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

确定地幔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，为深入了解地球内部的组成和动力学提供了重要的见解。地震资料已被用来建立地幔模型，但通常用于此目的的数据（体波和面波）对密度变化不敏感。全球密度模型通常通过作出地震波速度变化与密度变化线性相关的强假设来获得。这个假设可以粗略地转换为纯粹热源引起的三维变化。然而，最近的研究结果表明，地幔内的密度不均匀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，我们结合联合收割机多学科的数据类型，以更好地约束地球的地幔属性，重点是密度。现代的，密集的，全球定位系统的网站将被用于确定整个潮汐频率的频谱的地球潮汐振幅，以产生网站相关的修正（三维）的爱数。以前的研究使用其他地基空间大地测量系统表明，GPS网络有很大的敏感性的勒夫数，部分原因是由于独特的时间频谱的潮汐。这些勒夫数通常使用球对称地球模型计算。拟议的研究将探索一种方法，将全球大地测量和地震数据结合起来，以产生一个新的地球力学结构模型。以往研究的地震数据（简正波分裂信息）、利用全球定位系统全球网络新的大地测量方法得出的三维固体-地球潮汐振幅以及卫星大地测量得出的地球重力场将联合反演，以获得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具有不同的灵敏度和固有分辨率，并且组合将导致相对于单独的技术具有上级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.