Dumberry Mathieu, Mandea Mioara
Department of Physics, University of Alberta, Edmonton, T6G 2E1 Canada.
Centre National d'Études Spatiales, 2 Place Maurice Quentin, 75039 Paris, France.
Surv Geophys. 2022;43(1):5-39. doi: 10.1007/s10712-021-09656-2. Epub 2021 Sep 30.
Fluid motion within the Earth's liquid outer core leads to internal mass redistribution. This occurs through the advection of density anomalies within the volume of the liquid core and by deformation of the solid boundaries of the mantle and inner core which feature density contrasts. It also occurs through torques acting on the inner core reorienting its non-spherical shape. These in situ mass changes lead to global gravity variations, and global deformations (inducing additional gravity variations) occur in order to maintain the mechanical equilibrium of the whole Earth. Changes in Earth's rotation vector (and thus of the global centrifugal potential) induced by core flows are an additional source of global deformations and associated gravity changes originating from core dynamics. Here, we review how each of these different core processes operates, how gravity changes and ground deformations from each could be reconstructed, as well as ways to estimate their amplitudes. Based on our current understanding of core dynamics, we show that, at spherical harmonic degree 2, core processes contribute to gravity variations and ground deformations that are approximately a factor 10 smaller than those observed and caused by dynamical processes within the fluid layers at the Earth's surface. The larger the harmonic degree, the smaller is the contribution from the core. Extracting a signal of core origin requires the accurate removal of all contributions from surface processes, which remains a challenge.
Dynamical processes in Earth's fluid core lead to global gravity variations and surface ground deformationsWe review how these processes operate, how signals of core origin can be reconstructed and estimate their amplitudesCore signals are a factor 10 smaller than the observed signals; extracting a signal of core origin remains a challenge.
地球液态外核内的流体运动导致内部质量重新分布。这是通过液态核体积内密度异常的平流以及地幔和内核具有密度差异的固体边界的变形来实现的。它还通过作用在内核上的扭矩使其非球形形状重新定向而发生。这些原位质量变化导致全球重力变化，并且为了维持整个地球的力学平衡，会发生全球变形（引发额外的重力变化）。由地核流动引起的地球自转轴矢量变化（以及因此的全球离心势变化）是全球变形和源自地核动力学的相关重力变化的另一个来源。在这里，我们回顾了这些不同的地核过程是如何运作的，如何重建来自每个过程的重力变化和地面变形，以及估计它们幅度的方法。基于我们目前对地核动力学的理解，我们表明，在球谐度数为2时，地核过程对重力变化和地面变形的贡献比地球表面流体层内的动力学过程所观测到的和引起的贡献小约一个数量级。谐波度数越大，地核的贡献越小。提取地核起源的信号需要准确去除表面过程的所有贡献，这仍然是一个挑战。
地球流体地核中的动力学过程导致全球重力变化和地表地面变形
我们回顾了这些过程如何运作，如何重建地核起源的信号并估计它们的幅度
地核信号比观测信号小一个数量级；提取地核起源的信号仍然是一个挑战。
