(n.) Geophysics. Three-dimensional (3D) seismic data acquired at different times over the same area to assess changes in a producing hydrocarbon reservoir with time. Changes may be observed in fluid location and saturation, pressure and temperature. 4D seismic data is one of several forms of time-lapseseismic data. Such data can be acquired on the surface or in a borehole. See: Acquisition, Time-Lapse Seismic Data