Seismic attenuation of the inner core: Viscoelastic or stratigraphic?
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Abstract
Broadband velocity waveforms of PKIKP in the distance range 150° to 180° are inverted for inner core attenuation. A mean Qα 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.
Publication type | Article |
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Publication Subtype | Journal Article |
Title | Seismic attenuation of the inner core: Viscoelastic or stratigraphic? |
Series title | Geophysical Research Letters |
DOI | 10.1029/1998GL900074 |
Volume | 25 |
Issue | 21 |
Year Published | 1998 |
Language | English |
Publisher | American Geophysical Union |
Description | 4 p. |
First page | 4019 |
Last page | 4022 |
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