Simultaneous inversion for mantle conductivity and source field: towards a 3-d global reference model

虽然地幔电导率主要是径向增加与深度，越来越多的证据表明，有显着的横向不均匀性，在上地幔和中地幔，反映在成分，物理状态，温度和挥发分含量的变化。电导率补充了地震导出的密度和弹性参数;通过这些参数的共同登记和联合解释，可以更好地限制地球内部的组成和物理状态。该项目的目标是开发这些3D变化的显着改进的图像，特别是在过渡区和上地幔。该项目将数据分析的新方法与数值模拟和地球物理反演方法相结合。一种经验正交函数方法正在应用于地磁观测数据，以提取地球导电地幔在日变化和较长时期内的外部激励的主导模式。这些模式对应于最对称的大尺度源，然后通过同时调整外部源结构和三维地球电导率来拟合。在这种联合反演中的一个关键约束是物理上合理的外部源空间结构的先验知识。 这种结构是通过使用参数模型，并通过多变量空间协方差开发的源的几何形状和电离层大气环流模型的输出的知识来执行。共同注册的电气和弹性模型将是有用的地球动力学，分离更好的温度和成分的影响，在3-D层析成像，矿物物理学家开发的状态方程有关的地球深部物质。该研究还将改进外部源场的表征，这与3D电导率模型一起将对那些使用卫星磁数据的人非常有用，例如，以提供改进的外部/感应场校正，用于主场或地壳场的建模。 目前和计划中的利用磁卫星数据探测地幔电导率的工作特别依赖于改进外部来源的时空模拟，并将最终从该项目的结果中获益匪浅。该项目通过为一名职业生涯初期的女科学家提供博士后支持，促进下一代地球科学研究人员的多样性和培训。正在制作一个全球三维电导率参考模型，该模型将作为一种资源提供给广大的地球科学研究人员，例如，为区域大地电磁和地磁感应研究数据的建模和反演提供边界条件和大规模背景，包括EarthScope主干和可移动MT阵列。

Although mantle electrical conductivity primarily increases radially with depth, a growing body of evidence indicates there is significant lateral heterogeneity in the upper and mid-mantle, reflecting variations in composition, physical state, temperature, and volatile content. Conductivity complements seismically-derived density and elastic parameters; through co-registration and joint interpretation of these parameters, one can obtain better constraints on the composition and physical state of Earth's interior. The goal of this project is to develop significantly improved images of these 3D variations, especially in the transition zone and upper mantle. The project combines new approaches to data analysis with numerical modeling and geophysical inverse methods. An empirical orthogonal function approach is being applied to geomagnetic observatory data to extract the dominant modes of external excitation of the Earth's conducting mantle at daily variation and longer periods. These modes, which correspond to the most symmetric large scale sources, are then fit by simultaneously adjusting external source structure and 3-d Earth conductivity. A key constraint in this joint inversion is a priori knowledge of physically reasonable external source spatial structure. Such structure is enforced through use of parametric models, and through multivariate spatial covariances developed from knowledge of source geometries and outputs of ionospheric general circulation models. Co-registered electrical and elastic models will be useful to geodynamicists, to separate better temperature and compositional effects in 3-d tomographic images, and by mineral physicists developing equations of state relevant to deep Earth materials. The research will also result in an improved characterization of external source fields, which, together with the 3D conductivity model, will be very useful to those working with satellite magnetic data, e.g., to provide improved external/induced field corrections for modeling of the main or crustal fields. Current and planned efforts to use magnetic satellite data to probe mantle conductivity in particular depend critically on improved spatio-temporal modeling of external sources, and will ultimately benefit significantly from the results of this project. The project contributes to diversity and training of the next generation of Earth science researchers by providing post-doc support for an early-career female scientist. A global 3-d conductivity reference model is being produced that will be available as a resource to a broad community of Earth Science researchers, e.g., to provide boundary conditions, as well as large scale context, for modeling and inversion of data from regional magnetotelluric and geomagnetic induction studies, including the EarthScope backbone and transportable MT arrays.