  The modes of decay for the even-even isotopes of superheavy nuclei of Z = 118
and 120 with neutron number $160 \leq N \leq 204$ are investigated in the
framework of the axially deformed relativistic mean field model. The asymmetry
parameter $\eta$ and the relative neutron-proton asymmetry of the surface to
the center ($R_{\eta}$) are estimated from the ground state density
distributions of the nucleus. We analyze the resulting asymmetry parameter
$\eta$ and the relative neutron-proton asymmetry $R_{\eta}$ of the density play
a crucial role in the mode(s) of decay and its half-life. Moreover, the excess
neutron richness on the surface facets a superheavy nucleus for $\beta^-$
decays.
