Understanding the influence of deep seismic mantle structures at the core-mantle boundary on intense magnetic flux regions

地球的磁场产生于外核，其特点是在许多时间尺度上发生变化。虽然在赤道附近存在向西移动的强磁通量区和反向磁通量斑块等短期变化，但在其他区域则维持长期稳定的强磁通量区。在北半球的西伯利亚和加拿大地下发现了两个高通量区域，据预测，北大西洋将出现第三个高通量区域。有一些共识认为，地球下地幔的结构是地球磁场的边界条件，以前，地震层析成像模型已经被用来理解地幔结构和地核动力学之间的相互作用。在本研究中，我们的目标是研究核幔界面附近的地幔结构，即核幔边界（CMB），目的是建立1)高通量区周围与周围地幔的地震速度对比，2)结构的延伸和各向异性，以及3)哪些矿物是结构的成分。在此之后，我们将在靠近CMB的选定点构建热导率和电导率图，这是核动力学数值模拟的必要边界条件。我们将集中研究四个区域：北半球的两个可见区域和一个建议的强磁通量区域（西伯利亚、加拿大和北大西洋），以及印度尼西亚下面的区域，赤道上的强磁通量斑块似乎开始迅速向西移动。我们将使用地震波和横波的地震反射，以及来自CMB附近结构的转换波（P-to- s和S-to-P），例如D ‘ ’区域的顶部，超低速度带和其他反射器。我们将提取地震属性，如振幅、波形、反射波的极性，并将其与综合建模数据进行比较。我们还将测量和模拟横波分裂，以研究我们探测反射的同一区域的各向异性。利用可能存在于最下层地幔的矿物，我们将利用它们的弹性参数并计算变形和结构，这将提供方向相关的速度。这些速度将用于计算地震波在反射器处的反射和透射系数以及各向异性特征。利用地震反射和分裂以及变形模型将使我们能够确定最可能用于所研究结构的矿物。在与DeepDyn的矿物物理小组的合作中，我们将提供CMB的热导率和电导率图，这些图反过来又可以用作DeepDyn内部岩心建模的边界条件。

The Earth's magnetic field, generated in the outer core, is characterized by variations on many time scales. While there are short-time variations such as westward moving intense flux areas near the equator and reverse flux patches, long-term stable areas of intense magnetic flux are sustained in other regions. Two of those intense high flux regions are found in the northern hemisphere, beneath Siberia and Canada and there is a prediction for a third one in the North Atlantic. There is some consensus that structure in the Earth's lower mantle presents a boundary condition for the Earth’s magnetic field and previously, seismic tomography models have been used to understand the interaction between mantle structure and core dynamics. In this proposal we aim to investigate mantle structure near the interface between core and mantle, i.e., the core-mantle boundary (CMB), with the intent to establish 1) the seismic velocity contrast to the surrounding mantle around high flux regions, 2) the extend and anisotropy of the structure, and 3) which minerals are constituents of the structures. Following this we will construct maps of thermal and electrical conductivity at selected spots close to the CMB which are a necessary boundary condition for the numerical modelling of core dynamics. We will concentrate on four regions: The two visible regions and one proposed region of intense magnetic flux in the northern hemisphere (Siberia, Canada and the North Atlantic) as well as the region beneath Indonesia where intense flux patches at the equator seem to start moving rapidly westwards. We will use seismic reflections of P- and S-waves as well as converted waves (P-to-S and S-to-P) off structures near the CMB, such as the top of the D" region, ultra-low velocity zones, and other reflectors. We will extract seismic attributes, such as amplitude, waveform, polarities of the reflected waves and compare these with synthetically modelled data. We will also measure and model shear wave splitting to study anisotropy in the same regions where we detect reflections. Using minerals that are likely present in the lowermost mantle, we will use their elastic parameters and calculate deformation and texture, which will provide directionally dependent velocities. These velocities will then be used to calculate reflection and transmission coefficients of seismic waves at the reflectors and anisotropic characteristics. Using seismic reflections and splitting together with the deformation modelling will allow us to determine the most likely mineral for the investigated structure. In a collaboration with mineral physics groups in DeepDyn, we will then provide maps of thermal and electrical conductivities at the CMB which in turn can then be used as boundary condition for core modelling within DeepDyn.