Two-dimensional Ground Response Analyses at the Delaney Park Downhole Array Site

抄録

Many recent studies have attempted to predict surface ground motions recorded at downhole array sites using 1D ground response analyses (GRAs) and have highlighted the often-poor agreement between the simulated (i.e., theoretical) and recorded (i.e., empirical) ground motions. The Delaney Park Downhole Array (DPDA) is an example of a site where 1D analyses have consistently resulted in over-estimation of amplification when attempting to replicate empirical small-strain ground motions, and researchers have hypothesized that subsurface spatial variability is to blame for the mismatch. In this study, we first update a large-scale (1.6 km × 1.6 km × 80 m), site-specific, pseudo-3D shear wave velocity (Vs) model of the DPDA site using a geostatistical approach based on 108 horizontal-to-vertical spectral ratio (H/V) of noise measurements. We then perform 2D GRAs on cross-sections extracted from the updated pseudo3D Vs model with various lateral extents and with various azimuths. By using cross-sections along different lateral extents and azimuths, we show that 2D GRAs can result in either higher or lower amplifications relative to 1D GRAs, depending on how the simulated waves constructively or destructively interfere. Regardless, 2D GRAs remained ineffective at matching the recorded ground motions, potentially due to the complex 3D spatial variability around the downhole array, and which cannot be effectively captured by individual 2D cross-sections at certain azimuths. It is hoped that future 3D GRAs will be able to better capture the effects of wave scattering and other complex wave propagation patterns required to match the recorded ground motions at the DPDA site.