PSI - Issue 78

Fadel Ramadan et al. / Procedia Structural Integrity 78 (2026) 859–866

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Figure 2.1 – Datasets used in this study: ITA18 and NESS1.0 dataset.

2. Calibration of a scenario-dependent corrective factor of VH-ITA18 to incorporate the influence of near source effects on the VH ground motion ratio based on the global recordings of NESS1.0 (the final model is named VH ITA18–NESS). The near-source adjustment term is introduced a-posteriori following the Referenced Empirical Approach proposed by Atkinson (2008, 2010). Note that this corrective is also available for the horizontal component in the work of Sgobba et al. (2021), similarly to that developed for the VH. The final predictions of VH ITA18–NESS can be expressed as: 10 18− = 10 ( 18 ) + ( ,0) (1) where δ R represents the scenario-dependent corrective term for the reference model, and the use of the max function ensures that only positive adjustments (i.e., increment of predicted values with respect to VH-ITA18) are retained to enhance safety. Note that the standard deviation associated with VH ITA18–NESS is the same as in the reference model (VH-ITA18). Figure 3.1 illustrates the median VH spectral ratios predicted by the reference (VH ITA18) and adjusted (VH ITA18– NESS) GMMs under various earthquake scenarios, where the explanatory variables considered are: a) Joyner–Boore distance (Rjb); b) Mw; c) Style of Faulting (SoF) and d) Vs30. As expected, at short periods (T < 0.1 s), VH ratios exhibit a strong distance dependence (Figure 3.1), with values reaching up to ~1.5 at near-source distances (< 15 km). The effect of the adjustment is instead minor for events with Mw = 5.0 or lower magnitudes. Regarding the focal mechanism, the adjustment has a noticeable impact for strike-slip (SS) and thrust faulting (TF) events, whereas normal faulting (NF) shows no clear dependence on the adjustment. With respect to site conditions, the adjusted model shows a clear dependence on Vs30, particularly at short periods (e.g., 0.1 s), where the amplification effects are evident. At

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