Accurate determination of parameters about seismic discontinuities in the earth, such as their depth, existence, and strength, provides critical information about the physical and chemical states and dynamics of the earth's interior. Unfortunately, those parameters can be strongly affected by factors that are not related to the discontinuities. We use synthetic seismograms to estimate the influence of one of those factors, inelasticity, on the apparent depth and detectability of the 410- and 660- kilometer discontinuities obtained from stacking P-to-S converted phases (PdS). Our results show that when PdS travels through a zone with lower-than-normal Q values, the observed depth of discontinuities could be tens of kilometers deeper than the real value, and the stacking amplitudes and consequently the detectability and apparent strength are greatly reduced. This study demonstrates the importance of taking Q structure into account when seismologically detected discontinuity parameters are interpreted.