1. A method, comprising the steps of: a) providing seismic data containing information about a subsurface feature in the earth and noise, said subsurface comprising a reservoir, said providing of seismic data comprising: i) a first dataset comprising a first up-going wave-field and a first down-going wave-field (U 1 , D 1 ), ii) a second dataset comprising a second up-going wave-field and a second down-going wave-field (U 2 , D 2 ), wherein the second dataset is collected at a time that is later than the first dataset by a time interval; b) creating an up-going 4D difference dataset U by subtracting one of the first and second up-going wave-fields U 1 , U 2 from the other and creating a down-going 4D difference dataset D by subtracting one of the first and second down-going wave-fields D 1 , D 2 from the other; c) creating a weighting function W that is a function of the similarity of the up-going 4D difference dataset and the down-going 4D difference dataset D; e) generating a 4D similarity stack, where the 4D similarity stack is defined as (U+D)*W/2, wherein 4D noise is suppressed and a desired 4D signal containing information about the subsurface feature is preserved; and f) delineating a change in said reservoir from said 4D signal.