Nonlinear dynamic behavior and basin edge effect in the clayey basins under simultaneous P and SV incident waves

In the estimation of the design spectrum for sites with topographic irregularity, the instructions of the earthquake codes are to use the horizontal components of the motions. Although this approximation remains conservative for horizontally layered conditions, the effect of the P wave component at basins with 2D/3D bedrock geometry, due to the complicated interaction among different wave types, would affect the basin amplification behavior. The major contribution of this study is to present a quantitative ratio in terms of amplification factor for comparison between the simultaneous P+SV and only SV incident wave condition. To attain this goal, a fully nonlinear analysis method capable of simultaneously application of the P and SV incident motions in time domain is utilized. In this study, the effect of parameters such as clay type and basin depth is investigated. The results show the effect of the P+SV cases on the frequency content of the surface response with respect to the only SV case. It was seen that for the basin with 50m depth the aggravating effect of the P+SV incident wave remains under 20% for both soft and stiff clay types. This ratio reaches to 25% for 100 m depth basins. Along with the aggravating effect, the results show a 10% to 20% suppressive effect of the P+SV especially at basins' center with dominant 1D behavior.