GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 If the reference ground motion is consistent with the engineering bedrock definition, it can be used to validate amplification coefficients proposed by standards or theoretical and/or numerical methods. In fact, recently δ S2S terms, calculated with respect to the standard definition of the bedrock (VS,30 or Vs,H=800m/s), were used to validate the amplification coefficients suggested in the new Eurocode proposal (Paolucci et al 2021). For this reason, we here introduce and compute empirically AFs that are evaluated from δ S2S estimates, which can be used to compare and validate the results obtained from microzonation studies at local and national scales (such as Falcone et al. 2021). Data and methods The analysis is based on the residual computation, i.e., the difference between the natural logarithm of the observed ground motion parameter log(Y)obs and the corresponding prediction log(Y)pred, from a reference Ground Motion Model (GMM). The residuals Res are decomposed into repeatable terms referring to event and site, as: = | + 2 | + [1] According to the Al Atik et al. (2020) notation, δ Be is the between-event residual, δ S2Ss is the site-to-site residual, and δ Wes is the event- and site-corrected residual, obtained by removing the event and station errors from Res. In this study, we focus on δ S2Ss term that quantifies the systematic deviations between observed ground-motion and predictions at a given site. The dataset used for this analysis is the ITACAext (Brunelli et al. 2022), composed of the data and metadata included in ITACA (ITalian ACcelerometric Archive) database up to 2020 December 31st, integrated with some velocimetric waveforms. The residuals are evaluated with respect to the ITA18 ground-motion model (Lanzano et al., 2019) for acceleration response spectral ordinates (SA, 5% damping). The adopted GMM is valid for the median of the horizontal component in the moment-magnitude range Mw [3.5-7.5] and rupture distance interval R [0-200km]. The computation of the residual components is performed by applying the random-effect model (Bates et al., 2015), while the associated variability is evaluated by the standard deviation of the aleatory (event- and site-corrected) residuals at the site. The δ S2Ss estimated from this dataset are disseminated through the ITACAs2s flat-file (Lanzano et al. 2022), i.e. a set of parametric tables containing the estimates of the repeatable site terms and the associated variabilities. ITACAs2s is available on the ITACA 3.2 website (Russo et al. 2022; https://itaca.mi.ingv.it/ItacaNet_32/#/products/itacas2s_flatfile ) and includes the site-to-site term of 1,922 stations in Italy and in the surrounding countries (France, Switzerland, Slovenia, and Greece). These terms can be exploited to have an overview of the amplifications and peculiar features of the Italian recording stations. For the purposes of our analysis, the site-to-site residuals are computed with respect to generic rock conditions of ITA18-SA, i.e., VS,30=800m/s, hereinafter δ S2S800. In this way, the amplification functions are consistent with those proposed for the technical norms, for which the reference level is set at VS,30=800m/s.