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Detailed Reference Information |
Cormier, V.F., Xu, L. and Choy, G.L. (1998). Seismic attenuation of the inner core: Viscoelastic or stratigraphic?. Geophysical Research Letters 25: doi: 10.1029/1998GL900074. issn: 0094-8276. |
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Broadband velocity waveforms of PKIKP in the distance range 150¿ to 180¿ are inverted for inner core attenuation. A mean Q&agr; of 244 is determined at 1 Hz from 8 polar and 9 equatorial paths. The scatter in measured Q-1 exceeds individual error estimates, suggesting significant variation in attenuation with path. These results are interpreted by (1) viscoelasticity, in which the relaxation spectrum has a low-frequency corner near or slightly above the frequency band of short-period body waves, and by (2) stratigraphic (scattering) attenuation, in which attenuation and pulse broadening are caused by the interference of scattered multiples in a velocity structure having rapid fluctuations along a PKIKP path. In the scattering interpretation, PKIKP attenuation is only weakly affected by the intrinsic shear attenuation measured in the free-oscillation band. Instead, its frequency dependence, path variations, and fluctuations are all explained by scattering attenuation in a heterogeneous fabric resulting from solidification texturing of intrinsically anisotropic iron. The requisite fabric may consist of either single or ordered groups of crystals with P velocity differences of at least 5% and as much as 12% between two crystallographic axes at scale lengths of 0.5 to 2 km in the direction parallel to the axis of rotation and longer in the cylindrically radial direction, perpendicular to the axis of rotation. ¿ 1998 American Geophysical Union |
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Abstract |
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Keywords
Physical Properties of Rocks, Wave attenuation, Seismology, Body wave propagation, Seismology, Core and mantle, Tectonophysics, Earth's interior—composition and state |
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Publisher
American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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