For the part of our planet that is beyond direct sampling (which is most of it) seismic waves offer an insight into the present day state of the interior. They can illuminate shapes of objects at depths, reveal changes in the state of the material, and offer clues about its texture.  In my research I use observations of seismic waves to probe the interior structure of the Earth. My studies yield information about the speed of different seismic waves: how it changes with depth, and from place to place; whether these changes are smooth or abrupt; whether there is any dependence on the direction in which seismic waves travel. While the means of my research have to do with elastic wave propagation and time series analysis, the motivation and goals are those of geological history and present-day tectonic activity. On the basis of inferences about seismic wave speed inside the Earth I try to understand what is happening there now, or has happened in the past.