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Observed envelopes of coupled seismic free oscillations
Author(s) -
Park Jeffrey
Publication year - 1990
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl017i010p01489
Subject(s) - physics , envelope (radar) , attenuation , oscillation (cell signaling) , coupling (piping) , transverse plane , geology , scattering , geophysics , optics , chemistry , materials science , telecommunications , radar , biochemistry , structural engineering , computer science , engineering , metallurgy
On a rotating, aspherical earth, coupling between spheroidal and toroidal seismic free oscillations is manifested in the time domain as a slow alternation of the oscillation envelope between the transverse and the radial and/or vertical motion components. Using a narrow‐band smooth envelope estimator, we have observed this behavior in data from the M S = 8.1 Macquarie Ridge earthquake of 5/23/89. Rotational coupling is the principal cause of mixed‐type coupling for f < 4.2 mHz. However, envelope perturbations consistent with mixed‐type coupling are observed for 0 S 38 ‐ 0 T 36 and 0 S 37 ‐ 0 T 35 , which do not couple through rotation, and couple only weakly through smooth upper mantle velocity models. Such envelope perturbations can bias estimates of modal Q , and suggest that scattering may play a role in the attenuation of long‐period surface waves.