Anisotropy of heterogeneity scale lengths in the lower mantle from PKIKP precursors

被引:45
作者
Cormier, VF [1 ]
机构
[1] Univ Connecticut, Dept Geol & Geophys, Storrs, CT 06269 USA
关键词
core-mantle boundary; mantle heterogeneity; scattering;
D O I
10.1046/j.1365-246X.1999.00736.x
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The anisotropy of heterogeneity scale lengths in the lower mantle is investigated by modelling its effect on the high-frequency precursors of PKIKP scattered by the heterogeneities. Although models having either an isotropic or an anisotropic distribution of scale lengths can fit the observed coda shapes of short-period precursors, the frequency content of broad-band PKIKP precursors favours a dominantly isotropic distribution of scale lengths. Precursor coda shapes are consistent with 1 per cent fluctuations in P velocity in the wavenumber band 0.05-0.5 km(-1) extending to 1000 km above the core-mantle boundary, and with a D " region open to circulation throughout the lower mantle. The level of excitation of PKIKP precursors observed in the frequency band 0.02-2 Hz requires a power spectrum of heterogeneity that is nearly white or slowly increasing with wavenumber. Anisotropy of scale lengths may exist in a D " layer having larger horizontal than Vertical scale lengths and produce little or no detectable effects on PKIKP precursors for P-velocity perturbations as high as 3 per cent when averaged over a vertical scale of several kilometres, and much higher when averaged over scales of hundreds of metres or less.
引用
收藏
页码:373 / 384
页数:12
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