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，为了解地球深部的组成和动力学提供了重要的见解。地震学数据已被用来建立地幔模型，但通常用于这种目的的数据(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设地震波速变化与密度变化线性相关而得到的。这一假设大致可以解释为纯热源引起的三维变化。然而，最近的研究结果表明，地幔内部的密度不均匀与横波速度异常的相关性很差，特别是在下地幔。在这个项目中，我们结合了多学科数据类型，以更好地约束地幔的属性，重点放在密度上。现代化的、密集的全球GPS站点将用于确定潮汐频率频谱上的固体潮振幅，以产生对(三维)乐夫数的位置相关校正。以前使用其他陆基空间大地测量系统的研究表明，GPS网络对勒夫数非常敏感，部分原因是潮汐的独特时间谱。这些勒夫数通常使用球对称的地球模型来计算。拟议的研究将探索一种方法，将全球大地测量数据和地震数据结合起来，产生一种新的地球机械结构模型。来自以前研究的地震学数据(正常模式分裂信息)、使用全球定位系统(GPS)站点网络的新大地测量的三维固体地球潮汐振幅以及来自卫星大地测量的地球重力场将被联合反演，以获得关于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敏感性和固有的分辨率，组合将导致相对于单独的技术具有更高的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.