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建模中发挥着核心作用？的结构和动力。这些地震模型中的大多数包含波速的三维变化。衰减，或Q& #8722; 1，层析成像到目前为止比速度层析成像进展得更慢，因为作为衰减研究中的主要数据的波振幅和谱内容需要比走时和相位延迟更复杂的解释。除了本征波的衰减外，由于波速的空间梯度、散射体的存在和地震破裂过程等引起的聚焦也会影响振幅。例如，上地幔低速带的性质、地幔中含水相的作用、而通过过渡带的物质流主要取决于地震波速度和衰减模型的可用性。由于波的速度isaffected几个因素（温度，成分，熔体），强大的和独特的解释层析速度图像需要伴随的图像中的地幔衰减结构，理想情况下具有可比的空间resolution.The主要推力所提出的工作涉及一个新的3-D全球尺度模型的发展，在上地幔波衰减，建立在我们以前的建模。该模型将受到新的基本模式和更高模式的面波振幅。值得注意的是，泛音数据集以前没有用于衰减研究，将允许过渡区的分辨率。这项研究的一个重要组成部分是调查改进的理论和实践治疗聚焦波振幅的影响，包括全球剪切速度和衰减模型的同时反演。一个关键的组成部分？分辨率测试？涉及模型询问与体波振幅和频谱的独立数据集，并与现实的3-D合成。他们将研究P和SH谱、S和SS振幅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协调。他们还将研究一些关键的理论近似使用SPECFEM合成

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