[seismology] Slowness (s) is a quantity introduced in Seismology which is the reciprocal of velocity. Thus travel time of a wave is the distance that the wave travels times the slowness of the medium ( in seismology, it refers to different layers of Earth exhibiting different densities) Thus, Slowness = 1/Velocity Therefore, the residual tr... Found on http://en.wikipedia.org/wiki/Slowness_(seismology)