Abstract: A method of analysing a subsurface region. 4D seismic data is received from a subterranean reservoir that is being seismically evaluated. A first set of values representing a first attribute at a plurality of first coordinates within the subsurface region is obtained from the 4D seismic data. A second set of values representing a second attribute at a plurality of second coordinates within the subsurface region is also obtained from the 4D seismic data, wherein each of the plurality of second coordinates corresponds to a respective first coordinate. For each first coordinate, a measure of dependence is calculated and the calculated measure of dependence is used to detect changes in the reservoir over time.