Questioning the applicability of soil amplification factors as defined by NEHRP (USA) in the Israel building standards

In this study we examined the applicability of the NEHRP soil classification which is based on the VS,30 parameter and the corresponding Fa and Fv factors to correct acceleration response spectra for local site classification. We calculated acceleration response spectra (10% in 50 years) for more than 1900 sites across Israel. Computations were made for hard rock conditions and for the actual site conditions, while considering nonlinear response of the soils. Based on synthetic acceleration response spectra of real sites (using stochastic procedures), it is concluded that generalizing site classification and consequently, amplification, by means of a single parameter VS, 30 is not recommended. The geology of Israel is complex and may vary significantly over short distances. Sites of similar class, show different soil effects both in shape, amplitude and in frequency. In many cases there is no correlation between amplification and VS, and in other cases, the scatter is unacceptably high.