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

自然产生的同位素（如铀、钍和钾）的放射性衰变在整个地质时期一直是地球内部热量的主要来源。这些热量主要通过缓慢（每年几英寸）的地幔对流逸出。这些洋流造成了地质活动，包括造山、火山爆发和地震。板块构造是地幔中固态岩石流动的表面表现，但上下地幔是否存在单独的对流旋回（即层状对流），对流是否包含整个地幔（即全地幔对流）仍不确定。了解地幔对流对于模拟地球的热演化非常重要。建议的工作重点是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密度更大的结构的相变。由于410公里和660公里的矿物相变依赖于周围的地幔温度，410公里和660公里的矿物相变深度的精确地图就像地幔的“温度计”，可以用来推断地幔流动的规模。迄今为止，最精确的410公里和660公里转换深度的全球地图，是通过处理数千次地震产生的地震波反射，并由全球地震仪阵列记录下来的。然而，不同研究小组绘制的最新地图仍然不一致。它们表现出长波长和短波长的不同优势，主要异常（即厚和薄过渡区）的位置不相干。我们将通过研究由于系统数据处理错误和在非均质地幔中被忽视的三维波传播的影响而产生的伪影来解决这些不一致。利用最先进的三维地震波传播软件，我们将估算应用分析过程中的不确定性，并确定地幔对流场景下410公里和660公里的预期地形。

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.