Elasticity and rheology of iron above 220 GPa and the nature of the Earth's inner core
Elasticity and rheology of iron above 220 GPa and the nature of the Earth's inner core
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DOI：
10.1038/25506
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发表时间：
1998
期刊：
影响因子：
64.8
通讯作者：
H. Mao;J. Shu;G. Shen;R. Hemley;Baosheng Li;Anil K. Singh
中科院分区：
文献类型：
--
作者：
H. Mao;J. Shu;G. Shen;R. Hemley;Baosheng Li;Anil K. Singh
最近的数值模拟和地震学结果提出了关于地核动力学和磁性的新问题。了解铁在堆芯压力下的弹性和结构，对于理解地震观测结果，如地震波的低衰减、低剪切波速度和压缩波速度的各向异性，是至关重要的。六方密排铁的密度和体积模量以前已经用静态和动态方法测量到堆芯压力。在这里，我们研究，使用径向X射线衍射和超声波技术，剪切模量，单晶弹性张量，总的压缩和剪切波速度，以及这些速度在铁的取向依赖性。内核剪切波速度低于铁的总剪切波速度，表明存在低速组件或滞弹性效应的核心。铁样品中强晶格应变各向异性的观测表明，在等应力假设下，压缩波各向异性很大（约24%），因此不需要完美的晶体排列来解释地震观测。或者，应变各向异性可以指示由于优选的滑移系统而引起的应力变化。
Recent numerical-modelling and seismological results have raised new questions about the dynamics, and magnetism, of the Earth's core. Knowledge of the elasticity and texture of iron, at core pressures is crucial for understanding the seismological observations, such as the low attenuation of seismic waves, thelow shear-wave velocity, and the anisotropy of compressional-wave velocity,,. The density and bulk modulus of hexagonal-close-packed iron have been previously measured to core pressures by static and dynamic, methods. Here we study,using radial X-ray diffraction and ultrasonic techniques, the shear modulus, single-crystal elasticity tensor, aggregate compressional- and shear-wave velocities, and orientation dependence of these velocities in iron. The inner core shear-wave velocity is lower than the aggregate shear-wave velocity of iron, suggesting the presence of low-velocity components or anelastic effects in the core. Observation of a strong lattice strain anisotropy in iron samples indicates a large (∼24%) compressional-wave anisotropy under the isostress assumption, and therefore a perfect alignment of crystals would not be needed to explain the seismic observations. Alternatively the strain anisotropy may indicate stress variation due to preferred slip systems.