Shear-wave velocity structure from the near-surface to mid-crust beneath the southern Korean Peninsula using P-wave polarization analysis

Abstract The near-surface velocity structure provides critical information for seismic hazard assessment, ground motion simulation, and site amplification studies. However, accurate estimation typically requires costly core sampling from boreholes and/or seismic exploration. As an alternative, we estimated near-surface to mid-crustal shear-wave velocities in the southern Korean Peninsula using P -wave polarization analysis, which utilizes only the incident angles of direct P waves from earthquakes. We extended the polarization analysis by employing several different frequency bands to estimate shear-wave velocities from the surface down to the mid-crust. P waveforms were bandpass-filtered with three different frequency bands (0.05–0.3 Hz, 0.5–2 Hz, and 3–10 Hz) to determine shear-wave velocities at different depths. The P -wave polarization results show a strong correlation between geological features and velocity distributions across the frequency bands. The P -wave polarization results for the frequency bands of 0.05–0.3 Hz, 0.5–2 Hz, and 3–10 Hz indicate velocity distributions of 3.50 ± 0.35 km/s, 3.00 ± 0.69 km/s, and 2.26 ± 0.69 km/s, respectively. Comparison with velocity structures estimated from Rayleigh-wave ellipticity and site surveys reveals that these values from frequency bands of 0.05–0.3 Hz, 0.5–2 Hz, and 3–10 Hz correspond to average velocities from the surface to depths of 3–16 km, 0.1–3 km, and 5–100 m, respectively. The polarization analysis demonstrates superior performance in estimating near-surface shear-wave velocity compared to the Rayleigh-wave ellipticity method.