GNGTS 2022 - Atti del 40° Convegno Nazionale

288 GNGTS 2022 Sessione 2.2 for ordinary building design, they provide additional details for the geological modelling that represents the basis for successive numerical simulations of the site response. The sites investigated on the Gargano plateau are characterized by the presence of carbonate rocks whose age ranges from Cretaceous to Eocene. Although the outcropping units consist of stiff rocks, they are locally intensely fractured (e.g., along major faults) or covered by incoherent deposits derived from the dismantling of the same rocks. The thickness of such deposits can amount up to a few tens of meters. The variability of site conditions is reflected by the presence of alternance of sites with flat HVSR curves in the range 0.9-10 Hz and sites where pronounced peaks are observed in the same range. Figure 3 shows examples from the municipality of San Marco in Lamis, whose built up area is located in a valley filled with eluvial- colluvial materials. Such setting leads to strong resonance effects at frequencies variable from 4 to 8 Hz, with a frequency increase likely associated to the thinning of the deposit. The resonances found at frequencies higher than 10 Hz reflect the presence of thinner surficial layers of softer material (e.g., soils or anthropic backfill). Where carbonate rocks crop out, the HVSR values are lower and typically below the threshold of significance for the identification of site amplification effects (commonly considered at the level of H/V = 2); moderate peaks are locally observed at frequencies around 10 Hz or higher, possibly related to the presence of surface layers of weathered/fractured rock. Fig. 3 - Geological map of the area investigated during the SM of San Marco in Lamis (FG) with few examples of the results of HVSR analysis of ambient noise data (after Pitullo, 2022). Conclusion. The ongoing Seismic Microzonation of 84 Apulian municipalities offers the opportunity to acquire a large amount of valuable data for the assessments of local seismic hazard in a region where this kind of efforts have until now been almost neglected. In this context, ambient noise analysis based on the HVSR technique allowed us to recognise a variety of litho-stratigraphic conditions that can lead to seismic ground motion amplifications. At this regard, quite different situations are encountered in the main geological domains of the Apulia region: the investigated sites in the Daunia Mountains show generally moderate resonance phenomena with short distance variations related to the diffuse presence of heterogeneous flysch materials and the absence of a shallow stiff substratum; the sites in the Tavoliere plain present strong resonance peaks at very low (< 0.9 Hz) frequencies (irrelevant