Differential travel times determined by waveform correlation techniques between seismic phase pairs suffer an inherent systematic bias with respect to conventional visual timing methods if the phase pairs have different attenuation histories. Synthetic shear waves are generated with attenuation histories appropriate for multiple ScS waves. The bias between the ScS2-ScS differential time determined by visual onset and a differential time picked by waveform cross-correlation ranges between 2.2 and 3.8 seconds late, for an assumed average Q&bgr; of the mantle of 312 and 156, respectively. Corrections are calculated for the various ScSn-ScSn-1 phase pairs for a range of ScS t* values.