A parametric investigation of the late stage equivalence of near-surface explosions has been performed using numerical and analytical means. The explosive sources included both nuclear and chemical energy density levels modeled as pancake-shaped masses of wet tuff ground material containing purely internal or downward-directed kinetic energy. All of the analyzed internal energy sources have been shown to be members of one of the late stage equivalent families given approximately by the relationship EsVs0.233=const, where Es is the total source energy and Vs is the total source volume. Using analytic means, a hypothesized, nondimensional expression relating the far field hydrodynamic shock pressure to source parameters, shock position, and shock time of arrival was derived. Recasting the calculated results into the indicated form yields a single, late time, nondimensional shock pressure-distance curve for all of the nuclear energy density level sources (both internal and downward-directed kinetic) analyzed.