When compared to quiet land stations, ocean-bottom broadband seismic stations show increased background noise in the band pass of interest for the study of regional and distant earthquakes. This is mainly due to deformation of the seafloor under the pressure forcing by long-period ocean surface gravity waves (infragravity waves; 0.002 to 0.05 Hz). The signal due to infragravity waves is considered to be an unavoidable nuisance for the seismic observations and post-processing is needed to remove it. However, the observations of infragravity waves at the ocean-bottom seismic stations also provide an opportunity to study the nature and characteristics of the coupling between the infragravity waves and the solid earth. This is important for the study of the infragravity wave generation and dissipation as well as for the study of Earth's continuous free oscillations (Earth’s ‘hum’) and structure using non-seismic sources.