Infragravity waves in the deep ocean: Generation, propagation, and seismic hum excitation

[1] Oceanic infragravity waves are investigated as a possible source of seismic free oscillations, often referred to as the ‘‘hum’’ of the Earth, using a numerical model of depth-independent, nondispersive, long-wave dynamics with a forcing from nonlinear interactions among the primary wind waves (including swell). Because of near-resonant amplification, the structure of the primary-wave forcing field in shallow water, and an edge-trapping mechanism, infragravity waves are excited very effectively near the coasts. Deep-water infragravity waves are significantly influenced both by offshore leakage and propagation of the coastally generated free waves and by deep-water primary-wave forcing. With the inclusion of ‘‘mesoscale’’ variability on top of the more slowly varying primary waves generated in synoptic storms, the deep-water infragravity waves are found to have an amplitude on the order of a millimeter in height, which is consistent with field observations and considered to be sufficient to account for local hum excitation in the middle of the basin.