CSEDI Collaborative Proposal: a multi-disciplinary investigation of slab deformation and resulting seismic anisotropy from the transition zone to the base of the mantle

在地质年代尺度上，地球内部深处的岩石像流体一样流动。地球内部岩石的变形和平流是地幔热对流的具体表现。地幔对流驱动着地球表面附近的板块构造，控制着地球的长期演化。在这个项目中，一组来自不同研究领域的科学家——包括地震学、矿物物理学和地球动力学——合作更好地了解地幔对流的本质。当地震发生时，能量以地震波的形式在地球内部传播。地震波在一个方向上穿过岩石的速度与在另一个方向上的速度往往不同。这种现象被称为地震各向异性。岩石的地震各向异性受其矿物结构和周围地幔流性质的控制。在这里，研究人员使用超级计算机模拟地幔流场。他们进行矿物物理实验，研究地幔矿物的变形机制。他们通过分析地震波来了解地幔地震各向异性。将预测的地幔流场与矿物变形的新认识相结合，预测地震各向异性，并与观测结果进行比较。其目的是为地球深处的结构和动力学提供新的见解。该项目促进跨学科合作，并为3名研究生，1名博士后和1名早期职业科学家提供支持。将编制教材，用于本科和研究生班，并通过外展活动和通过互联网向公众进行教育外展。分析和建模软件将提供给一般用户。在过去的几十年里，地震各向异性主要在地球的最上地幔和最下地幔被观测到。然而，越来越多的证据表明，在过渡带和上、下地幔存在显著的地震各向异性。上地幔地震各向异性的性质已经较为明确，对D”的大尺度各向异性分布有一定的一级共识。然而，对于地幔过渡带和上、下地幔地震各向异性的特征和强度，目前还没有一致的认识。在这些深度，地震各向异性与地幔流动和地幔矿物变形机制的关系尚不清楚。在地幔动力学背景下解释地震观测需要矿物物理学家和地球动力学家的投入；它们可以将地震速度和各向异性与相应材料的温度、成分和变形联系起来。在这里，一个由地震学家、地球动力学家和矿物物理学家组成的跨学科团队旨在进一步推进对两个区域的地震和粘度结构以及地幔流动性质的理解：1)D”层，继续他们以前的工作；(2)位于地球内部~400 ~ 1000 km深度的扩展过渡带。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Over geological time scales, rocks in Earth’s deep interior flow like fluids. The deformation and advection of rocks within the Earth are concrete expressions of mantle thermal convection. Mantle convection drives plate tectonics near Earth’s surface and controls the long-term evolution of the planet. For this project, a team of scientists from different research fields - including seismology, mineral physics, and geodynamics - collaborate to better understand the nature of mantle convection. When earthquakes happen, the energy propagates through Earth’s interior in the form of seismic waves. The speed of seismic waves traveling through rocks in one direction is often different from that in another direction. This phenomenon is called seismic anisotropy. Seismic anisotropy of rocks is controlled by their mineral structure and the nature of the surrounding mantle flows. Here, the researchers use super-computers to simulate mantle flow fields. They perform mineral physics experiments to study the deformation mechanisms of mantle minerals. They analyze seismic waves to understand mantle seismic anisotropy. The predicted mantle flow fields are combined with new understanding of mineral deformation to predict seismic anisotropy, which is then compared with observations. The aim is to provide new insight into the structure and dynamics of Earth’s deep interior. This project fosters inter-disciplinary collaboration and provides support to 3 graduate students, 1 postdoctoral associate and 1 early-career scientist. Teaching materials will be produced, which will be used in undergraduate and graduate classes and in educational outreach to the public through outreach events and via the internet. Analytical and modeling software will become available to general users.Over the past few decades, seismic anisotropy has been observed mainly in Earth’s uppermost and lowermost mantle. Yet, accumulating evidence suggests the presence of significant seismic anisotropy in the transition zone and the uppermost lower mantle. The nature of uppermost mantle seismic anisotropy is relatively well established, and some consensus exists to first order on the large-scale distribution of anisotropy in D". There is, however, little consensus on the character and strength of seismic anisotropy in the mantle transition zone and the uppermost lower mantle. It remains unclear at these depths how seismic anisotropy is related to mantle flow and the deformation mechanisms of mantle minerals. Interpreting seismic observations in the context of mantle dynamics requires input from mineral physicists and geodynamicists; they can relate the seismic velocities and anisotropy to temperature, composition, and deformation of the corresponding materials. Here an interdisciplinary team of seismologists, geodynamicists, and mineral physicists aim to further advance the understanding of the seismic and viscosity structures, and the nature of mantle flow in two regions: 1) the D" layer, in continuation of their previous works; (2) the extended transition zone located at depths ranging from ~400 to 1000 km within the Earth.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.