GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 The amplification factors defined in the microzonation studies: [2] 1− 2 = 1 2 ∫ 1 2 ∫ = 〈 〉 〈 〉 in which Sa and Sb are the acceleration response spectrum at surface and outcropping bedrock, respectively and the values of T1 and T2 are defined for three intervals: i) 0.1-0.5s; ii) 0.4-0.8s; iii) 0.7-1.1s. Following Priolo et al. (2020), we simply estimate the amplification factors by a ratio between the average values of Sa and Sb (indicated as <Sa> and <Sb> in eq. [2], respectively) in the reference interval. Then, considering that we can compute Sa=Sb*exp( δ S2S800), the amplification factors can be computed as: [3] 1− 2 = 〈 〉•〈 ⁡(δ 2 800 )〉 〈 〉 = 〈 ⁡(δ 2 800 )〉 Results For some stations available in the ITACA database (ITalian ACcelerometric Archive v.3 .2; Russo et al. 2022) and belonging to the RAN (Rete Accelerometrica Nazionale) seismic network, managed by the Italian Department of Civil Protection (network code IT), two plots are shown: the first (on the left) shows the values of the empirical amplification calculated as exp( δ S2S800) as a function of period, along with the confidence band (dashed) bounded by the first and third quartiles of the distribution of the observations ( 2 + ), in gray; the second plot (on the right) is the result of Eq. [2] for the three intervals, computed for the median values and the two quartiles. The top panel shows the site term of the station located in the Gubbio plain (station code: GBB; https://itaca.mi.ingv.it/ItacaNet_32/#/station/IT/GBP) ; GBB is installed on a class EC8-C (CEN, 2003) with measured VS,30=224m/s, showing significant empirical amplification at the long periods. Indeed, the median empirical FA values increase reaching values greater than 4 for the longest period interval. The middle panel shows the result for the Nocera Umbra station (station code: NCR; https://itaca.mi.ingv.it/ItacaNet_32/#/station/IT/NCR) , which instead belongs to the EC8-E class (VS,30=555m/s): unlike the previous case, the station amplifies at short periods and the FA value > 2 in the period range 0.1-0.5s. Finally, the Leonessa station (station code: LSS; (Leonessa; https://itaca.mi.ingv.it/ItacaNet_32/#/station/IT/LSS) has a VS,30 = 1100 m/s (EC8-A) and shows a flat and de-amplified trend throughout the period range of the spectrum. AF values that are -on average- smaller than 1 and are consistent with the classification of the reference rock sites, according to Lanzano et al. (2022b).