Localization And Analyzation Of Typhoon-induced Microseism Sources

The microseisms(~0.05-0.5 Hz,generally bordered by ~0.12 Hz and divided into single-frequency and double-frequency)recorded at seismic stations on land mainly originated from ocean wave activities.During the typhoon,the intense air-sea interactions intensify the wave activities,which further enhance the microseisms significantly.The characteristics of the microseisms would evolve with the typhoon process during the typhoon's lifecycle,making it possible to use the microseisms to study the typhoon.Therefore,this paper uses the microseisms recorded by the onshore seismic array and the island-based seismic stations,to locate and analyze the two kinds of sources of typhooninduced double-frequency microseisms.Considering the long-distance propagation ability of P-wave double-frequency microseisms,this paper uses the continuous microseism data of NorthEast China Extended SeiSmic Array and High Sensitivity Seismograph Network in Japan,to locate and track the P-wave double-frequency microseisms sources induced by Typhoon Lupit(2009),with the seismic array Beam-forming method based on 3-D earth model.Compared with the conventional 1-D-model-based beam outputs,the localization deviations and the localization correlation coefficients of the 3-D-model-based beam outputs are smaller and higher respectively,and 3-D-model-based localization results show better consistency with the typhoon trajectory and the simulated sources of double-frequency microseism.The research results show that it is feasible and effective to locate P-wave double-frequency microseisms sources induced by typhoon using the seismic array Beam-forming method remotely;3-D model is suitable for the travel-time prediction of seismic waves at medium distance and below or in complex geological structures,and can relatively improve the localization accuracy of the seismic array Beam-forming method.Typhoon-induced coastal double-frequency microseism sources are mainly generated by typhoon-induced swells propagating to the coast,reflecting and then interacting with the subsequent swells on the ocean floor.Therefore,these coastal double-frequency microseisms have dispersion characteristics corresponding to the swell dispersion.This paper selects the microseisms recorded at the seismic stations in Taiwan and the Ryukyu Islands during Typhoon Megi(2010),and obtains the frequency gradients of the coastal double-frequency microseisms by sliding-window Fractional Fourier Transform,to invert the sources of typhoon-induced swells.The results show that,sources of typhoon-induced swells inverted with the frequency-dispersed double-frequency microseisms recorded by seismic stations along the eastern coast of Taiwan have good dynamic consistency with the ocean wave data of ERA5 reanalysis provided by European Centre for Medium-Range Weather Forecasts,indicating that the inversion sources of typhoon-induced swells is relatively reliable and accurate.The researches in this paper show that it is feasible and effective to study the typhoon by using the typhoon-induced microseism source as a springboard.In addition,given that the close connection between typhoons and microseisms,researching,observing and tracking typhoons using microseisms have shown good potential for development and are expected to complement traditional observation methods.