2D site response in alluvial basins by finite difference-based numerical method

The lateral irregularity of the soil media is typically formed by fault ruptures or topographic depressions filled with sediments and this highly present geological formation is identified as a basin. On this type of project site, the estimation of the surface ground motion of an earthquake is a complex problem in geotechnical earthquake engineering. Contrary to the soil column assumption of the semi-infinite 1D soil model, the soil layers have both horizontal and vertical discontinuities and change topographically and stratigraphically. Therefore, the question of how the soil response would be shaped as a result of combinations of the effects of principal wave phenomena in the sedimentary basins, surrounded by roughly circular or elliptical harder layers or the bedrock outcrops, is still a leak in the seismic code provisions. In this study, basin conditions considering soil classes as soft clay (E) which defined by NEHRP 2020 provisions was investigated with different levels of bedrock inclination. Fully nonlinear time-domain analyses were carried out on both 1D and 2D models of created basins by the Finite Difference-based numerical method. The results of the nonlinear time-domain analyses were compared to clarify the effects of the basin edge inclination on the resultant ground motions on the points located with equal intervals on the model surface. The acceleration response spectra of 2D and 1D models were illustrated across the basin, and it is aimed to explain the dependence on the motion frequency and the effect of the inclination angle of the basin edges to site response.