In seismic investigations, a method of velocity analysis associated with the normal moveout correction (ΔT), which enables the root-mean-square velocity (vrms) to be calculated down to a particular reflector for which the normal incidence two-way travel time (t0) and ΔT are known for a given offset (x) such that vrms = x/(2t0ΔT)1/2. Once vrms is known, the depth (z) to the reflector can be calculated using z = vrmst0/2.