Characteristics of seismic noises excited from three typhoons in the western Pacific

Typhoons play an important role in the atmospheric circulation. Strong winds from typhoons excite ocean waves that accompany seismic noises. The primary and double frequency microseisms are dominant in frequencies of 0.05-0.1 Hz and 0.1-0.4 Hz. We investigate the characteristics of seismic noises from three typhoons that include Son-tinh in October 2012, Bopha in November 2012, and Soulik in July 2013. The peak wind speeds were 148-184 km/h, and the central atmospheric pressures reached 925-955 hPa. The typhoons passed through the western Pacific to South China Sea. We analyzed the temporal changes in spectral amplitudes of seismic noises during typhoon periods. The amplitude of seismic noises increases with decreasing distance between typhoon and seismic station. We observe large spectral amplitudes in frequencies of 0.1-0.4 Hz, which corresponds to the dominant frequencies of the double frequency microseism. The seismic energy in the frequency band of the primary frequency microseism was relatively weak. The seismic-noise amplitudes displays high correlation with the equivalent pressures on ocean bottom from Wave Watch III model. The observation suggests that the seismic noises may be originated from the ocean waves. The dominant frequency of seismic noises generally increases after passage across the stations due to the dispersion of ocean waves. Also, the dominant frequencies of seismic noises from the typhoons in the South China Sea appear to be higher than those from the typhoons in the Pacific. This feature may allow us to identify the origin of seismic noises and the nature of typhoons.