CSEDI: Ultra-High Velocity Zones (UHVZs) at the core-mantle boundary

接近半个地球中心，2900公里深，是岩石地幔和富含熔铁的外核之间的分界线。在那里，在核-地幔边界(CMB)，最近在地幔一侧观察到了大小为数十公里的小型神秘结构。中巴是一条关键的界线。地幔物质从地核带走的热量为地球磁场提供能量，使我们免受太阳风的影响。驱动板块构造和相关灾害的地幔热对流可能为CMB带来了独特的物质；可能是地壳和上地幔的大片区域。确定新观测到的结构的特征很重要，因为它们包含了关于行星动力学、化学演化和现代状态的线索。在这里，研究人员使用地震学--研究地震波在地球内的传播--来成像和描述这些结构。它们被称为超高速带，因为穿过它们的地震波表现出非常高的速度。为了确定它们的起源，该团队使用地球动力学模型研究了地幔的对流特性。研究人员还进行了实验和计算计算，以研究在地幔深处极端压力和温度下候选物质的性质。这些数据有助于约束和解释地震观测，揭开了超高速带性质的面纱。该项目为一名初出茅庐的科学家、一名博士后助理和两名女研究生提供支持。它还促进对本科生的培训，并在每年的活动中通过互联网向公众宣传教育。这一多学科项目涵盖了超高速区域(UHVZ)的探测、成像、建模和表征。该团队的初步工作是在科科斯和加勒比海构造板块下方的地点发现它们，该地区位于过去和现在活跃的俯冲带之下。研究人员专注于绘制和模拟那里和其他地理位置的UHVZ，分析从地核反射出来的地震波(称为ScS波、SCP波和PCP波)。此外，他们还通过进行高压实验和计算来探索成分的可能性。这些包括从上方引入的物质，如俯冲的洋壳和沉积物，以及从下方(核-地幔相互作用)引入的物质。在同步加速器国家设施中，利用多台顶压机和金刚石-顶压室装置对矿物的相关系和性质进行了实验研究。他们探索了大范围的压力，最高可达135 Gpa(约130万大气压)的极端压力，普遍存在于地幔最下部。实验与计算相结合，得到了预期速度的估计，并与地震学结果进行了比较。同时，地球动力学模拟研究来自俯冲或CMB的成分输入的动力学行为。这为指导实验工作以及地震观测的解释和模拟提供了一个框架。超高温区可能对许多深部地幔现象产生重要影响，包括地核和地幔之间的热量和化学交换。它们可能与以前记录的超低速带和/或热化学堆原点的重要地球动力学旋回有关。研究新发现的CMB结构可能会为更大规模的过程提供见解，如全地幔对流和地幔化学的演化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nearly half way to the center of the Earth, 2900 km deep, lies the boundary between the rocky mantle and the molten iron-rich outer core. There, at the core-mantle boundary (CMB), small enigmatic structures of tens of km in size were recently observed on the mantle side. The CMB is a critical boundary. The heat conducted away from the core by mantle materials contributes to power the Earth's magnetic field which shields us from the solar wind. Mantle thermal convection, which drives plate tectonics and associated hazards, might have brought unique materials to the CMB; possibly large sections of the Earth's crust and upper mantle. Characterizing the newly observed structures is important, because they hold clues on the planet dynamics, chemical evolution and present-day state. Here, the researchers use seismology - the study of seismic-wave propagation within the Earth - to image and characterize these structures. They are called ultra-high velocity zones, because seismic waves passing through them exhibit remarkably high velocities. To identify their origins, the team studies the convective properties of the mantle using geodynamic modeling. The researchers also carry out experiments and computational calculations to investigate the properties of candidate materials at the extreme pressure and temperature of the deep mantle. These data help to constrain and interpret seismic observations, lifting the veil on the nature of ultra-high velocity zones. This project provides support to an early-career scientist, a postdoctoral associate and two female graduate students. It also promotes training for an undergraduate student and educational outreach to the public at yearly events and via the internet. This multidisciplinary project frames the detection, imaging, modeling, and characterization of ultra-high velocity zones (UHVZs). The team's preliminary work finds them in spots beneath the Cocos and Caribbean tectonic plates, a region located beneath past and present active subduction zones. The researchers focus on mapping and modeling UHVZs there and in other geographical locales, analyzing seismic waves that reflects off of Earth's core (named ScS, ScP, and PcP waves). In addition, they explore compositional possibilities by performing high-pressure experiments and calculations. These involve materials introduced from above, such as subducted ocean crust and sediments, and from below (core-mantle interactions). Experiments on phase relations and properties of minerals are carried out using multi-anvil press and diamond-anvil cell setups at synchrotron national facilities. They explore a large range of pressure, up to the extreme pressure of 135 GPa (~1.3 million atm) prevailing in the lowermost mantle. Experiments are combined with calculations leading to estimates of expected velocities, which are compared with seismological results. In parallel, geodynamic modeling investigates the dynamical behavior of compositional input from subduction or the CMB. This provides a framework guiding the experimental work and the interpretation and modeling of seismic observations. UHVZs may have important effects on a number of deep mantle phenomena, including heat and chemistry exchange between the core and mantle. They may relate to important geodynamical cycles at the origin of the previously documented ultra-low velocity zones and/or thermochemical piles. Investigating the newly discovered CMB structures may provide insights on larger scale processes, like whole mantle convection and the evolution of mantle chemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.