It has become common practice, when considering a plane parallel structure for seismic modelling purposes, to treat the primary PS V and PP reflected arrivals in a similar fashion. For many of the aspects of these investigations the two arrivals may be studied using the same procedures. However, a major area of difference, more crucial in a model with a large number of layers, is the dynamics or amplitude properties of the PS V arrival. In a many layered medium there is only one ray in the PP case, having two P ray segments in each layer for a given source-receiver offset. In the P SV case there is the so called primary ray composed of P ray segments down to the reflector and S V ray segments up to the receiver. This arrival has only one conversion, the reflected conversion at the deepest interface. In addition, there are a number of other multiplied converted waves, each with one P and one S V ray segment per layer, which have identical kinematic properties (travel times) as the primary P SV arrival and may also have different conversion points on the reflecting interface. Due to the increase in the number of conversions in these other rays their amplitudes will be substantially less than that of the primary. However, as the number of layers increases, the number of these extra rays increases significantly. This effect is what will be considered here.
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