A systematic analysis at stations of the Italian seismic network to test the role of local topographic effect.

The Italian seismic code (NTC18) provides indications about the expected effects of some morphological configurations on the expected ground motion during earthquakes. In particular, two main 2D morphologies are identified as reference: cliffs and crests. Based on numerical simulations, the value of St is assumed to depend on the steepness of the cliffs and aspect ratio of the crest. A critical aspect of these estimates is that the considered configurations are defined in terms of steepness angles and aspect ratios, without any scale indication. Moreover, the considered morphologies are very schematic, and this prevents their simple application in the natural context: in most case an expert judgement is necessary, and this makes the final estimates potentially controversial and difficult to validate on the basis of empirical observations. To face this problem, in the frame of the PRIN project “SERENA”, a procedure has been developed for the automatic identification of areas prone to morphological amplification effects by following NTC18 prescriptions,  based on the Digital Terrain Model. The proposed approach allows the full exploitation of topographical data at the maximum resolution available. After a first application to restricted areas, the proposed procedure has been applied at National scale at the seismometric and accelerometric sites managed by INGV. The aim is twofold: first comparing outcomes of the new approach with the ones proposed by other Authors at the same sites, second to provide a sound basis of a coherent and reproducible estimate of St values to be compared with possible empirical evidence. In the presentation, the results obtained about the first aim will be presented and discussed.