Figure 1: (GIF) (PS) CDP gather geometries for two different split-spread shooting strategies. In the lower example, the reciprocity principle has been used to double the number of offsets sampled. The shot and group intervals are the same in both examples.

Figure 2: (GIF) (PS) Eisner's paradox. ``S'' is an isotropic source, and ``R'' is an isotropic receiver. (If you are viewing it in color, note rays emerging from the source are white, while rays reflected once off the truncated ellipse are cyan.) As is obvious from the figure, nearly twice as much energy is recorded at the receiver in case A than there is in case B. Reciprocity demands that the complete seismogram recorded in each case be the same. Does reciprocity hold in this example?

Figure 3: (GIF) (PS) Reciprocity vindicated. The numerical integrals show that the amplitude is indeed exactly the same in both cases, even though the energy differs by a factor of almost 2.

Figure 4: (GIF) (PS) The sophomore paradox, and its resolution. Left: two positive colliding pulses. Right: pulses of opposite sign colliding. Bottom: Energy conservation says that each trace has the same area. The velocity and energy fields were calculated numerically from the corresponding pressure fields by the method stated in the text.