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.

在整个地质时期，自然产生的同位素(如铀、钍和钾)的放射性衰变一直是地球内部热量的主要来源。这些热量主要通过地幔中缓慢的对流(每年几英寸)散失。这些洋流导致了包括造山、火山喷发和地震在内的地质活动。虽然板块构造是地幔中固体岩流的表面表达，但仍然不确定上、下地幔是否存在单独的对流循环(即分层对流)，或者对流是否围绕整个地幔(即全地幔对流)。了解地幔对流对于模拟地球的热演化很重要。建议的工作主要集中在410公里和660公里附近的边界。在410公里和660公里的边界上，最丰富的造岩矿物经历了向更致密结构的相变。由于410千米和660千米矿物相变取决于周围的地幔温度，410千米和660千米矿物相变深度的精确地图充当了地幔的“温度计”，可以用来推断地幔流动的规模。迄今为止，410公里和660公里过渡深度的最精确全球地图是通过处理数千次地震产生的地震波反射得出的，并由全球地震仪阵列记录。然而，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和短波变化优势，主要异常(即厚、薄过渡带区)位置不一致。我们将通过调查由于系统数据处理错误和忽略了3D波在非均匀地幔中传播的影响而产生的伪影来解决这些不一致的问题。使用最先进的三维地震波传播软件，我们将估计应用的分析程序中的不确定性，并将确定一系列地幔对流情景的预期410公里和660公里的地形。