Divergence Between Nonlinear and Equivalent-Linear 1D Site Response Analyses for Different VS Realizations of Typical Clay Sites

Surface ground motions can be obtained via various methods of analysis such as equivalent-linear (EL) and nonlinear (NL) one-dimensional numerical simulations. Selection of analysis method would be a challenging issue due to difficulty of input data preparation. The uncertainty inherent in soil parameters and shear wave velocity has significant impact on the soil surface hazard analysis through amplification function. In the present study, realizations of two clay sites in Shiraz city, southern Iran, along with three hypothetical sites are selected to examine the divergence between EL and NL ground response analyses. Two constitutive models, namely modified hyperbolic Kondner–Zelasko (MKZ) and general quadratic/hyperbolic (GQ/H), are implemented in site response analyses of synthetic profiles generated for reference profiles. The GQ/H model requires user-defined shear strength to simulate soil behavior. Two approaches of shear strength estimation are utilized in the current study. Several issues related to site response analysis are investigated such as effect of shear strength estimation method, input ground-motion intensity, and soil condition on the divergence between EL and NL spectral accelerations. The obtained EL/NL spectral response ratios are presented as a function of either shear strain index or oscillator period for the abovementioned issues. Moreover, 20% difference thresholds of the shear strain index are computed and compared with those from previous researches.