Regional arrays of seismometers provide a powerful means of mapping the details of deep-Earth structure. Our understanding of the geological processes at work within our planet depends on our ability to examine them; seismic techniques remain the best tool available. However, spatial aliasing due to the less-than-optimal distribution of global seismometers has long made it difficult to determine deep-Earth structure from teleseismic waves. The temporary deployment of portable broadband seismometers can help by providing high-resolution windows into the Earth. Patterns of global mantle convection create seismically observable features such as anisotropy at the top and bottom of the mantle, topography of upper mantle discontinuities, and heterogeneous structure at the core-mantle boundary.