Collaborative Research: Bayesian Estimation of Mantle Viscosity Structure and Geodynamic Implications

合作研究：地幔粘度结构的贝叶斯估计及其地球动力学意义

• 批准号: 1622464
• 负责人: Maxwell Rudolph
• 金额: $ 19.3万
• 依托单位: Portland State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2018-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1622464&HistoricalAwards=false
• 关键词: Collaborative; Research; Bayesian; Estimation; Mantle

Earth's mantle comprises more than 80% of our planet's interior, and convection in the mantle is linked to plate tectonics, the magnetic field, volcanic activity, and the gases in our atmosphere. Solid mantle rocks deform and flow over long time scales, and the viscosity (resistance to flow) of mantle rocks affects the rate of flow in the mantle, the energy budget of Earth's deep interior, and the speed with which tectonic plates move past one another. One of the best constraints on the mantle viscosity structure comes from modeling variations in Earth's long-wavelength gravity field. The team will combine mantle flow models, seismic images of the Earth's interior, and results from mineral physics to better constrain the depth variation of viscosity and its influence on mantle convection. The project will address the following scientific questions: (1) How does viscosity vary with depth, (2) How does viscosity structure affect behavior of buoyant, upwelling mantle material, and (3) How does uncertainty in seismic images of Earth's mantle affect our uncertainty in the viscosity profile? In addition to this research, the project contributes to the training and professional development of a graduate student and a postdoctoral researcher. Additionally, the team will work with a Portland-area high school teacher to develop curricular materials to teach concepts related to flow in the mantle from the Next Generation Science Standards.Full waveform whole-mantle tomography has recently provided improved measurements of lower mantle shear wave velocity anomalies. These images shed new light on the behavior of mantle upwellings and downwellings. Wide plumes, continuous from just above the core mantle boundary to the base of the lithosphere, are resolved beneath many of Earth's active volcanic hot spots, and plumes frequently appear to be deflected laterally below the transition zone, at a depth of 1000 km, a depth not coincident with known seismic discontinuities, but at which slabs stagnate, plumes are deflected, and changes in long-wavelength radial correlation structure appear in many tomographic models. Tomographic studies combining whole-Earth free oscillations with various other seismological observations (e.g. body wave travel times, surface wave dispersion, full waveforms) have recently improved constraints on the long-wavelength variations in wavespeed in the transition zone and mid mantle. Recent seismological data sets also suggest a deviation from simple scaling relationships between density and shear velocity, indicative of large-scale chemical heterogeneity in the lowermost mantle. The investigators will identify robust aspects of recent tomographic models, estimate uncertainties associated with their translation to density variations and employ a new inversion technique that incorporates these results in a probabilistic way to obtain improved constraints on the mantle viscosity structure. They will then use the solutions as the basis for numerical mantle convection simulations to evaluate the extent to which the inferred viscosity structures are compatible with available constraints on the style of convection and rate of heat transport in the mantle. In addition to training and mentoring of a graduate student and a postdoctoral researcher, the investigating team will work with a high school educator to develop curricular materials relevant to the Next Generation Science Standard HS-ESS2-3.

地球的地幔占我们星球内部的80％以上，地幔中的对流与板块构造，磁场，火山活动和我们大气中的气体有关。固体地幔岩石在长时间尺度上变形和流动，地幔岩石的粘度（对流动性）会影响地幔中的流量速率，地球深内部的能量预算以及构造板的速度相互移动。地幔粘度结构的最佳约束之一是对地球长波长重力场的建模变化。该团队将结合地幔流模型，地球内部的地震图像，并从矿物质物理学中结合粘度的深度变化及其对地幔对流的影响。该项目将解决以下科学问题：（1）粘度随深度的变化，（2）粘度结构如何影响浮力，上升的地幔材料的行为，以及（3）地球地震的地震图像中的不确定性如何影响我们在粘度概况中的不确定性？除了这项研究外，该项目还为研究生和博士后研究员的培训和专业发展做出了贡献。此外，该团队将与波特兰地区的高中老师合作，​​开发课程材料，以教授与下一代科学标准相关的概念。FullWave Wove Form Gull-Mantle phsographich最近提供了改进的低地幔剪切波速度的测量值。这些图像对地幔上升植物和下林的行为开辟了新的启示。 Wide plumes, continuous from just above the core mantle boundary to the base of the lithosphere, are resolved beneath many of Earth's active volcanic hot spots, and plumes frequently appear to be deflected laterally below the transition zone, at a depth of 1000 km, a depth not coincident with known seismic discontinuities, but at which slabs stagnate, plumes are deflected, and changes in long-wavelength径向相关结构出现在许多断层扫描模型中。层析成像研究结合全地球的自由振荡与其他各种地震学观察结果（例如，身体波旅行时间，表面波分散，完整波形）最近改善了对过渡区和中间通风中波动的长波长变化的约束。最近的地震学数据集还表明，密度和剪切速度之间的简单缩放关系偏离，这表明最低地幔中的大规模化学异质性。研究人员将确定近期层析成像模型的强大方面，估计与将其转换为密度变化相关的不确定性，并采用一种新的反转技术，以概率的方式结合这些结果，以获得对地幔粘度结构的改进约束。然后，他们将使用解决方案作为数值对流模拟的基础，以评估推断出的粘度结构与地幔中对流风格和热传输速率的可用约束。除了培训和指导研究生和博士后研究人员外，调查团队还将与高中教育者合作开发与下一代科学标准HS-ESS2-3相关的课程材料。