GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 2.2 337 different damage levels and local site response of the soils where the structures lay. Analysis and results. The map of the observed damage (Fig. 1) shows that the inhabited centres most affected by the event are in the area of VI MCS degree, at different distances from the epicenter and located on loose deposits. This is the case, for example, of the centres located in the municipalities of Piedimonte Matese and Faicchio. This result seems to suggest that the damage distribution originated from ground motion amplification effects both at large-scale and small-scale, and from the structural typology of the buildings. While large-scale site effects can be ascribed to the contact between soil deposits (e.g., clastic and alluvium deposits,…) and the limestone characterizing the Matese massif, the small-scale effects can be due to the fact the buildings foundations lay on alluvial fan and debris. To test this hypothesis, we have selected two edifices that present large damage (Fig. 2). For both of them we have computed the structural response and the transfer function of the soil where they are located. We have performed the H/V ratio analysis using seismic noise recorded at the ground flour and the top flour of the considered edifices (Nigro et al. , 2015). From the comparison of the observed dominant frequencies resulting from the H/V ratios (Fig. 3) and those obtained from a model of the buildings, two clear points arise: the first dominant frequencies indicated with 1 in Fig. 3, are ascribed to the local seismic response, whereas the frequencies of the second peak, indicated with 2 in Fig. 3, are the frequencies related to the structural oscillations of buildings. Note that, the dominant frequencies of the soils range between 1-2 Hz, which is very close to the corner frequency of the seismic event (Convertito et al. , 2016), whereas those of the buildings, taking into account for all the uncertainties, range Fig. 2 - a) Picture of the damage affecting building B and b) those affecting building D. Fig. 3 - H/V ratio analysis of the two buildings shown in Fig. 2 and the correspondent site response functions.