Shear Wave Velocity Estimation in Korea Using P-Wave Seismograms

Abstract

The average shear wave velocity for a soil depth of 30 m (V_S30) is crucial for seismic hazard assessments. However, V_S30 measurements are not available at most recording stations in Korea. The P-wave seismogram method is an efficient way to estimate V_S30 because it only utilizes P-wave seismograms recorded on the ground surface without boring process. V_S30 measurements for 51 recording stations are acquired from previous literature, and downhole tests were performed at 10 stations for additional V_S30 measurements. The P-wave seismogram method is validated for 50 stations using 359 seismograms recorded during 66 earthquake events with local magnitudes greater than 3.0. The average shear wave velocity for a certain depth (V_SZ) can be estimated using the ratio of radial to vertical components in the initial P-wave velocity seismograms, which can be converted to V_S30 using an empirical relationship. The residuals between the measured and estimated V_S30 are divided into the overall bias, between-site residuals, and within-site residuals. The standard deviation for between-site residuals is 0.37, which is comparable with the values of previous studies for other countries. After bias correction, 70% of measured V_S30 and estimated V_S30 are within ±50% of each other. This study estimates V_S30 values for 118 stations where V_S30 is not available.