Nonlinear horizontal site amplification for constraining the NGA-West2 GMPEs

The nonlinear soil amplification models developed by Walling et al. (2008) are revisited for three main reasons: (a) the simulation database on which the models were developed has been updated and extended, (b) two alternatives for the input shaking parameter - (PGA and Sa(T)) - are explored, and (c) a constraint on the nonlinearity at long periods is removed. The model is based on site amplification factors, relative to a V_S30= 1;180 m/s site. Simulations included a wide range of soil profiles, shaking amplitudes and soil properties, from which only a subset was used herein. Finally, four models for the nonlinear site amplification are developed using two nonlinear material property models (peninsular range and EPRI) and two input-shaking parameters (PGA₁₁₈₀and Sa₁₁₈₀(T)). These results are intended for use by the NGA-West2 developers to constrain the nonlinear scaling of the site response for the horizontal ground motion models.