Variation in apparent attenuation of the Earth's normal modes due to lateral heterogeneity

Citation:
Davis, PJ.  1985.  Variation in apparent attenuation of the Earth's normal modes due to lateral heterogeneity. Geophysical Research Letters. 12:141-144., Washington, DC, United States (USA): American Geophysical Union, Washington, DC

Keywords:

19:Seismology, attenuation, discontinuities, Earth, elastic waves, free oscillations, horizontal discontinuities, motions, processes, Q, seismic waves, Seismology, theoretical studies, variations, velocity structure

Abstract:

Study of 3242 full first order synthetic seismograms of isolated normal mode multiplets shows that constructive and destructive interference of the singlets comprising a multiplet can account for the noise-corrected variance of free oscillation attenuation measurements in the frequency band 3.0-4.0 mHz. This interference gives rise to a distribution of synthetic Q measurements which is sensitive to the short wavelength velocity features of a model. While individual attenuation measurements depend also on the moment tensor, the overall variance of Q fluctuations is insensitive to the characteristics of the source employed and depends little on the length of the time series processed. The Woodhouse-Dziewonski model M84A of upper mantle velocity structure causes a scatter in the synthetics large enough to interfere significantly with any signal from lateral Q structure. Correlation of individual synthetics with data is poor, however, which suggests that either there are remaining uncertainties in the velocity model, that mode-mode coupling occurs in the data in a way that is poorly understood, or that lateral attenuative structure contributes to the observed scatter. Resolution of any such Q structure will be difficult given the present data set.

Notes:

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DOI:

10.1029/GL012i003p00141