The crosshole seismic tomography is used to detect important heterogeneities and mechanical proprieties of the formations between two boreholes.
The seismic source is inside the borehole "a sparker" and the receivers "24 hydrophones" are in an adjacent one, the sparker is lowered into the borehole one step at the time.
After the processing of the first arrivals of the P waves we obtain a crosssection of the seismic velocities in between the two wellbores.