偏心内核的地球物理意义
Geophysical implications of a decentered inner core
摘要：
在第一近似中，地球内部具有球对称的各向同性结构。在过去的几十年里，地球物理观测揭示了在不同的空间尺度上，这种基本结构存在多种扰动。本文讨论了当内核偏离地球的质心时，这种基本结构所引起的半球扰动。利用数值模拟观测到的半球不对称的地震波通过上部内核，更快的到达时间和更高的衰减在东半球，我们估计，目前的位置的内核从地球中心向东移动了几十公里，在赤道平面。如果作用在内核上的力只有重力，那么它的平衡位置将在地球的中心，估计的位移将是不可能的。我们推测，由于与外核内部的流动和磁场的相互作用，内核处于永久的混沌运动。为了支持这一假设，我们分析了十多个不同的地球物理现象一致的内核运动占主导地位的时间尺度从几百年到几千年。
英文摘要：
In a first approximation, the Earth's interior has an isotropic structure with a spherical symmetry. Over the last decades the geophysical observations have revealed, at different spatial scales, the existence of several perturbations from this basic structure. In this paper we discuss the hemispheric perturbations induced to this basic structure if the inner core is displaced from the center of mass of the Earth. Using numerical simulations of the observed hemispheric asymmetry of the seismic waves traveling through the upper inner core, with faster arrival times and higher attenuation in the Eastern Hemisphere, we estimate that the present position of the inner core is shifted by tens of kilometers from the Earth's center eastward in the equatorial plane. If the only forces acting on the inner core were the gravitational forces, then its equilibrium position would be at the Earth's center and the estimated displacement would not be possible. We conjecture that, due to interactions with the flow and the magnetic field inside the outer core, the inner core is in a permanent chaotic motion. To support this hypothesis we analyze more than ten different geophysical phenomena consistent with an inner core motion dominated by time scales from hundreds to thousands of years.
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