Estimating near-surface shear wave velocity using the P-wave seismograms method in Japan

Using initial P-wave records at 298 seismic stations from the Kiban-Kyoshin network (KiK-net), the P-wave seismograms method is employed to estimate the near-surface shear wave velocity in Japan. The applicability of this method is validated by comparisons between the measured and estimated time-averaged shear wave velocity to depth Z(VSZ, 5<Z<300 m). Using a second-order polynomial regression relating log VSZ and log VS30, the estimated VS30 values agree well with the measured values. We also find that VS30 is directly related with the ratio of radial to vertical components of the initial P-wave velocity time series (RP). Compared with the theoretical method, the empirical relationship between RP and VS30 has an improvement in the accuracy for VS30 estimation, is basically region-independent for Japan and Central and Eastern North America (CENA), does not need any other parameters, and is potentially useful for other regions of the world.