Investigation of topographic amplification on ground motions considering spatial variability of soil properties

The amplification of seismic waves due to surface topography and subsurface soils is a significant factor contributing to seismic site amplification and consequent damage. However, conventional deterministic analysis methods can hardly account for the impact of inherent spatial variability of subsurface soil properties. This study employs a random finite element method (RFEM) to address this limitation and investigate the amplification of ground acceleration in time and frequency domains for 2D slope models with varying magnitudes of soil elastic modulus (E) and coefficients of variation (COVs). Comprehensive insights are provided through the analysis of amplification indicators related to peak ground acceleration, Fourier spectrum ratio, and response spectra of input motion. It is found that the spatial variability of E reduces the maximum amplification factor (AF) at the slope crest. Frequency domain analyses show that considering spatially variable E leads to decreasing trends in Fourier spectra and mean values of the transfer function, especially in the mid-to-high-frequency range. However, transfer functions for topographic effects exhibit high-frequency amplification in models with a higher impedance ratio. For the response spectra, the topographic amplification factor (TAF) and spectra amplification factor (SAF) at longer periods gradually increase in random simulations, indicating the potential risk for long-period structures. The findings emphasize the significance of spatial variability in soil properties for seismic amplification, providing probabilistic insights for seismic design and optimization in complex site conditions.