The background values and the geometry of the reservoir model are plotted in Figure . The reservoir is 50 m thick and the top of the reservoir is at 2 km depth. We simulate water injection wells located at 2 km and 3 km respectively. Table 1 lists the pre-flood and post-flood petrophysical properties at an injection well. The background properties both above and below the reservoir are: Vp = 2.38 km/s, Vs = 1.13 km/s, and = 2.1 g/cc. The relative P impedance contrast is calculated as:
and similarly for the relative S impedance contrast:
where ``+'' superscripted properties refer to the layer below the interface, and ``-'' superscripted properties refer to the layer above the interface. We note that and are exactly twice the normal incidence P and S plane-wave reflection coefficients Rp and Rs:
Figure shows the depth-dependent form of the background model and the reservoir properties at an injection well, pre- and post-flood. Vs is the left-most curve, in the center, and Vp to the right of each panel.