Distribution of Rayleigh Wave Microseisms Constrained by Multiple Seismic Arrays

Microseisms are the most energetic signals of Earth's ambient noise field. Locating the sources of microseisms helps us to understand arrivals on noise cross‐correlation functions (NCFs) and the asymmetric amplitude of Rayleigh waves on the positive and negative parts of the NCFs. Using a dense broadband seismic array in eastern China, we investigated temporal and spatial characteristics of Rayleigh wave microseisms in the frequency range of 45–155 mHz by conducting beamforming and Rayleigh wave amplitude‐azimuth variation analyses. Seasonal variations of incident direction are clearly observable at the primary microseisms frequency band (45–95 mHz) but are less prominent at the secondary microseisms frequency band (95–155 mHz). The beamforming and amplitude‐azimuth variation analyses also indicated that microseisms arriving at the array are dominantly from five back azimuthal bands. To locate the source areas of the observed microseisms, we combined noise data from two additional arrays in southern California and employed a multi‐array beamforming technique to constrain plausible microseisms' source areas. We found that microseisms of the five azimuthal bands were excited at the Southern Ocean, western coast of Europe, coastal areas of the North Pacific Ocean, the Kerguelen Islands in the southern Indian Ocean, and the Polynesia islands in the South Pacific Ocean, respectively.