Dr. Raj Moulik, Postdoctoral Researcher at U. Maryland, presents " Signatures of chemical heterogeneity in the lowermost mantle from Full Spectrum Seismic Tomography".

"Is there a chemically distinct reservoir in the Earth?
Do superplumes overly denser-than-average material?
Can we detect these anomalies with seismic data?
Can we evaluate statistical significance of the features in tomography?
This study presents the strongest evidence till date (ca. 2015) of large-scale thermo-chemical heterogeneities in the lowermost mantle using the full spectrum of seismic data. A large data set of surface-wave phase anomalies, body-wave travel times, normal-mode splitting functions and long-period waveforms is used to investigate the scaling between shear velocity, density and compressional velocity in the Earth's mantle (ϱ=dln ρ/dln vS, ν=dln vS/dln vP). Our preferred joint model consists of denser-than-average anomalies (~1% peak-to-peak) at the base of the mantle roughly coincident with the low-velocity superplumes. The relative variation of shear velocity, density and compressional velocity in our study disfavors a purely thermal contribution to heterogeneity in the lowermost mantle, with implications for the long-term stability and evolution of superplumes."