Fan Shooting
This seismic method allows for determining the thickness of an alluvium, for example, in a ravine. An explosive is used as the source, which must be placed on solid rock at a distance such that the wavefront reaches the geophones as a flat wave. In this way, the arrival time of the wavefront at the geophone placed on solid rock will be shorter than the time recorded by the geophones placed in the alluvium. By knowing these two times and the velocity of the wave through the alluvium, the depth of the alluvium from each geophone to the solid rock can be determined.