The invention is a method of calculating seismic time shifts Δ{right arrow over (t)}(t), comprising: conducting a number (n) of three or more seismic surveys with large time differences such as months or years, producing a number (n) of three or more vintages of seismic data d1(t), d2(t), . . . , dn(t)={right arrow over (d)}(t), each said vintage of seismic data di(t) comprising one or more seismic traces, calculating partial time derivatives from one or more base trace ∂ ∂ t ⁢ d b ⁡ ( t ) multiplied by the sought time shift Δt(t) and setting the product like ∂ ∂ t ⁢ d b ⁡ ( t ) ⁢ Δ ⁢ ⁢ t ⁡ ( t ) = Δ ⁢ ⁢ d , simplified to LΔt(t)=Δd wherein L comprises the partial time derivatives, and forming a set of (n−1) equations {tilde over (L)}Δ{right arrow over (t)}=Δ{right arrow over (d)} which is overdetermined in the series of consecutive time shifts Δ{right arrow over (t)}(t), and solving for the consecutive time shifts Δ{right arrow over (t)}(t).