  The late afterglow of gamma-ray burst is believed to be due to progressive
deceleration of the forward shock wave driven by the gamma-ray burst ejecta
propagating in the interstellar medium. We study the dynamic effect of
interstellar turbulence on shock wave propagation. It is shown that the shock
wave decelerates more quickly than previously assumed without the turbulence.
As an observational consequence, an earlier jet break will appear in the light
curve of the forward shock wave. The scatter of the jet-corrected energy
release for gamma-ray burst, inferred from the jet-break, may be partly due to
the physical uncertainties in the turbulence/shock wave interaction. This
uncertainties also exist in two shell collisions in the well-known internal
shock model proposed for gamma-ray burst prompt emission. The large scatters of
known luminosity relations of gamma-ray burst may be intrinsic and thus
gamma-ray burst is not a good standard candle. We also discuss the other
implications.
