Excitation of Microseisms

Toshiro Tanimoto

Published March 2007, SCEC Contribution #1152

Excitation of microseisms is generally considered to be due to pressure change at ocean bottom, for which Longuet-Higgins derived his celebrated formula in 1950. Use of this formula is an approximation, however. Comparison with a more rigorous normal-mode formula shows that this conventional approach is acceptable for ocean depths less than 1 km but fails in deep oceans. On the other hand, there seems to be a multitude of evidence that source region for double-frequency microseim is near the coast and thus is generally in shallow water. An evidence from buoy data for nonlinearity in ocean waves is presented to support this view. If a source region is in shallow water, use of the Longuet-Higgins pressure formula at ocean bottom for the excitation of microseisms is justified, although one should pay attention to ocean depths very carefully.

Key Words
United States, focal mechanism, pressure, microseisms, data processing, frequency, California, shallow depth, Southern California, quantitative analysis, marine environment, Fourier analysis, ocean waves, seismic networks, ocean floors, microearthquakes, earthquakes

Citation
Tanimoto, T. (2007). Excitation of Microseisms. Geophysical Research Letters, 34, L05308. doi: 10.1029/2006GL029046.