First I show that equation (5) and (4) are numerically equivalent and produce identical results, as predicted analytically. Figure illustrates a wave field propagating in the model that shows a step discontinuity but is otherwise homogeneous. The elastic wave propagates across a discontinuity in vp and vs. Figure shows a comparison of two modeling responses. One result was calculated using equation (5) and one result was obtained using equation (4). For comparison I extract a single trace from the recorded wave fields, as shown in Figure . There is no noticeable difference between the two curves for each of the two components. For both components the resulting responses overlie each other perfectly and indicate that both modeling equations are also numerically equivalent.