Mapping elastic and anelastic structure in the global upper mantle

地球地幔的弹性和滞弹性地震结构提供了两个独立的地震学约束，需要区分温度和成分的不均匀性在地幔。地震面波观测已被用于绘制全球上地幔的弹性和滞弹性结构图，而目前不同研究小组所建立的滞弹性地球模型存在很大差异。 波的衍射效应，以及弹性和滞弹性地幔变化的面波观测值的双重依赖性仍然知之甚少，并没有适当地考虑到目前的表面波层析成像研究。本研究旨在更好地理解利用地震面波绘制地球弹性和滞弹性结构图的基本理论问题，发展超越传统方法的理论基础，并对全球上地幔三维弹性和滞弹性结构进行成像。 这项研究包括理论和观察两个部分。理论部分侧重于使用谱元法（SEM）在三维地球模型中进行全波传播模拟，以量化（1）三维弹性和滞弹性异常情况下表面波传播中的有限频率效应;（2）地震波走时和振幅对三维波速和三维滞弹性结构的双重依赖性，包括三维非弹性色散和振幅聚焦与散焦效应;（3）传统地震射线理论在利用走时和振幅数据进行联合层析反演时的分辨率局限性。本研究的观测部分包括：（1）利用多锥技术建立全球基模面波相位延迟和振幅测量数据集;（2）基于全球数据集同时反演全球上地幔三维速度和滞弹性（Q）结构。充分考虑了有限频率效应以及地震观测量对三维速度和三维Q结构的双重依赖性。

The elastic and anelastic seismic structure of the Earth's mantle provide two independent seismological constraints that are required to distinguish between temperature and compositional heterogeneities in the mantle. Seismic surface wave observations have been used to map the elastic and anelastic structure in the global upper mantle and large discrepancies exit among present-day anelastic earth models developed by different research groups. Wave diffractional effects, as well as the dual dependence of surface-wave observables upon elastic and anelastic variations in the mantle remain poorly understood and have not been properly taken into account in current surface wave tomographic studies. This research aims to better understand fundamental theoretical problems in mapping the earth's elastic and anelastic structure using seismic surface waves, develop theoretical foundations beyond traditional methods and to image the global 3-D elastic and anelastic structure in the upper mantle. This research includes both a theoretical and an observational component. The theoretical component focuses on full wave propagation simulations in 3-D earth models using the Spectral Element Method (SEM) to quantify (1) finite-frequency effects in surface wave propagation in the presence of 3-D elastic and anelastic anomalies; (2) the dual dependence of seismic traveltimes and amplitudes upon 3-D wavespeed and 3-D anelasticity structure, including 3-D anelastic dispersion and amplitude focusing and defocsuing effects and (3) resolution limitations of traditional seismic ray theory in joint tomographic inversions using traveltime and amplitude data. The observational component of this research includes (1) development of a global dataset of fundamental-mode surface-wave phase-delay and amplitude measurements using a multi-taper technique and (2) simultaneous inversion of 3-D velocity and anelasticity (Q) structure in the global upper mantle based upon the global dataset, fully accounting for finite-frequency effects as well as the dual dependence of seismic observables upon 3-D velocity and 3-D Q structure.