Soil amplification is an important parameter to estimate the dynamic soil-structure interaction under earthquake loadings accurately. So, a good estimation of the soil amplification is required because the soil conditions of local sites have significant influences on the vulnerability of engineering structures. Although the soil amplification is directly related to impedance ratio between the rocks and soils, it is generally calculated trough empirical formulas based on Vs30 value, an average shear wave velocity (Vs) up to 30m depth. However, when the soil column includes rock units (Vs□700m/s) within the 30m depth, the empirical formulas lose their validity. In this study, we try to explain this issue and compare soil amplification values calculated by using Vs30 and impedance ratio for synthetic models and field cases which include rocks unit within the 30m depth. In synthetic models, the soil amplification for four scenarios for two-layered medium is calculated by most known empirical formulas and compared with that of impedance ratio. In field cases, we compare soil amplifications for shallow and deep bedrock cases. Synthetic and real results show that soil amplifications calculated by empirical formulas couldn’t characterize the real ground conditions, especially in the case of the hard-solid units in shallow depths.


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