Origin of seismic heterogeneity and attenuation in the Earth's upper mantle and transition zone

地球是一个充满活力的星球，其不断变化的表面部分是由其内部深处的过程形成的，这些过程控制着地震、火山和山脉的形成。地球最上层地幔和过渡带（在地表以下50-660公里深处）的流动驱动着板块构造，这是我们的星球与其他星球区别开来的特征之一。然而，我们对地幔还有很多不了解的地方：地球性质的变化尺度有多大？地幔结构的变化是由温度和/或化学成分引起的吗？地幔向哪个方向流动？地震学、热力学建模和岩石物理学的最新发展有可能帮助解决这些问题。现代高性能计算使我们能够对来自世界各地的大规模免费地震数据集进行有效的分析和建模，使我们能够生成越来越详细的地球内部图像。岩石和矿物物理实验室实验的进展，以及热力学理论的新发展，现在允许建立热力学自洽的行星内部的现实模型。由于这些不同技术的联合使用，过去很难估计的地球特性今天已经触手可及。固有地震衰减（由于内摩擦或非弹性过程引起的地震波传播的振幅损失）特别有趣，当使用地震学、矿物/岩石物理学和地球动力学联合解释时，它对温度、化学成分和地幔中流体的存在提供了独特的见解。然而，到目前为止，地震衰减受到的关注相对较少，对地球内部进行这种综合研究的努力很少，也很有限。这个项目解决了这些问题，目的是大大提高我们对地球内部发生的物理和化学过程的基本理解，特别是在最上层的地幔和过渡带。我们将通过组装一个新的大规模地震数据集来实现这一目标，该数据集将首次以完全一致的方式与新的热力学和岩石物理信息一起建模和使用，以建立新的全球衰减和地震速度的三维图像，并推断地幔的温度，化学成分和流动。这将有助于我们推断出地球性质变化的规模、分布和机制，以及上地幔和过渡带的衰减，从而更好地理解地球深处这一关键组成部分的动力学。我们聚集了一个由三名英国科学家组成的团队，他们在地震学、地球动力学和矿物物理学方面具有互补的专业知识，并得到了国际多学科合作伙伴的支持，他们的技能和知识将为地球内部的三维地震热力学特征建立一个新的框架。我们将以我们最近在新的地震数据分析和成像策略以及矿物学和动力地幔建模方面的工作为基础。在两名博士后助理的帮助下，我们将在这个为期3年的研究项目结束时，对地幔动力学过程有了新的认识，对地球深部综合研究有了新的工具和框架，并将在项目结束后广泛传播。到目前为止，还没有对地球上地幔和过渡带的三维衰减、地震速度、温度、化学成分和流动进行过如此全面、跨学科的研究。

The Earth is a dynamic planet with a changing surface partly shaped by processes in its deep interior, which control earthquakes, volcanoes and the formation of mountain ranges. Flow in the Earth's uppermost mantle and transition zone (at depths of ~50-660 km beneath the surface) drives plate tectonics, one of the features distinguishing our planet from others. However, there is much that we do not know about the Earth's mantle: What are the scales of variation in the properties of the Earth? Is variation in the structure of the mantle due to temperature and/or chemical composition? In what directions does mantle flow? Recent developments in seismology, thermodynamic modelling and rock physics have the potential to help solve these questions. Modern high performance computing is enabling the efficient analysis and modelling of freely-available large-scale sets of seismic data from around the world allowing us to generate increasingly detailed images of the Earth's interior. Progress in rock and mineral physics laboratory experiments, along with new developments in thermodynamic theory, now allow the construction of realistic models of planetary interiors that are thermodynamically self-consistent. As a result of the joint use of these different techniques, properties of the Earth that were very difficult to estimate in the past are within reach today. Intrinsic seismic attenuation (the amplitude loss of propagating seismic waves due to internal friction or anelastic processes) is particularly interesting, giving unique insight about temperature, chemical composition and the presence of fluids in the Earth's mantle when jointly interpreted using seismology, mineral/rock physics and geodynamics. However, up to now, seismic attenuation has received relatively little attention, and efforts for such integrated studies of the Earth's interior have been rare and limited. This project addresses these issues, with the aim of substantially advancing our fundamental understanding of the physical and chemical processes occurring in the Earth's interior, notably in the uppermost mantle and transition zone. We will achieve this by assembling a new massive seismic dataset, which will be modelled and used for the first time along with novel thermodynamical and rock physics information in a fully consistent way, to build new global 3-D images of attenuation and seismic speed in the Earth's mantle, and infer mantle's temperature, chemical composition and flow. This will help us deduce the scale, distribution and mechanisms responsible for variations in Earth's properties and attenuation in the upper mantle and transition zone, leading to an improved understanding of the dynamics of this key component of the deep Earth. We have gathered a team of three UK scientists with complementary expertise in seismology, geodynamics and mineral physics, supported by international multidisciplinary partners, with the skills and knowledge to build a new framework for the 3-D seismo-thermodynamic characterization of the Earth's interior. We will build on our recent work in novel seismic data analysis and imaging strategies, and on mineralogical and dynamical mantle modelling. By the end of this 3-year research project, with help from two postdoctoral assistants, we will have new knowledge about the dynamic processes in the Earth's mantle, and new tools and frameworks for integrated deep Earth research, which will be widely disseminated beyond the project's duration. So far no studies of 3-D attenuation, seismic speed, temperature, chemical composition and flow in the Earth's upper mantle and transition zone have used such a comprehensive, interdisciplinary approach.