A seismic velocity profile in a region of interest in a subsurface formation is determined using at least the following steps. (a) Activating a seismic source at a location n, thereby exciting a wave in the subsurface formation. (b) Recording a wave signal trace unm(t) against time t, at a seismic receiver m. (c) Recording a wave signal trace unk(t) against time t at a seismic receiver k. (d) Cross correlating the wave signal traces unm(t) and unk(t) to obtain uconvnmnk(t). (e) Repeating these steps, for different locations n; (f) Summing uconvnmnk(t) over all locations n, to obtain a signal trace uvsmk(t) which corresponds to the signal received by the seismic receiver k from the virtual source at the position of seismic receiver m; (g) Deriving the seismic velocity based on the time of first arrival of the wave in uvsmk(t) and the predetermined distance between the seismic receiver m and the seismic receiver k.