Extracting Rayleigh-Wave Dispersion Curves From Microseism Noise Recorded at a Single Ocean Bottom Seismograph

Abstract

It is a widely adopted method to use the Rayleigh-wave dispersion curves to constrain the shear-wave velocity structure under the ocean. Traditional methods generally utilize ambient noise cross correlations between stations and teleseismic surface wave records to extract the dispersion curves. In this study, we develop a method that uses the microseism noise recorded at a single station to derive the Rayleigh-wave dispersion curves. The fundamental idea is that the ocean-bottom pressure and vertical acceleration of microseism noise satisfy a theoretical equation which depends on the wave frequency and phase velocity. By applying the method to the Cascadia Initiative data, Rayleigh dispersion curves between $3-10$ s are derived, and they are found to be consistent with the results from the ambient noise cross-correlation method. The cross-correlation method generally extracts dispersion curves in longer periods due to large spacing between stations, thus the new method provides complementary results in short periods. The extracted dispersion curves are used to estimate the shear-wave velocity and thickness of the sediment in the Cascadia area. For stations in shallow water, the new method is not applicable, and we use the compliance noise to constrain the sediment properties, providing a complete sediment model in the Cascadia area.