Phase Transformations, Microstructures, and their Seismic Signals from the Earth's mantle

我们对固体地球的知识建立在不同领域的一致研究基础上：例如，矿物中的相变在地球内部引起物理边界。对这些区域产生的地震信号的分析为我们了解地球的结构、组成和动力学提供了关键信息。由于地球内部极端的压力和温度条件，矿物发生了剧烈的变化，必须在现实条件下在实验室中研究它们的性质。同时，地震学是直接观测地球深层结构的为数不多的手段之一，因为地震波形受到沿其传播路径的物质的现代状态的限制。例如，通过地震学研究了在660公里深处向下地幔的转变。矿物物理证明，这主要是由于矿物环木石分解成铁方镁石和水镁石。我们能否使我们的地球模型超越地震间断和矿物反应深度之间的简单比较？我们能用来自边界层的地震信号来描述地球深处的过程吗？这会改变我们目前对地球的看法吗？这些都是永恒计划致力于回答的问题。相变不仅会引起材料的结构、密度、弹性性质的变化，还会引起微观结构的变化，即矿物相的排列、颗粒尺寸、颗粒取向和应变。地球上具有不连续物理性质的边界会在地震信号中产生特征。但在地震学中测量到的部分信号及其与地球深部过程的联系还没有完全被理解。尤其是位于600-1700公里深度的地区，在660公里处有复杂的反射结构，在中地幔深度有小尺度结构，在~1000公里处有难以捉摸的补充不连续。到这个项目结束时，我们打算约束和模拟相变和微结构对这种观测的影响，并使用这一新知识来解释这个深度范围内的物理过程。该项目需要高压/高温实验研究和最先进的原位方法，以了解相关矿物成分中的相变诱导的微观结构。同时，我们将进行地震学研究，以分析新的波组合，当这些波组合在一起使用时，将提供更强的可能性来破译地幔结构的物理参数。将这两个场结合起来，可以更好地理解相变、微结构及其相关地震信号之间的联系。永恒号的目标是开发新的方法，解决不能通过简单分析热力学相变序列来解释的问题，因为它们涉及地球深处的微结构和动态过程。

Our knowledge of the solid Earth is built upon concerted research in different fields: For example, phase transformations in minerals induce physical boundaries in the Earth's interior. The analysis of seismic signals arising from these regions brings key information for our knowledge of the structure, composition, and dynamics of the planet. Due to the extreme conditions of pressure and temperature in Earth's interior, minerals undergo drastic transformations and their properties must be investigated in laboratories under realistic conditions. In parallel, seismology is one of the few means of direct observation of deep Earth structures as seismic waveforms are constrained by the present-day state of matter along their propagation path. The transition into the lower mantle at 660 km depth, for instance, has been characterized through seismology. Mineral physics demonstrated that it is mostly due to the decomposition of the mineral, ringwoodite, into ferropericlase and bridgmanite. Can we move our Earth model beyond simple comparison between seismic discontinuities and mineral reaction depths? Can we use seismic signals from boundary layers to characterize processes deep inside the Earth? Will this change our current view of the Earth? These are the questions the TIMEleSS project aims to answer. Phase transformations induce changes in the material's structure, density, elastic properties, but also microstructure, i.e. the arrangement of mineral phases, grain sizes, grain orientations, and strains. Boundaries with discontinuous physical properties in the Earth induce signatures in the seismic signals. But part of the signals measured in seismology and their connection to deep Earth processes are not fully understood. This is especially true for the regions lying between 600 and 1700 km depth, with a complex structure of reflections at 660 km, small scale-structures at mid-mantle depth, and an elusive supplementary discontinuity at ~1000 km. By the end of this project, we intend to constrain and model the effect of phase transformations and microstructures on such observations and use this new knowledge to interpret physical processes in this depth range. This project requires high pressure/temperature experimental studies and state-of-the art in-situ methods for understanding microstructures induced by phase transformations in relevant mineral compositions. In parallel, we will conduct seismological studies to analyze new combinations of waves, that, when used together, offer stronger possibilities to decipher physical parameters of structures in the mantle. Combining these two fields allows to better understand connections between phase transformation, microstructures and their associated seismic signals. TIMEleSS' goal is to develop new approaches and to address questions which cannot be explained by a simple analysis of the sequence of thermodynamic phase transitions as they involve microstructural and dynamic processes deep inside the Earth.