Large-scale two-dimensional nonlinear FE analysis on PGA amplification effect with depth and focusing effect of Fuzhou Basin

Abstract

Based on the explicit finite element (FE) method and platform of ABAQUS, considering both the inhomogeneity of soils and concave-convex fluctuation of topography, a large-scale refined two-dimensional (2D) FE nonlinear analytical model for Fuzhou Basin was established. The peak ground motion acceleration (PGA) and focusing effect with depth were analyzed. Meanwhile, the results by wave propagation of one-dimensional (1D) layered medium equivalent linearization method were added for contrast. The results show that: 1) PGA at different depths are obviously amplified compared to the input ground motion, amplification effect of both funnel-shaped depression and upheaval areas (based on the shape of bedrock surface) present especially remarkable. The 2D results indicate that the PGA displays a non-monotonic decreasing with depth and a greater focusing effect of some particular layers, while the 1D results turn out that the PGA decreases with depth, except that PGA at few particular depth increases abruptly; 2) To the funnel-shaped depression areas, PGA amplification effect above 8 m depth shows relatively larger, to the upheaval areas, PGA amplification effect from 15 m to 25 m depth seems more significant. However, the regularities of the PGA amplification effect could hardly be found in the rest areas; 3) It appears a higher regression rate of PGA amplification coefficient with depth when under a smaller input motion; 4) The frequency spectral characteristic of input motion has noticeable effects on PGA amplification tendency.