A joint hypocenter-velocity inversion for the eastern Tennessee seismic zone (ETSZ) has produced one-dimensional P- and S-wave velocity models for the upper crust. The models, called ET1D, are based upon P- and S-wave arrival times from 492 earthquakes recorded by regional seismic networks. P- and S-wave velocity models were computed independently. The final 1D velocity models display a systematic increase of velocity with depth and a stable Vp/Vs ratio between 1.72 and 1.74. Relocation using ET1D reduced scatter in hypocenter locations, primarily through changes in focal depth. Relocated hypocenters also had reduced RMS residuals, horizontal errors, and vertical errors relative to values obtained with the velocity model presently used for hypocenter determinations in the ETSZ. ET1D was extended to include the entire crust to allow this model to be used for routine hypocenter determinations in the ETSZ.