Near-surface to upper crustal shear-wave velocity structure beneath Gangwon Province, South Korea, using P-wave polarization analysis

Estimating the crustal velocity structure is crucial for understanding the tectonic evolution of continents. In particular, the structure of the near-surface crust provides critical insights into site effects, ground motion, and disaster prevention. In this study, we applied P-wave polarization analysis to estimate the shear-wave velocity structure beneath 75 seismic stations installed in Gangwon Province, South Korea, a region characterized by complex geological features. A total of 302 teleseismic events were utilized for this analysis. The P-wave polarization method relies solely on the incident angles of direct P waves recorded at individual stations, ensuring that the results are independent of the network's spatial density. P waveforms were bandpass-filtered using six different central frequencies ranging from 0.1 to 3.2 Hz, enabling the derivation of velocity structures across a broad range of depths. Additionally, we calculated depth sensitivity kernels for P-wave polarization at the six central frequencies using a numerical approach. P-wave polarization at frequencies of 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 Hz exhibited the highest sensitivity to shear-wave velocities at depths of 7.3, 4.3, 2.1, 1.1, 0.5, and 0.3 km, respectively. Based on these sensitivity kernels, the results demonstrate significantly improved accuracy compared to previous models and effectively capture geological features such as faults and rock distributions. Notably, the resolution at depths of several hundred meters, which are challenging to estimate using conventional seismic surveys or tomography methods, was enhanced. This highlights the potential of P-wave polarization analysis as a valuable tool for seismic imaging.