Plate tectonics and aspherical earth structure: The Importance of poloidal‐toroidal coupling
Plate tectonics and aspherical earth structure: The Importance of poloidal‐toroidal coupling
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板块构造和非球形地球结构：极向-环形耦合的重要性
DOI：
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发表时间：
1987
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影响因子：
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通讯作者：
W. Peltier
中科院分区：
文献类型：
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作者：
A. Forte;W. Peltier
我们推导出极向流内部加载绿色函数的不可压缩流体模型的地幔组成的一个单一的恒定粘度的球壳或两个相邻的球壳具有不同的粘度。根据绿色函数，我们得到了将地表散度场、大地水准面场和地表地形场与基于地震层析成像技术的应用推断的横向密度不均匀性相联系的核，并且利用这些核，我们认为，由调和度2-5组成的地表散度场和大地水准面场，在1200 km深度处，粘度增加系数仅为8。然而，我们指出，耦合从极向环向流，这是需要了解表面速度谱，可以让这些意见被理解在深度的粘度增加，这是小于所需的非流体静力大地水准面数据的背景下，纯极向模型。利用观测到的板块运动动能作为约束条件，可以推断上地幔的稳态粘滞系数为（2.0 ± 0.5）× 10 ~（21）Pa·s。本文对这一数值与根据对冰川均衡调整过程的特征分析而得出的稍低的数值（1 × 1021 Pa·s）之间的差异的含义作了评论。
We derive poloidal flow internal loading Green functions for incompressible fluid models of the mantle consisting either of a single constant viscosity spherical shell or of two adjacent spherical shells having different viscosities. From the Green function we obtain kernels connecting the surface divergence, the geoid, and the surface topography fields to the lateral density heterogeneity inferred on the basis of the application of seismic tomographic imaging techniques, and with these kernels we argue that both the surface divergence and geoid fields, consisting of harmonic degrees 2–5, may be reasonably fit with only a factor of 8 viscosity increase at a depth of 1200 km. We point out, however, that the coupling from poloidal to toroidal flow which is required to understand surface velocity spectra, may allow these observations to be understood in terms of a viscosity increase at depth which is smaller than required by nonhydrostatic geoid data in the context of pure poloidal models. Using the observed kinetic energy in the surface plate motions as a constraint allows us to infer a value for the steady state upper mantle viscosity of (2.0 ± 0.5) × 1021 Pa s. We comment on the implication of the difference between this number and the somewhat lower value (1 × 1021 Pa s) which has been derived on the basis of analyses of signatures of the glacial isostatic adjustment process.