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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Sergei Lebedev, Earth Sciences

Co-Supervisor: Nick Rawlinson, Earth Sciences

Brief summary: 
A new global dataset of seismic surface wave overtones will be used, together with ESA's new satellite gravity data, to map temperature and composition deep within the Earth.
Importance of the area of research concerned: 
Dynamic processes in the Earth’s lithosphere and underlying asthenosphere continue to reshape the Earth’s surface and give rise to mountain building, earthquakes and volcanoes. Terrestrial seismic and satellite gravity data have complementary sensitivity to the deep Earth structure and dynamics. Combining them effectively is an important outstanding challenge that requires accurate joint inversions of measurements for suitably defined observables. Seismic surface waves are widely used to resolve the structure of the upper 300 km of the mantle, but their sensitivity decreases at greater depths. Surface-wave overtones sample a much greater depth range, but they have been more difficult to measure. A new dataset assembled in the supervisor’s group contains measurements for at least 8-10 overtones, presenting an opportunity for inversions for deep Earth structure. In collaboration with the European Space Agency and partners in Europe, the seismic data will be inverted jointly with satellite gravity data, using state of the art computational petrology methods. An important methodological advance, this also promises discoveries on the structure and dynamics of the Earth.
Project summary : 
The first goal of this project is to advance the methods for the seismic and petrological inversions of the surface-wave overtone data. The methods for the inversion of the fundamental mode surface wave data already exist and will serve as a basis. Inversions of measurements for as many as 8-10 overtones are unchartered territory but are now possible thanks to the recent measurements for these overtones. The inversions are expected to resolve the Earth’s structure down to about 1000 km depth and can help combine the seismic and satellite gravity data. The second main goal of the project is to get the most information from both types of data, resolving temperature, composition, density and other properties of the Earth’s mantle.
What will the student do?: 
The student will have at their disposal a very large dataset of millions of measurements. One approach to using the data will be computing global phase-velocity maps for different modes and different frequencies. From these, phase-velocity curves for the overtones can be determined at every point, to be inverted for the deep structure at this point. Another approach will be to compute inter-station measurements of phase velocities. The student will develop and tune existing inversion methods, for the use with many overtones. Petrological inversion will be advanced together with international collaborators and in a planned collaboration with the European Space Agency.
References - references should provide further reading about the project: 
Fullea, J., S. Lebedev, Z. Martinec, N. L. Celli, 2021. WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical-petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data. Geophys. J. Int., 226, 146-191,
Celli, N.L., S. Lebedev, A.J. Schaeffer, C. Gaina, 2020. African cratonic lithosphere carved by mantle plumes. Nature Communications, 11, 92, doi:10.1038/s41467-019-13871-2.
Lebedev, S., A. J. Schaeffer, J. Fullea, V. Pease, 2018. Seismic tomography of the Arctic region: Inferences for the thermal structure and evolution of the lithosphere. In Pease, V. & Coakley, B. (eds.) Circum-Arctic Lithosphere Evolution. Geological Society, London, Special Publications, 460, 419-440,
You can find out about applying for this project on the Department of Earth Sciences page.
Sergei Lebedev
Prof Nicholas Rawlinson
Department of Earth Sciences Graduate Administrator