Effects of rock damage on teleseismic mb are investigated with P wave synthetic seismograms using a moment dipole Mzz as the equivalent elastic model for damage around buried explosions. Two manifestations of late-time damage, cavity rebound and bulking from block rotations, are represented by model decompositions into compensated linear vector dipole and monopole sources, respectively. For high-velocity media, P waves from damage destructively interfere with those from the explosion. This interference reduces the rate at which mb yield scales for a pure monopole source and provides a physical basis for observed scaling in hard rock, mb ~ 0.75 log[yield]. For over-buried explosions, such as the North Korean tests, P waves from damage are weaker, and higher scaling rates are expected than explosions conducted under standard containment conditions. Our results highlight a cautionary note of transporting the same mb-log[yield] relation between test sites to estimate yield when source phenomenology is likely to be very different.