Professor Barbara Romanowicz
In the last two decades, seismic tomography has generated spectacular images of 3D structure in the earth's interior, providing insights on mantle flow and the dynamic processes that drive plate tectonics. I will first discuss some key unresolved issues in global dynamics of the earth's interior, and review the current status of global mantle tomography, contrasting images obtained using different datasets and inversion methodologies, and discussing their various strengths and limitations. I will point out how features associated with the downgoing convective flow appear better understood at the present time than those associated with upwellings. I will then describe how new waveform inversion approaches can lead to significant progress in seismic imaging of "hotter" regions, and discuss the much debated issue of "mantle plumes". I will discuss evidence which shows that heterogeneity in the deep mantle cannot be purely thermal, but must involve strong lateral variations in composition. I will conclude by identifying promising new approaches, both in data gathering and theory, that aim at imaging the scattered wavefield and obtain higher resolution constraints on mantle heterogeneity.