Procedures for a qualitative assessment of the seismic vulnerability of historical centres. The case study of Acireale (CT)

The paper illustrates a procedure to develop a qualitative assessment of the seismic vulnerability by the application to the case study of Acireale (CT) historic centre, located on the east coast, on a lava plateau about 150 m a.s.l.. The procedure was developed within the study carried out for the historical centre of Faenza (RA) – coordinated by prof. Caterina F. Carocci (DICAR-UNICT) – and it is based on direct knowledge of the current features of the urban fabric and aims at detecting all the factors affecting, negatively (weaknesses) or positively (strengths), the seismic behaviour of masonry aggregates. The analysis is carried out in three steps. The first step, extended to the whole historic centre, involves (i) the identification of the blocks – that is a portion of urban fabric defined by public streets; (ii) the identification of a block as a case study which is representative of recurring features (i.e. site morphology, building typologies, etc.). The tools used in this phase are official maps provided by Municipality of Acireale, aerial views, and threedimensional views available on line. Secondly, for the case study, the direct survey is carried out – mainly from the outside – to collect in thematic maps information regarding the definition of building aggregates (verification of the relationship between contiguous buildings) and regarding the weaknesses and strengths associated with the following aspects: (1) relationship with the site, (2) building typologies, (3) constructive technique, (4) transformations. Finally, the critical interpretation of that information allows the identification of the recurring weaknesses that characterized the historical urban fabric, providing a qualitative assessment of the susceptibility to damage by an earthquake. A concluding note highlights how the outcomes of the qualitative evaluation of seismic vulnerability represent a useful tool for the identification of strategies for the preventative mitigation of seismic risk of the historic centre.