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

了解核幔边界深部地震地幔结构对强磁通区域的影响

• 批准号: 521545943
• 负责人: Professor Dr. Joachim Ritter
• 金额: --
• 依托单位: Geophysikalisches Institut (GPI)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/521545943?language=en
• 关键词: Understanding; influence; deep; seismic; mantle

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.

地球外核产生的磁场具有在许多时间尺度上变化的特点。虽然有短期变化，如赤道附近向西移动的强磁通量区域和反向磁通量斑块，但在其他区域保持了长期稳定的强磁通量区域。其中两个强烈的高通量区域位于北半球西伯利亚和加拿大下方，预计第三个区域将出现在北大西洋。有一些共识认为，地球下地幔的结构为地球磁场提供了一个边界条件，以前，地震层析成像模型被用来理解地幔结构和地核动力学之间的相互作用。在这个方案中，我们旨在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)高通量地区与周围地幔的地震速度对比，2)结构的伸展和各向异性，3)哪些矿物是结构的组成部分。在此之后，我们将在CMB附近的选定地点绘制热导率和电导率图，这是对核心动力学进行数值模拟的必要边界条件。我们将集中在四个区域：北半球(西伯利亚、加拿大和北大西洋)的两个可见区域和一个拟议的强磁通量区域，以及印度尼西亚下方的区域，在那里赤道的强烈磁通量斑块似乎开始快速向西移动。我们将使用P波和S波以及转换波(P波到S波和S波到P波)在CMB附近的结构上的地震反射，如D“区顶部、超低速带和其他反射层。我们将提取地震属性，如反射波的幅度、波形、极性，并将这些属性与合成模型数据进行比较。我们还将测量和模拟横波分裂，以研究我们探测到反射的相同区域的各向异性。利用可能存在于地幔最下部的矿物，我们将使用它们的弹性参数，并计算变形和纹理，这将提供方向相关的速度。这些速度将被用来计算地震波在反射层的反射系数和透射率以及各向异性特征。使用地震反射和分裂以及形变模拟，将使我们能够确定所调查的构造最可能的矿物。然后，我们将与DeepDyn的矿物物理小组合作，提供CMB的热导率和电导性地图，这些地图随后可以用作DeepDyn内部岩芯建模的边界条件。