Collaborative Research: Surface wave and body wave modeling of attenuation in the mantle transition zone

地球内部的地震图像？S在对地球？S的构造和动力学进行地球物理和地球化学模拟中发挥着核心作用。这些地震模型中的大多数包含波速的三维变化。由于波幅和光谱含量是衰减研究中的主要数据，需要比旅行时和相位延迟更复杂的解释，所以到目前为止，层析成像的进展慢于速度层析成像。除了固有的波衰减外，由于波速的空间梯度、散射体的存在和地震破裂过程，聚焦还会影响振幅。例如，上地幔低速带的性质、地幔中水合相的作用以及通过过渡带的物质流动的研究进展，关键取决于地震速度和衰减模型的可用性。由于波速受几个因素(温度、成分、熔体)的影响，对层析速度图像的稳健和独特的解释需要地幔中衰减结构的图像，理想的是具有可比较的空间分辨率。拟议工作的主要目的是在我们之前的模型的基础上开发一个新的全球尺度的上地幔波衰减模型。该模型将受到新的基模和更高模面波振幅的约束。值得注意的是，泛音数据集以前没有在衰减研究中使用过，并将允许解析过渡区。这项研究的一个重要组成部分是对聚焦对波幅影响的改进的理论和实际处理方法的研究，包括对全球剪切速度和衰减模型的同时反演。分辨率测试的关键组件？包括使用体波幅度和频谱的独立数据集以及真实的3-D合成进行模型询问。他们将研究P和SH谱、S和SS幅度以及区域波形数据在多大程度上可以与我们新的衰减模型相一致。他们还将使用SPECFE合成技术检验一些关键的理论近似

Seismic images of the Earth?s interior play a central role in the geophysical and geochemical modeling of the planet?s structure and dynamics. The majority of these seismic models contain three-dimensional variations in wave speed. Attenuation, or Q−1, tomography has so far progressed more slowly than velocity tomography because wave amplitudes and spectral content, which are the primary data in attenuation studies, require a more complex interpretation than traveltimes and phase delays. In addition to intrinsic wave attenuation, amplitudes are affected by focusing due to spatial gradients in wave speed, the presence of scatterers, and the earthquake rupture process.Progress in the research of, for example, the nature of the low-velocity zone in the upper mantle, the role of hydrous phases in the mantle, and material flow through the transition zone depends critically on the availablity of models of seismic velocity and attenuation. Because wave speed isinfluenced by several factors (temperature, composition, melt), robust and unique interpretations of tomographic velocity images require accompanying images of the attenuation structure in the mantle, ideally with comparable spatial resolution.The main thrust of the proposed work involves the development of a new 3-D global-scale model for wave attenuation in the upper mantle that builds upon our previous modeling. The model will be constrained by new fundamental-mode and higher-mode surface-wave amplitudes. Notably, the overtone data set has not been used in attenuation studies before and will allow resolution of the transition zone. An important component of this research is the investigation into improved theoretical and practical treatments for focusing effects on wave amplitude, including a simultaneous inversion for global shear-velocity and attenuation models. A critical component of ?resolution testing? involves model interrogation with independent data sets of body-wave amplitudes and spectra, and with realistic 3-D synthetics. They will investigate to what extent P and SH spectra, S and SS amplitudes, and regional waveform data can be reconciled with our new attenuation model. They will also examine a number of critical theoretical approximations using SPECFEM synthetics