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

地球的地震图像？地球内部在地球物理和地球化学模拟中起着核心作用？S结构和动力学。这些地震模型大多包含波速的三维变化。衰减，或Q&amp；#8722；到目前为止，层析成像的进展要比速度层析成像慢得多，因为作为衰减研究的主要数据，波幅和频谱含量需要比旅行时间和相位延迟更复杂的解释。除了固有波衰减外，振幅还受到波速空间梯度、散射体存在和地震破裂过程的聚焦的影响。例如，上地幔低速带的性质、地幔中含水相的作用以及通过过渡带的物质流动等研究的进展，在很大程度上取决于地震速度和衰减模型的可用性。由于波速受多种因素（温度、成分、熔体）的影响，层析速度图像的可靠和独特解释需要伴随地幔衰减结构的图像，理想情况下具有相当的空间分辨率。这项工作的主要内容是在我们之前的模型的基础上，开发一个新的上地幔波衰减的三维全球尺度模型。该模型将受到新的基模和高模表面波振幅的约束。值得注意的是，泛音数据集以前没有用于衰减研究，并且可以分辨过渡区。本研究的一个重要组成部分是研究对波幅聚焦效应的改进理论和实践处理，包括全球剪切速度和衰减模型的同时反演。的关键组成部分？分辨率测试?包括对体波振幅和光谱的独立数据集以及真实的三维合成物进行模型询问。他们将研究P和SH谱、S和SS幅值以及区域波形数据在多大程度上可以与我们的新衰减模型相一致。他们还将使用SPECFEM合成材料检查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