GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 2.2 285 FIRST RESULTS OF AMBIENT NOISE DATA ANALYSIS FROM THE ONGOING SEISMIC MICROZONATION OF THE APULIA REGION V. Del Gaudio 1 , J. Wasowski 2 , C. Magrì 1 Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari “Aldo Moro”– Bari, Italy 2 Consiglio Nazionale delle Ricerche – Istituto di Ricerca per la Protezione Idrogeologica - Bari, Italy Introduction. Seismic Microzonation (SM) of Italy is ongoing according to standardised rules, with the financial support of the National Civil Protection Department and co-funded by the Regional Administrations. The main purpose is to provide the municipalities exposed to seismic risk with information needed to increase the safety level in the design of engineering structures and to optimise the urban planning provisions. One of the products expected from the SM investigations is a map of the site resonance frequencies, based on the results of acquisition and analysis of ambient noise data processed with the technique of the calculation of the horizontal-to-vertical spectral ratios (HVSR - Nakamura 1989). According to the national provisions, such a map is required at a first stage of the SM to provide information useful for earthquake resistance design and for the definition of the geological model to be used in the numerical analysis of local site response properties. Apulia present rather heterogeneous conditions in terms of distances from seismogenic zones and with regard to local geological-geomorphological conditions. Major seismogenic structures within the Apulian territory are located in its northernmost area (Foggia Province - cf. Del Gaudio et al. , 2007). However, damaging effects can derive from earthquakes occurring in the southern Apennines or in Adriatic-Ionian areas facing the Apulia coasts, especially in presence of local conditions for site amplification. There is a lack of rigorous observations on the effects of strong earthquakes in Apulia. Therefore, it is crucial to have the possibility of assessing the potential impact of future earthquakes based on a combination of detailed geological mapping, ambient noise analysis and numerical modelling. The present study reports the first outcomes derived from the implementation of systematic ambient noise analysis in Apulia within the SM investigations in progress. Geological Context. The Apulian territory extends through a variety of geological domains with different litho-stratigraphic and structural characteristics. The north-western part of Apulia includes the Daunia Mountains, which are made of the frontal thrust sheets of the southern Apennine chain and are characterized by a diffuse presence of clay-rich flysch sequences. To the east of the Daunia Mountains there is the Tavoliere area, which represents a part of the Apenninic foredeep; this area includes few hundred meter thick alluvial plain deposits overlying a carbonate platform. Still further east, there is the Apulian carbonate platform, locally constituting the Apennine chain foreland. This area includes two major blocks separated by transverse fault systems: i) the Gargano plateau, to the north, more uplifted and affected by active fault systems, and ii) the Murgian plateau, topographically lower and less seismically active. Recent deposits of incoherent materials of different types locally cover both blocks. Ambient noise measurements. Measurements of ambient noise were carried out in different municipalities at sites assumed to have different seismic responses and within the zones most relevant for the SM, e.g. in built up areas or near strategic infrastructures for the emergency management. At this stage, the measurements were acquired for 6 municipalities located on the Daunia Mountains, 6 in the Tavoliere plain and 3 in the Gargano area. Overall, 589 noise recordings at 345 sites have been acquired to date. The ambient noise data have been acquired with different instruments and processed using different software. The guidelines given to professionals recommend the acquisition of