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

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.

The aim of this project is to produce a step change in our fundamental understanding of the mechanisms responsible for 3D structure in the Earth's upper mantle and transition zone, bringing new insight into the thermal, chemical and dynamic behaviour of the Earth's interior. We will provide high-level training of two PDRAs in geophysics, which is one of the specialisations listed in the UK's home office shortage occupation list. Given the fundamental nature of the project, the main non-academic beneficiaries of this work will be: (i) users working on practical applications requiring a good knowledge of the 3D structure of the Earth's interior, such as from government and non-government seismic monitoring agencies responsible for routine earthquake source characterizations and nuclear explosion monitoring; and, (ii) school children, teachers and the wider public, by motivating young people for exciting science, encouraging them to choose science subjects at school and university and thus contributing to the UK's skillbase.

Our new 3D Earth models will be useful for seismic monitoring efforts, such as for more accurate estimates of earthquake sources and associated ground motions, and nuclear explosion verifications. Although we will focus on the Earth's global scale, the lessons learned will also be useful for regional/local applications. We will use our network of contacts in national and international seismic monitoring agencies (e.g., Los Alamos Nat. Lab., USGS, BGS) to disseminate our project, facilitated by the fact that the project's lead PI (A. Ferreira) works on both Earth structure and earthquake source imaging. Dr H. Patton (Los Alamos Nat. Lab.), who has a lifetime experience in earthquake and nuclear explosion monitoring, will serve the project as international impact adviser (see letter of support), advising the project from the outset and participating in the project's 2-day workshop, which will involve members of the seismic monitoring community (e.g., from CTBTO, USGS, BGS). The conclusions of the workshop will be published in a media-friendly journal (e.g., Eos, Astronomy & Geophysics) accessible to members of seismic monitoring agencies. We will use our strong links with major European and international programmes (e.g., QUEST, CIG, IRIS) to distribute our project's outputs. All these programmes are highly-visible and accessed by both academics and non-academics, including members of the seismic monitoring community.

We shall build on ongoing engagement activities by the project PIs/co-Is, such as seismometer demonstrations in schools, participation in teaching training events, local and national exhibits, and leverage activities with the geophysics industry, following a more structured approach. We will build on our existing links with the Teacher Scientist Network (www.tsn.org.uk, see support letter) to work with focus groups of teachers and students. Together, we will create new 3D deep Earth visualisation teaching and engagement materials, which will help strengthening geosciences in school curricula and engage students in the scientific process. If funded, the project will be introduced at a GIFT workshop (Geoscience Information For Teachers) in the 2013 EGU meeting, to ensure its wide-user visibility and feedback from the outset. We will also apply for project exhibits using the new 3-D visualisation materials in venues such as the Royal Norfolk Show and the Royal Society's Summer Science Exhibition. The PIs/co-I and PDRAs will prepare a popular science article for publication, e.g., in New Scientist or NERC's Planet Earth magazine. Moreover, we will communicate our findings to the media, by using UEA and UCL's press office services and training courses, and will facilitate a comprehensive training of the PDRAs, including knowledge-exchange skills, attending media training courses, co-organising the project's workshop and developing effective skills in science communication to the wider public.