Adjustment of site factors for basin effects from site response analysis and deep downhole array measurements in Taipei

Abstract

Abstract Local site effects can amplify seismic shaking and damage caused by earthquakes. Site factors (SF) are used in seismic design to account for these effects to modify ground motions from a reference rock site. Average shear wave velocity in the top 30\xa0m of soil (Vs,30) is typically used to predict SF. However, recent studies have shown that using Vs,30 alone may be insufficient in quantifying SF under the presence of deep soil deposits and proposed SFs that account for the bedrock depth (e.g. Z1.0, depth with Vs of 1\xa0km/s). This study evaluates these depth-dependent SFs using 1D nonlinear and equivalent-linear site response analyses. The predicted SFs are also compared with observations of downhole arrays installed within Taipei Basin. Based on numerical and observational results, depth correction factors are recommended in conjunction with SFs of seismic design code to reflect the effect of different sediment thicknesses in the design process.