Collaborative Research: Combined Seismological and Geodetic Constraints on 3-D Mantle Structure

确定地幔的结构是地球物理研究的一个基本问题。这些信息，特别是密度的变化，为了解地球深处的组成和动态提供了重要的见解。地震数据已被用于构建地幔模型，但通常用于此目的的数据（体波和面波）对密度变化不敏感。全球密度模型通常是通过假定地震波速度变化与密度变化呈线性关系而得到的。这个假设可以粗略地解释为纯热源引起的三维变化。然而，最近的研究结果表明，地幔内部的密度非均质性与剪切波速度异常的相关性很差，特别是在下地幔。在这个项目中，我们将多学科数据类型结合起来，以更好地约束地球地幔的特性，重点关注密度。现代的、密集的全球GPS站点将用于确定潮汐频率频谱上的潮汐振幅，从而对（三维）Love数字进行基于站点的修正。以往使用其他地基空间大地测量系统的研究表明，GPS网络对洛夫数非常敏感，部分原因是潮汐的独特时间谱。这些爱的数字通常是用一个球对称的地球模型来计算的。拟议的研究将探索一种结合全球大地测量和地震数据的方法，以产生地球机械结构的新模型。将前人研究的地震数据（正态分裂信息）、利用全球定位系统（GPS）站点网络的新大地测量解得到的三维固体地球潮汐幅值以及卫星大地测量得到的地球重力场联合反演，得到地幔弹性参数和密度的三维模型。这些数据类型中的每一种都有不同的灵敏度和固有的分辨率，它们的组合将导致一个相对于单个技术具有更高精度和分辨率的模型。

Determining the structure of the Earth's mantle is a fundamental problem of geophysical research. This information, especially the variation in density, provides important insight into the composition and dynamics of the Earth's deep interior. Seismological data have been used to construct models of the mantle, but the data conventionally used for such purpose (body and surface waves) are not sensitive to density variation. A global density model is typically obtained by making a strong assumption that seismic wave speed variations are linearly related to density variation. This assumption loosely translates to three-dimensional variations arising from a purely thermal origin. Results from recent studies, however, suggest that the density heterogeneity within the mantle is poorly correlated with shear-wave speed anomalies, especially in the lower mantle. In this project, we combine multidisciplinary data types to better-constrain properties of the Earth's mantle with a focus on density. The modern, dense, global GPS sites will be used for the determination of Earth-tide amplitudes across the spectrum of tidal frequencies to yield site-dependent corrections to the (three-dimensional) Love numbers. Previous studies using other ground-based space geodetic systems indicate that the GPS network has great sensitivity to the Love numbers, in part due to the unique temporal spectrum of the tides. These Love numbers are usually calculated using a spherically symmetric Earth model. The proposed research would explore an approach for combining global geodetic and seismic data to yield a new model for the mechanical structure of the Earth. Seismological data (normal mode splitting information) from previous studies, three-dimensional solid-Earth tidal amplitudes from a new geodetic solution using a global network of Global Positioning System (GPS) sites, and the Earth's gravity field from satellite geodesy will be jointly inverted to obtain a three-dimensional model for the elastic parameters and density of the mantle. Each of these data types has different sensitivities and inherent resolution, and the combination will lead to a model with superior accuracy and resolution relative to the individual techniques.