With seismic tomography, scientists map out large regions where seismic waves travel slower or faster than average to develop images of individual slices through Earth's interior. Seismic waves travel faster through cold, stiff materials, like a subducting plate, and slower through warmer materials, like hot rock rising to the surface. These models—with areas where seismic waves travel more quickly in blue, and slower areas in red—allow scientists to infer structures like sinking tectonic plates