In seismology, people use waves generated by earthquakes, artificial explosions, or even "noises", to detect the Earth's interior structure. The waves traveling in rocks, which are the main components of Earth's crust and mantle, are elastic waves. A key problem in seismology is whether the interior structures of interest could be uniquely determined by the measurements people can collect. Since in most situations, people can only record the vibrations at the surface, such problems usually are formulated as inverse boundary value problems for the elastic wave equation. We study several inverse boundary value problems for the elastic wave equation and give some uniqueness and stability results for them.