GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 2.2 GNGTS 2024 Site Response Analysis in the Agri valley (Basilicata) using the Generalized Inversion Technique G. Laurenzano 1 , N. Tragni 2 , P. Klin 1 , TA Stabile 2 , MR Gallipoli 2 & PRIN SERENA WP06 WG 1 Is9tuto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS (Triste, Italy) 2 Na9onal Research Council of Italy - CNR-IMAA (Tito Scalo, Italy) The inclusion of site amplificaCon effects caused by local geo-lithological features could bring a considerable improvement in the assessment of seismic hazard (e. g. Mascandola et al., 2023). A wide range of approaches is used today to analyze the site response, but the modaliCes for their opCmal applicaCon are sCll under debate. As part of the work package “Empirical tesCng and calibraCon” of the ongoing PRIN project “Mapping seismic site effects at regional and naConal scale - SERENA”, this study presents the applicaCon of the Generalized Inversion Technique - GIT (Castro et al., 1990) to evaluate the frequency- dependent local seismic amplificaCon at 24 sites in the Agri Valley (southern Basilicata). The Agri Valley is a NW-SE trending intermontane basin, which mainly developed during Quaternary draining of a large sector of the Southern Apennines. The High Agri Valley is a tectonically acCve area characterized by high seismic hazard related to fault systems capable of generaCng up to M = 7 earthquakes (i.e., the 1857 Mw = 7 Basilicata earthquake). The analyzed sites are distributed over an area of about 800 km 2 and correspond to the locaCons of seismic staCons that belong to three permanent seismic networks. The sites are characterized by a variety of lithologies, ranging from alluvial, lacustrine, swamp and marine deposits to eluvial and colluvial deposits, siliciclasCc sedimentary rocks and carbonate rocks. Site amplificaCon funcCons are esCmated by means of an implementaCon (Klin et al., 2021) of the one-step nonparametric GIT based on the convenConal decomposiCon of the S-wave phase in terms of source, propagaCon, and site response. The used database of earthquake recordings consists of more than 2000 waveforms recorded between 2016 and 2018 and includes local and regional events in a distance range of up to 400 km, ensuring good azimuthal coverage for each staCon. The evaluated site amplificaCon funcCons are compared to both earthquake and micro-tremor horizontal-to-verCcal spectral raCos. Finally, the amplificaCon funcCons are used to evaluate the FA amplificaCon factors in three period bands of engineering interest (0.1 – 0.5 s, 0.4-0.8 s, and 0.7-1.1 s). The results evidence high FA amplificaCon factors (up to values of the order of 5) in the low and medium period bands for staCons located on sedimentary deposits. A more detailed invesCgaCon on possible correlaCons between the measured amplificaCon and the site geomorphological characterisCcs is under progress.