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

地球是一个动态的行星，它的表面不断变化，部分是由其内部控制地震、火山和山脉形成的过程塑造的。地球最上面的地幔和过渡带(在地表下约50-660公里处)的流动驱动着板块构造，这是我们的星球区别于其他星球的特征之一。然而，关于地幔，我们还有很多不知道的东西：地球性质的变化有多大？地幔结构的变化是否由于温度和/或化学成分的影响？地幔向什么方向流动？地震学、热力学模型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可免费获得的大规模地震数据集进行有效的分析和建模，从而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步，以及热力学理论的新发展，现在可以建造热力学上自洽的行星内部的现实模型。由于联合使用这些不同的技术，过去很难估计的地球特性今天变得触手可及。本征地震衰减(由于内耗或滞弹性过程引起的传播地震波的幅度损失)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，它提供了关于地幔中温度、化学成分和流体存在的独特见解。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也是罕见的和有限的。这个项目解决了这些问题，目的是大大促进我们对地球内部发生的物理和化学过程的基本了解，特别是在最上面的地幔和过渡带。我们将通过汇编一个新的大规模地震数据集来实现这一点，该数据集将首次与新的热力学和岩石物理信息一起进行建模和使用，以建立新的全球地幔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导致地球性质变化和上地幔和过渡带衰减的规模、分布和机制，从而更好地了解地球深部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方面具有互补的专业知识，在国际多学科合作伙伴的支持下，拥有技能和知识，为地球内部的三维地震热力学表征建立了一个新的框架。我们将在新的地震数据分析和成像策略以及矿物学和动力学地幔模拟方面的最新工作基础上再接再厉。到这个为期3年的研究项目结束时，在两名博士后助理的帮助下，我们将有关于地幔动态过程的新知识，以及用于综合深部地球研究的新工具和框架，这些工具和框架将在项目持续时间后广泛传播。到目前为止，还没有关于地球上地幔和过渡带的三维衰减、地震速度、温度、化学成分和流动的研究使用这种综合的、跨学科的方法。

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.