Site amplification model for Croatia estimated by random vibration theory-based site response analysis

This study presents a first developed site amplification model for Croatia using random vibration theory (RVT)based site response analysis and measured shear wave velocity (Vs) profiles for different site parameters (VS30 - average shear wave velocity in the top 30 m, fundamental site frequency/period; H800 - depth to the bedrock layer with reference to shear wave velocity VS = 800 m/s). The impedance between the topsoil layers and the engineering bedrock in the measured Vs profiles is more prominent than that in the soft transition modelled in the theoretical soil profiles. The results indicate that (i) the site amplification factors (AFs) are greater than that of the code-based AFs (current and revised Eurocode 8) for stiff soil/soft rock sites and (ii) significant nonlinearity in soft soils occur compared to that of recent ground motion models because of difference in variability between the measured and theoretical Vs profiles. These observations imply significant deviations from the site factors computed based on the site response models in this study and recent models, as well as from those provided in the present Eurocode 8 and its revised version. The presented site AF model based on different site parameters (VS30, frequency/period or bedrock depth) can be integrated into existing or future developed regional ground motion models to characterize the influence of site effects on design response spectra following the variability in soil profile properties on weak and strong seismic responses. This is especially important when used in seismic hazard studies in areas with sparse empirical ground motion database.