This investigation type takes advantage of the possibility to place seismic sensors inside boreholes to get more precise seismic velocity measurements in investigated areas.

Down-hole surveys use a single borehole; a tri-dimensional geophone is anchored to the wall at different depths. Seismic energy is produced at the surface near the hole. By measuring on seismograms the traveltimes it is possible to make a precise estimation of Vp e Vs and, starting from these values, calculate the elastic parameters associated to layers crossed by the borehole.

Two or three boreholes are instead used for cross-hole surveys; they are generally placed just a few meters one to the other. One hole is utilized for seismic energy production (micro-charges, blank cartridges); the other(s) are instead set for seismic recording.
The possibility to make measurements where source and receiver are placed in proximity one to the other allows us to precisely determine Vp e Vs and relevant elastic parameters.

These types of investigations are generally adopted in landslide areas and also for infrastructure planning.