Characteristics of double-frequency microseisms in the central and northern Atlantic Ocean

The splittings of double-frequency microseisms have been observed from the published spectra of microseisms at the seismic stations on both sides of the Atlantic Ocean. However, the splitting mechanism has not been investigated yet. In this paper, the seismic data of the year 2015 recorded by five seismic stations located on both sides of the central and northern Atlantic Ocean are processed. We calculate power spectral density of the ambient noise and obtain corresponding probability density function. And we also perform polarization analysis to study the distribution of azimuth of main source regions at the periods of double-frequency microseisms.The results show that significant splittings of the double-frequency microseisms are observed at the five stations located on both sides of the central and northern Atlantic Ocean, the peak periods observed at each station were different and the source regions from the same direction and different directions are both capable of generating the splitting of double-frequency microseisms. The power spectral density （PSD） of microseisms in the central and northern Atlantic Ocean varies with seasons. Some stations have stronger PSD amplitudes in winter than in summer, and the others have stronger amplitudes in summer than in winter. The main source region directions of the central and northern Atlantic stations are not affected by seasons. Therefore the main source region directions remains almost the same in winter and summer, and the source region directions of the two seasons overlap in a wide range. For the stations located on the east coast of the central and north Atlantic Ocean, the main sources of the double frequency microseisms are more from the Atlantic Ocean to the south of the stations in summer, and more from the Atlantic Ocean to the north of the stations in winter. For the stations nearby the Caribbean Sea on the west coast of the Atlantic Ocean, the source directions of the double-frequency microseisms mostly point to the Caribbean Sea in both winter and summer. For the station MPG located at the lowest latitude in this study, the double-frequency microseisms mainly come from the Atlantic Ocean to the north of the stations in winter, while it has additional sources from the southwest directions in summer, probably from the Pacific Ocean.