How to map (survey) the structure of crust
What you have probably seen in the movies, as used by the oil and gas industry is reflection seismology. This is where you shoot off a sound source (explosives, airguns, etc) and track the reflections of the sound waves from the various rock layers below the surface.  

At a smaller scale, there is Ground Penetrating Radar, good for a few 10s of meters at best, which is higher resolution and good for detecting voids.