these site conditions may lead to a peak ground acceleration value of 0.2 g, greater than the value obtained at bedrock. The computed synthetic seis-mograms have been used as seismic input for the engineering seismic safety appraisal of the building. Three kind of dynamic analysis have been carried out: a) a modal analysis, using response spectrums calculated both from synthetic seismograms and according to Eurocode 8, b) a push-over analysis, c) a dynamic push-over analysis, which have evidenced that a strong earthquake (M=6.5) occurring in the proximity of Trieste (21 km far from the considered site) could seriously compromise the stability of the structure. The realistic computation of the seismic input, taking in account the local soil conditions, combined with the evaluation of the seismic response of buildings provides an effective approach to the assessment seismic risk.