  Tidal streams and stellar shells are naturally formed in galaxy interactions
and mergers. The Giant Stellar Stream (GSS), the North-East (NE), and Western
(W) stellar shelves observed in Andromeda galaxy (M31) are examples of these
structures and were formed through the merger of M31 and a satellite galaxy.
Recent observational papers have provided strong evidence that the shells and
GSS originate from a single progenitor. In this paper, we investigate the
formation of these two stellar shelves and the detailed nature of their
relationship to the GSS. We present numerical simulations of tidal disruption
of a satellite galaxy assuming that it is a progenitor of the GSS and the shell
system. We represent the progenitor as a dwarf spheroidal galaxy with the
stellar mass of $10^{9} M_{\odot}$ and evolve its merger with M31 for 3 Gyrs to
reproduce the chemodynamical properties of the NE and W shelves. We find that
an initial metallicity of the progenitor with a negative radial gradient of
$\Delta$ FeH = -0.3 $\pm$ 0.2, successfully reproduces observed metallicities
of the NE, W shelves, and the GSS, showing that all these structures can
originate from the same merger event.
