Study On The Characteristics And Generation Mechanism Of Microseisms Generated By Typhoons

Microseisms(0.05-0.50Hz) are mainly generated by the coupling between ocean waves and the solid Earth. Typhoons generate large ocean waves on the sea surface and the energy can be transferred into seismic waves and recorded as microseisms. As the complexity of the energy transmission and coupling process among Atmosphere-OceanSolid Earth, the generation mechanisms and source locations of microseisms are still under debate. We analyze the microseisms generated by typhoons with continuous seismic record in Japan, Southeastern China and Taiwan as well as numerical modeling. We identify two types of generation regions for DF microseisms:(1) Coastal excitation region, where ocean waves generated by typhoons propagate towards coastlines and interfere with following incident ocean waves after reflection to form standing waves, and induce pressure fluctuations on the seafloor and generate DF microseisms;(2) Excitation region near typhoon center, where standing waves can be formed in the left-rear quadrant of the typhoon center during its moving by the interaction of two wave trains with same frequency but opposite propagation directions. And the microseisms are dominantly generated by coastal source regions in our cases. In addition, we also investigate the potential influence factors by utilizing re-analysis ocean wave data, ocean wave buoy record, and analyzing the characteristics of ocean waves under the condition of typhoons. We find that the microseisms generated by coastal source regions correlate well with the intensity of ocean wave at the coastal source regions, the distance from stations to the coastal source regions and the distance from typhoon center to coastlines, while the microseisms generated by the source region near typhoon center is mainly controlled by the characteristics of the ocean wave field around typhoon center. In order to investigate further the source regions of microseisms, we locate the source regions using polarization method, and the estimated source regions are mainly located around the coastal areas with relatively strong ocean waves, which is consistent with the results of numerical modeling. This work helps us understand the characteristics of the microseisms from typhoons and corresponding generation mechanisms, and solid the fundament for the development of seismic/acoustic monitoring of typhoons based on microseisms.