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3-D variations of wave speeds and density have shown the presence of seismically distinct structures in the Earth's mantle. However, seismology does not directly provide information on the thermochemical properties of these structures, which is crucial for understanding mantle dynamics and thus, planetary evolution and origin. Comparing observed seismic data with mineral properties obtained from mineral physics allows us to make thermochemical interpretations of seismic observations. Inverting seismic properties for thermochemical properties is challenging because of the non-uniqueness of the problem: different combinations of temperature and composition can produce the same seismic properties.