We seek to understand the current state, dynamics and dominant processes of the solid Earth. Fundamental questions persist about several planetary-scale geological phenomena:

• What is the nature of mantle convection and what role does the mantle transition zone play in modulating exchange of material between the upper and lower mantle?
• Can we detect and characterize any chemically distinct reservoir in the mantle using seismic data?
• What is the nature of core-mantle interactions and do they result in chemical stratification in the outer core?

Answering such questions requires progress in imaging seismically retrievable parameters (velocity, anisotropy, attenuation and density) and in descriptions that relate them to dynamically relevant properties of the Earth (e.g. composition, temperature, grain size, fabric). We are in the middle of a revolution in seismology due to the improved coverage of high-quality seismic stations and our ability to analyze the data collected using theoretical and computational advancements. For the first time, we have in place techniques that constrain jointly a plethora of complementary seismological observations in an accurate and self-consistent fashion.