A national VS30 model for South Korea to combine nationwide dense borehole measurements with ambient seismic noise analysis

The average shear-wave velocity within the top 30 m from the surface, VS30, represents site characteristics including the soil classification and site amplification that are essential information for building codes and seismic design. A novel method to determine a VS30 model based on a composite analysis of borehole standard penetration test numbers (SPT N) and horizontal-to-vertical (H/V) spectral ambient noise ratios is introduced. A national VS30 model for South Korea is determined using the method. The shear-wave velocity structures beneath 20 nationwide broadband seismic stations are determined using the H/V analysis. The SPT N data are collected from 175,619 nationwide densely-distributed boreholes. The shear-wave velocity models from SPT N values are calibrated for the local reference velocity models from H/V analysis. A representative relationship between the SPT N values and shear-wave velocities is introduced. A national VS30 model for South Korea is determined using the calib...