Using numerical simulations, we study the evolution of silicon in the passage of a constant-pressure shock wave launched from an adjacent pusher. We examine also its optical characteristics of reflectivity and emission. Our finding points to the study of shocked interfaces as a novel means to explore nonequilibrium, non-steady-state behaviors of shock states and an alternative approach to assess electron-ion equilibration rate in a shock wave. It also reveals important structures in such a shock wave in contrast to its usual notion as a propagating discontinuity. This offers some possibilities for reconciling the different findings on the compressibility of deuterium.