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arXiv 0803.0264physics.geo-ph
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地震波速度和衰减的多次散射模拟对最上部内核中grain size和稳定铁相的约束

Constraints on grain size and stable iron phases in the uppermost Inner Core from multiple scattering modeling of seismic velocity and attenuation

Marie Calvet, Ludovic Margerin

摘要:

我们建议将最上面的内核建模为随机取向的各向异性"补丁“的集合。一个补丁被定义为一个可能大量的晶体具有相同取向的晶轴的集合体。这个简单的模型解释了观测到的短周期体波的速度各向同性,并为在内核顶部探测到的散射体提供了合理的物理解释。通过对地震波在集料中传播的多次散射模型的严格模拟,我们得到了铁片的尺寸和弹性常数的强约束。我们进行了系统的搜索与测得的地震速度和衰减兼容的铁模型。铁模型的特征在于它的对称性(立方或六边形),弹性常数和补丁大小。独立的晶体对称性,我们推断最有可能的大小补丁的顺序为400米。最近的{ \it bcc}铁模型从文献中发现的立方晶体的最可能的弹性常数在我们的反演非常好的协议。我们的研究(1)表明,熔体的存在可能不需要解释低剪切波速度在内核和(2)支持最近的实验结果立方铁的稳定性在内核,至少在其上部。

英文摘要:

We propose to model the uppermost inner core as an aggregate of randomly oriented anisotropic ``patches''. A patch is defined as an assemblage of a possibly large number of crystals with identically oriented crystallographic axes. This simple model accounts for the observed velocity isotropy of short period body waves, and offers a reasonable physical interpretation for the scatterers detected at the top of the inner core. From rigorous multiple scattering modeling of seismic wave propagation through the aggregate, we obtain strong constraints on both the size and the elastic constants of iron patches. We perform a systematic search for iron models compatible with measured seismic velocities and attenuations. An iron model is characterized by its symmetry (cubic or hexagonal), elastic constants, and patch size. Independent of the crystal symmetry, we infer a most likely size of patch of the order of 400 m. Recent {\it bcc} iron models from the literature are in very good agreement with the most probable elastic constants of cubic crystals found in our inversion. Our study (1) suggests that the presence of melt may not be required to explain the low shear wavespeeds in the inner core and (2) supports the recent experimental results on the stability of cubic iron in the inner core, at least in its upper part.

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