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

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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.