Open AccessExcitation of normal modes by non‐linear interaction of ocean waves
Author(s) -
Tanimoto Toshiro
Publication year - 2007
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2006.03240.x
Subject(s) - microseism , forcing (mathematics) , seismic noise , excitation , noise (video) , range (aeronautics) , normal mode , term (time) , geophysics , physics , geology , mode (computer interface) , seismology , computational physics , acoustics , atmospheric sciences , computer science , materials science , vibration , quantum mechanics , composite material , artificial intelligence , image (mathematics) , operating system
SUMMARY Recent development in seismology has shown that seismic noise is a useful source of Earth structure study. Non‐linear interaction of ocean waves is considered to be one of the important causes for seismic noise, although source locations and detailed mechanisms are not clear yet. In order to improve our understanding of this mechanism quantitatively, we derive a normal‐mode excitation formula due to this effect. Longuet‐Higgins' pressure formula naturally comes out from the vertical forcing term in the excitation coefficient. A novel aspect of our formula is the horizontal forcing term that becomes comparable to the vertical forcing term for frequencies below about 5 mHz (millihertz), especially in shallow oceans. This term is not likely to be important for microseisms because the main frequency range of microseisms is about 0.05–0.4 Hz but it may make significant contributions to the excitation of the continuous background oscillations (the hum) whose frequency range is 2–7 mHz.