In the application of either ray theory or approximate wave methods, a rational decision must be made as to the phases which contribute significantly to ground motion. In multilayered media, many phases travel by different paths but arrive with the same travel time (kinematic analogs). Some of these have the same amplitude and phase characteristics (dynamic analogs), and the number of phases in each dynamic analog must be determined. Given the number of layers and the maximum number of path elements, equations are given to yield the desired quantities. With the use of amplitude distance curves, it is possible to determine which phases in refracted, reflected, or head waves make significant contributions to a synthetic seismogram.