Site Response Implicatins of Using vs Profiles Derived From “Blind” and Geologically-Guided Surface Wave Inversions

Abstract eng:
Linear-elastic (LE) and equivalent-linear (EQL) site response analyses were performed on two unique sets of Vs profiles, both of which were derived from the same surface wave data measured at Hagley Park in Christchurch, New Zealand. The first set of Vs profiles, Analysis 1, was developed using normally dispersive inversion parameters and did not account for the complex local geology. The second set of Vs profiles, Analysis 2, incorporated strong velocity reversals in the inversion parameters where marine sands, silts, and clays were known to reside below stiffer alluvial gravels. The influence of the presence or lack of velocity reversals on the predicted site response is considered. Fifty Vs profiles from each analysis whose theoretical dispersion curves matched the experimental dispersion data approximately equally-well were sampled and used in LE and EQL site response calculations. Overall, LE and EQL site response predictions for Analyses 1 and 2 were quite similar. This suggests that despite major differences in the input Vs profiles, those Vs profiles with similar dispersion misfit values exhibit similar site response. Additionally, median and “bounding-type” statistical Vs profiles (i.e., the median Vs profile +/- 20%) were considered. The theoretical dispersion curve derived from the median Vs profile fit the experimental dispersion data well and the LE and EQL site response were in satisfactory agreement with results from the inversion Vs profiles. However, theoretical dispersion curves derived from the +/-20% Vs profile did not fit the experimental dispersion data well and the site response results were outliers relative to the other Vs profiles, with the differences becoming more pronounced with ground motion intensity.

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