Two-dimensional dynamic finite element simulation of sedimentary basin effects: a case study of Dayao

The two-dimensional (2D) linear and nonlinear seismic response of the Dayao sedimentary basin in Yunnan was investigated using the dynamic finite element method (FEM). This study systematically evaluates the effects of basin edge topographic slope, soil stratigraphy, and soil properties on surface ground motion characteristics. The key seismic response indicators were analyzed, including the displacement amplification coefficient at soil layer observation points, the spectral ratio ( H _S / H _R ) of horizontal and vertical acceleration responses between the sedimentary soil layer and reference bedrock sites (site/reference), and comparative assessments of linear and nonlinear acceleration responses. The results indicate that the horizontal displacement amplification coefficient consistently exceeds its vertical counterpart under SV wave incidence, with maximum values of 4.2 and 2.5, respectively. Moreover, the amplification coefficient gradually decreases from the basin edge toward the sedimentary center, demonstrating a spatial attenuation effect. In contrast, under P wave incidence, the vertical displacement amplification coefficient exhibits a trend opposite to that of the horizontal component. Notably, at incidence angles of 30° and 60°, the vertical amplification coefficient reaches a peak of 3.5, whereas, at 85°, it drops to a minimum value of 0.2, highlighting the dependence of amplification on seismic wave incidence angles. Regarding spectral characteristics, the predominant periods of spectral ratio under SV wave incidence are 0.1 ~ 0.4 s in the horizontal direction and 0.2 ~ 0.5 s in the vertical direction. Conversely, under P wave incidence, the predominant periods of spectral ratio are 0.2 ~ 0.5 s in the horizontal direction and approximately 0.1 s in the vertical direction. The spectral ratio curves exhibit predominantly multi-peak characteristics, indicating complex wave interference and resonance effects within the basin. Furthermore, under strong seismic motion conditions, the nonlinear acceleration response spectrum within the period range of 0.01 ~ 0.4 s is consistently lower than its linear counterpart. This finding underscores the critical role of sedimentary soil nonlinearity in altering surface seismic responses and significantly influencing the predominant periods of seismic ground motion.