We compute the time integrated , thermal emission produced by a series of radiation mediated shocks that emerge from the photosphere of a GRB outflow .
We show that for a sufficiently broad distribution of shock strengths , the overall shape of the time integrated spectral energy distribution below the peak is a power law , \nu E _ { \nu } \propto \nu ^ { \alpha } , with a slope 1 < \alpha < 2 .
A substructure in the SED can also be produced in this model for certain choices of the shock train distribution .
In particular , we demonstrate that our model can reproduce the double-peak SED observed in some bursts , in events whereby a strong shock is followed by a sequence sufficiently weaker ones .