Quantifying Multidimensional Effects in Linear Site Response Using 1D and 2D Simulations of Sedimentary Basins in Wellington, New Zealand

This study quantifies the influence of multidimensional effects on site response in the Wellington region of New Zealand by comparing results from different simulation approaches. Response‐spectral amplification functions from 1D and 2D site response analyses are compared to quantify the magnitude and spatial distribution of multidimensional effects, which are significant at some locations. The 1D and 2D results are also compared to observations at strong motion stations. Simulated surface‐to‐borehole transfer functions are extracted from 1D and 2D site response models to show their sensitivity to subsurface stratigraphy and surface topography. Comparisons with observed spectral amplification indicate that the 1D and 2D models capture key spatial trends and, on average, are within 20–30% of the simulated values over the full period range. While results from the two approaches are not significantly different at most instrumented sites, the 2D analyses suggest that the high observed amplification at moderate to long periods is likely influenced by multidimensional effects at some sites. Topographic and stratigraphic features that influence site response are identified, and these features are shown to cause significant differences between 1D and 2D transfer functions over a large spatial extent, consistent with recent global studies demonstrating that many sites do not exhibit surface‐to‐borehole transfer functions consistent with 1D assumptions. In contrast, the differences in response‐spectral amplification between 1D and 2D analyses are smaller than those for within transfer functions, suggesting that care should be taken to avoid over‐inferring the performance of 1D site response modeling techniques using only transfer functions from vertical arrays.