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Fig. 1: Bulk and shear moduli obtained using the ‘global fit’ (grey squares, solid curves) in comparison to the results of fitting every pressure point individually (red diamonds).
Fig. 2: Elastic constants derived at 40.4 GPa by fitting the synthetic data.
Fig. 3: Uncertainty analysis for the ‘global fit’.


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Authors and Affiliations



A.K., H.M., D.J.F. and T.B.B. discussed the content. A.K. performed the robustness test. H.M. wrote the paper draft. All authors commented on the manuscript.

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Correspondence to H. Marquardt.

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Extended data figures and tables

Extended Data Fig. 1 Raw data collected on single-crystal bridgmanite at two selected pressures and fits from our Letter.

The solid curves are fits to the grey data using the best-fit global model (the ‘global fit’ of ref. 1) and the red dashed curves are individual fits. a, c, Platelet 1. b, d, Platelet 2. a, b, Data collected at 11.8 GPa; c, d, data collected at 31.9 GPa. We note that the orientation of the crystals changed slightly during pressure increase, but was measured at every pressure in our experiment. A ‘tilt’ correction was employed for crystal platelet 1, as mentioned in our Letter1. The procedure is further explained in the Supplementary Information (containing the raw data).

Extended Data Fig. 2 Illustration of how the synthetic dataset at 40.4 GPa was generated using the elastic constants reported in our Letter.

For every pressure point and platelet, velocities in 18 propagation directions were calculated over an angular range of 360° to simulate in-plane rotations between individual measurements that are representative of our low pressure measurements where no overlap of peaks occurred (solid symbols). We randomly changed the velocity values by up to 0.5% to simulate errors typical for single velocity measurements by Brillouin spectroscopy in the diamond anvil cell13. a, Illustration of a complete velocity dataset, using crystal platelet 1 as an example. b, Illustration of a reduced dataset, using crystal platelet 2 as an example. This assumes limited data availability owing to peak overlap or elasto-optic coupling. The example in b corresponds to a situation where 20 directions have been measured in total (10 on each crystal). Solid and dotted curves are results from the ‘global fit’.

Supplementary information

Supplementary Information

This file contains a statement about the raw data presented in the Excel data file

Supplementary Data

This file contains the raw data as they were collected.

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Kurnosov, A., Marquardt, H., Frost, D.J. et al. Kurnosov et al. reply. Nature 564, E27–E31 (2018).

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