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E321: Seismic signatures of deep stagnating slabs (Lead Supervisor: Sanne Cottaar, Earth Sciences)

Supervisors: Sanne Cottaar (Earth Sciences) and Arwen Deuss (University of Utrecht)

Importance of the area of research:

Recently, high resolution seismic tomography (Fukao & Obayashi, 2013) has found that slabs in the deep mantle show a range of different behaviours:  Some subducting slabs stagnate at the bottom of the mantle transition zone (at 660 km) and some between 700 and 1000 km, while others continue towards the core-mantle boundary. Complimentary to seismic tomography, one can study the topography and amplitudes of seismic discontinuities. Seismic discontinuities are related to mineral phase transitions; their topography and amplitudes provide - combined with information from mineral physics - constraints on the phases present and the temperatures at these depths. The signatures of the discontinuities in various slabs will lead to further constraints on why the slabs behave differently.

Project summary:

The goal of this project is to characterize seismic discontinuities between 400-1000 km depth in regions with various types of subducting slab behaviours. The mapping will be done using P phases that convert at the seismic discontinuities to S phases (P-to-s conversions). The student will look for anomalous signatures within the slab and at the depths where it might be stagnating.  The results will be interpreted by creating synthetic data with the latest results in mineral physics. This project is a continuation of the work of Cottaar & Deuss (2015) on ponding slabs beneath Europe.

What the student will do:

The student will choose a region with interesting slab behaviour and suitable seismic data coverage, e.g. South and Central America or Japan.  Seismic data will be downloaded and processed and P-to-s conversions will be studied by computing and stacking so-called receiver functions.  Separately the student will apply results from mineral physics to create synthetic data to interpret the signatures seen in the real data.  The student is free to extend the project by comparing more regions or by analysing complimentary data sets, e.g. reflections from the bottom of the seismic discontinuities.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Cottaar, Sanne, and Arwen Deuss.(2016) Large‐scale mantle discontinuity topography beneath Europe: Signature of akimotoite in subducting slabs."Journal of Geophysical Research: Solid Earth 121.1 : 279-292.

Fukao, Y., and M. Obayashi (2013), Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity, J. Geophys. Res. Solid Earth, 118, 5920–5938, doi:10.1002/2013JB010466.

King, Scott D., Daniel J. Frost, and David C. Rubie (2015) Why cold slabs stagnate in the transition zone. Geology 43.3: 231-234.

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