Evaluation of Site Amplification Factors on the Seafloor for Use in Earthquake Early Warning for Railways Based on Accumulated Seismic Data

Since November 2017, the earthquake early warning for Shinkansen uses ocean bottom seismometer, and an alarm is issued when the ocean bottom seismometer exceeds the threshold.The threshold is set by multiplying the reference value that changes with distance from Shinkansen line to seismometer due to attenuation and the site amplification factor of seismic motion due to soft sedimentary layer beneath the seafloor.However, the site amplification factor is poor accuracy, because that factor is set to the average value at all observation points since there was little observation data when the ocean bottom seismometer was introduced.Therefore, in this study, we proposed a method to set precise site amplification factor according to the installation environment of the ocean bottom seismometer by utilizing the accumulated seismic data observed by the ocean bottom seismometer.