An analysis of upper mantle discontinuity structure using 3D synthetics and global network data

使用 3D 合成和全球网络数据分析上地幔不连续结构

• 批准号: 1416695
• 负责人: Jeroen Ritsema
• 金额: $ 25.81万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1416695&HistoricalAwards=false
• 关键词: analysis; upper; mantle; discontinuity; structure

Radioactive decay of naturally occurring isotopes (e.g., uranium, thorium and potassium) has been a major source of Earth's internal heat throughout geologic time. This heat escapes primarily by slow (inches per year) convection in Earth's mantle. These currents are responsible for geologic activity including mountain building, volcanic eruptions, and earthquakes. While plate tectonics is the surface expression of solid-state rock flow in the mantle, it is still uncertain whether separate convection cycles exist in the upper and lower mantle (i.e., layered convection) or whether convection encompasses the entire mantle (i.e. whole-mantle convection). An understanding of mantle convection is important for modeling the thermal evolution of our planet.The proposed work is focused on boundaries near 410 km and 660 km. At the 410-km and 660-km boundaries, the most abundant rock-forming minerals undergo phase transitions to denser structures. Since the 410-km and 660-km mineral phase transitions depend on the ambient mantle temperature, precise maps of the depths of the 410-km and 660-km transitions act as 'thermometers' of the mantle and can be used to infer the scales of mantle flow. To date, the most precise global maps of the depths of the 410-km and 660-km transitions have been derived from the processing of seismic wave reflections produced by thousands of earthquakes and recorded by global arrays of seismometers. However, the latest maps produced by various research groups remain inconsistent. They exhibit different predominance of long-wavelength versus short-wavelength variations and major anomalies (i.e., thick and thin transition zone regions) are located incoherently. We will address these inconsistencies by investigating artifacts due to systematic data processing errors and ignored effects from 3D wave propagation in the heterogeneous mantle. Using state-of-the-art software for 3D seismic wave propagation, we will estimate the uncertainties in the applied analytical procedures, and we will determine the expected 410-km and 660-km topography for a range of convection scenarios for the mantle.

自然存在的同位素（例如铀，th和钾）的放射性衰变一直是整个地质时间内地球内部热量的主要来源。这种热量主要是由于地球地幔中的缓慢（每年英寸）对流而逃脱。这些电流负责地质活动，包括山区建筑，火山喷发和地震。虽然板块构造是地幔中固态岩石流动的表面表达，但仍不确定上层和下地幔中是否存在单独的对流周期（即分层对流），或者对流是否包含整个地幔对流）。对地幔对流的理解对于建模地球的热演化很重要。拟议的工作集中在接近410 km和660 km的边界上。在410公里和660公里的边界上，最丰富的岩石形成矿物经历了相变向密集的结构。由于410公里和660公里的矿物相转变取决于环境地幔温度，因此410公里的深度和660公里转变的精确地图充当地幔的“温度计”，可用于推断尺度地幔流。迄今为止，最精确的410公里和660公里过渡的深度的全局地图源自数千层地震产生的地震波反射的处理，并由全球阵列的地震仪记录。但是，各个研究小组制作的最新地图仍然不一致。它们表现出不同的长波长与短波长变化以及主要异常（即厚而薄的过渡区区域）的不同占主导地位。由于系统的数据处理错误，我们将通过研究伪影来解决这些矛盾，并忽略了异质地幔中3D波传播的影响。使用最先进的软件进行3D地震波传播，我们将估计应用分析程序中的不确定性，并将确定预期的410公里和660公里的地形，以范围内的一系列对流场景。