Fig. 4
From: Seismic noise between 0.003 Hz and 1.0 Hz and its classification
The relative size of the excitation of Rayleigh waves between the normal mode theory and the Longuet-Higgins formula. The five lines are for different ocean depths from 1 to 5 km. At low frequencies, the ratio approaches 1 and shows quantitative agreement. At frequencies of the secondary microseism, they differ but that is because the formula (Eqs. 2 or 4 in the text) does not contain the depth resonance effects. Longuet-Higgins (1950) discussed this depth effect which was correctly used by Kedar et al. (2008) and Ardhuin et al. (2011)