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

초록

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.

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