GNGTS 2022 - Atti del 40° Convegno Nazionale

320 GNGTS 2022 Sessione 2.2 among stations recording the Amatrice earthquake within an epicentral distance of 150 km and potentially prone to experience site amplification effects because of lying in particular site conditions (sedimentary basins, topographic irregularities, fault zones). The evaluation of amplification curves best suited to describe local effects is of great importance because many towns and villages in central Italy are built in very different geomorphological conditions, from valleys and sedimentary basins to topographies. In order towell reproduce observed groundmotions, we accounted for the site amplification effect by testing various generic and empirical amplification curves such as Horizontal-to- Vertical Spectral Ratios (calculated from Fourier spectra using both earthquakes, HVSR, and ambient noise, HVNSR, recordings), and those derived from the Generalized Inversion Technique (GIT). The site amplifications emanated from GIT improve the match between observed and simulated data, especially in the case of stations installed in sedimentary basins, where the empirical amplification curve effectively reproduces spectral peaks (ex. Gubbio and Sulmona sedimentary basins, see Figures 1 and 2). On the contrary, the worst performances are for the spectral ratios between components, even compared to the generic site amplification, although the latter ignores the strong bedrock/soil seismic impedance contrasts. At sites on topography, we did not observe any systematic behavior, the use of empirical curves ameliorating the fit only in a small percentage of cases. This is a novel application considering that usually studies adopting stochastic modelling refer to bedrock conditions, or otherwise they use generic site amplification curves. Conversely, empiric site amplification curves that we implemented in our simulation, are able to account for site-specific frequency effects caused by local geological structure. Therefore, our results may provide a valuable framework for developing ground-motion models for earthquake seismic hazard assessment and risk mitigation, especially in urban areas located in the seismically active central Italy region. Fig. 2 - Velocity time series at Gubbio (panel A) and Sulmona (panel B) sites. In black, we plot recorded seismo- grams (arithmetic mean of the two horizontal components). Colored lines depict synthetic hybrid seismograms obtained from the HF and LF contributions (see section 2.3), obtained through the EXSIM code seismic source inversion by Tinti et al. (2016). They were obtained by using empirical site curves in the EXSIM code: GIT (green), HVSR (cyan), and HVNSR (blue).