Significant changes in physical properties produce conversions between compressional (P) and shear (S) waves. The Earth’s surface also returns energy to depth that can be reflected back to the surface. Analysis of this chain of conversions and reverberations yields information about the structure beneath the station.
This is a companion discussion topic for the original entry at https://www.geo-down-under.org.au/imaging-the-lithosphere-with-earthquake-sources/