Loud seismic noise from small and remote ocean waves

Seismic noise is increasingly used for monitoring the solid Earth (volcanoes, seismic faults) and storms at sea because we know that this noise is mostly generated by ocean waves. However, the detailed location of noise sources is still debated. A previous work established that numerical wave models could be used to estimate the magnitude and location of this noise. The study published these days in Geophysical Research Letters takes this one step further by showing that the loudest sources of noise are caused by the head-on collision of small swells in the middle of the ocean, which radiate seismic waves along the oceanic and continental crust, all the way to land stations. This interpretation is based on the analysis of noise polarization recorded all around the source, and the good fit between observed and modeled seismic data. These loud noise events should not be mistaken for extreme wave events when analyzing the noise record in terms of sea state. These events, recorded by many stations, may also provide a basis for estimating the attenuation of seismic waves and thus the properties of the Earth.