Figure 1. A stratigraphic condition illustrating why a synthetic seismogram response may not look like surface-recorded seismic data. The width of the sand body is approximately the same as the dominant wavelength λ of the illuminating seismic wavefield, thus the sand body is a point diffractor, not a reflector, and no seismic reflection event is present. Because log data acquired in the well measure rock properties extending only a meter or so from the wellbore, a synthetic seismogram calculated from these logs will indicate impedance changes at interfaces A and B at the top and base of the sand and show bold reflection events from these two interfaces.