Abstract: A method, computer program product and system for improving the accuracy and detail in determining changes in properties associated with sub-surface geological structures. A first and a second time-lapse seismic data taken for a first and a second seismic survey, respectively, are received. If no calibration for the first and second time-lapse seismic data are needed, then an absolute time-lapse comparison is made. In the absolute time-lapse comparison, the time-lapse seismic data taken at a depth level below a reference level is compared with time-lapse seismic data taken at the reference level. If however, calibration is needed, then a residual time-lapse comparison is made. In the residual time-lapse comparison, the derived residual phase and amplitude differences at a depth level below the reference level are compared with the derived residual phase and amplitude differences at the reference level.