Site amplification factor model for Sichuan region considering nonlinear soil effects

To investigate the effect of site amplification on ground motion in Sichuan region, strong motion data and calculated equivalent-linear results are analyzed using 897 strong motion records and 105 shear-wave velocity profiles from the region. Based on the analysis results, the influence of the ground motion intensity and site conditions on site amplification is studied, and site amplification factor model considering nonlinear soil effects is established. Then the application effect of the model to evaluate ground motion is discussed. The results show that the decreasing extent of site amplification factor with the increasing Vs₃₀ is period-dependent at low shaking levels. The decrease is mostly significant at period of 0.2 s. Under high shaking levels the decreasing extent of site amplification factor with the increasing ground motion intensity is spectral period-dependent but the site amplification factor is independent of the ground motion intensity at a periods larger than 1 s. In addition, the soil nonlinearity has less influence on ground motion with the increasing Vs₃₀. When value of Vs₃₀ is larger than 500 m/s, the influence can be neglected. In conclusion, compared with attenuation relationship considering only linear soil effects, the standard deviation of ground motion estimates in Sichuan region using the proposed model can be reduced significantly. Especially for the near field and the short period ground motion, the reduction can reach 12%.