Seismics base on measuring travel times of seismic waves, that propagate through subsurface with material specific velocities. The seismic waves are excited by seismic sources as hammer, accelerated weight drop or explosives.
Investigation depth: 10 meter up to 1000s of meters
Reflection seismics base on the velocity measurement of elastic waves that are reflected at layer boundaries.
Investigation depth: ca. 10 m bis 1000 m
Refraction seismics use the refracted energy of artifically excited seismic waves (see also Seismics). For this purpose travel times of head waves, i. e. seismic waves are evaluated that were refracted at layer bounderies in the subsurface.
Investigation depth: up to 50 m (even deeper for research purposes)