Origin of microseism observed in South Korea

Ambient seismic noise has been widely used for imaging crustal structure as an alternative passive source, even where traditional seismic imaging is not possible due to low seismicity. Long before the sensational applications of seismic noise, the origin of the noise has already been studied to understand its nature and characteristics for several decades. In this study, we investigate the origin of microseism observed in South Korea. Annual spectrograms in the microseismic frequency range up to 0.4 Hz show coherent peaks at about 0.2 Hz in the winter, which is at the frequency band of the double-frequency microseism. However, the primary microseism is only rarely observed in South Korea when the Pacific typhoon is close to the Southern Sea of Korea. Polarization analysis and noise cross correlation indicate that the energy of the double-frequency microseism comes dominantly from the east of the Korean Peninsula. Comparison of the results from the operational wave model of the Korea Meteorological Administration and seismic data shows a strong correlation of spectral amplitude of seismic data with the significant wave heights and periods of ocean waves, implying that the primary and the double-frequency microseism observed in South Korea are generated at the Southern Sea of Korea and at nearby shorelines of the east coast of Japan, respectively.