A method and computer instructions on computer readable media for determining and analyzing spatial changes in the earth's subsurface associated with dip vectors measured using 3D data in regions near a fluid contact or seismic flat spot event. The method obtains seismic attribute data, then derives corresponding 3D dip and azimuth as a 3D volume and derives corresponding 3D reliability volumes or 3D censor volumes. A set of vector is formed within a local subvolume of interest interior to the focused subvolume of interest for each reliability location, and a subset of local vectors within a user specified deviation of the azimuth of the structural dip vector are identified. A set of candidate flat spot dip vectors within the local subvolume of interest are identified enabling a significance measure for each vector within the set of candidate flat spot dip vectors to be determined.