Excitation of microseisms
Published in
Geophysical Research Letters
Publication date
13 March 2007
Abstract
A conventional view on the generation of microseisms is through the nonlinear mechanism, pointed out by Longuet-Higgins [1950], which generates pressure variation at ocean bottom. Treating the source only at the ocean bottom by this pressure effect is an approximation, however, since Rayleigh waves, the dominant wave type in microseisms, have displacement throughout the ocean and their amplitudes vary with depth. Comparison with a more rigorous normal-mode formula showed that this conventional approach fails in deep oceans. Therefore, under certain conditions, the approach by the use of the Longuet-Higgins’ pressure formula at ocean bottom may be misleading. If the source regions are in shallow water, it is justified. New evidence of nonlinearity in ocean waves from buoy data is presented to support the view that the source regions for microseism excitation is in shallow water. Therefore, the conventional use of the Longuet-Higgins pressure for the excitation of microseisms seems to be justified after all, although one should pay attention to ocean depths in the source region very carefully.