The seismological literature contains an abundance of theory to describe seismic waves in layered media. A significant aspect of applied seismology is the general neglect of intrabed reverberation. When a wave reflects from an interface, the strength of the reflected wave is a small fraction, typically less than 10%, of the strength of the incident wave. This reflected wave is the one that is mainly dealt with in this book. However, the reflected wave itself reflects again and again, ad infinitum. For short path geometries, there can be very many of these rays. The question is whether these reverberations can ever amount to enough to make considering them worthwhile. The answer seems to be that although reverberation may be significant, seismologists are rarely able to improve interpretation of reflection survey data with the more complicated theory that is required to incorporate reverberation.
The situation is somewhat improved when well logs are available, but even then there are serious difficulties. The best possible lateral resolving power, say about 20-50 meters, is obtained after migration. The well log, however, is not a 20-50 meter lateral average of the earth. Next time you see a highway cut through sedimentary rocks, think of the difference between a point and a lateral average over 20-50 meters. In practice, people smooth the well log (vertical smoothing). Too little smoothing gives too much reverberation. Too much smoothing gives no reverberation. The amount of vertical smoothing is an empirically determined parameter, and results are significantly sensitive to it. Vertical averages of the well log may or may not be a satisfactory approximation to the required horizontal average.