  Very-high-energy (VHE) photons around TeV energies from a gamma-ray burst
(GRB) jet will play an essential role in the multi-messenger era, with a fair
fraction of the events being observed off-axis to the jet. We show that
different energy photons (MeV and TeV photons in particular) arrive from
different emission zones for off-axis observers even if the emission radius is
the same. The location of the emission region depends on the jet structure of
the surface brightness, and the structures are generally different at different
energies, mainly due to the attenuation of VHE photons by electron-positron
pair creation. This off-axis zone-shift effect does not justify the usual
one-zone approximation and also produces a time-delay of VHE photons comparable
to the GRB duration, which is crucial for future VHE observations, such as by
the Cherenkov Telescope Array.
