Spall, the tensile failure of a material due to high stress loading, has been observed in a number of contained and surface explosions. The phenomenon results in a repartition of the initial spherical explosion energy source, yielding a second energy source which is cylindrical and delayed in time. Recent spall models by Day et al. (1983) demanding conservation of momentum have shown the phenomenon to have little contribution to 20-sec surface waves. These models are extended to include the effect of the process on near-source seismograms. The spall model is constrained by observations within the nonlinear regime of the source which bound the mass, momentum, and timing of the process. Comparison of these forward models with the inverse vertical point force source inferred from seismic recordings of a bermed surface explosion yields excellent agreement. The spall model developed from the contained explosion, CHEAT, is used to create synthetic seismograms. Comparisons of these waveforms with those from a Mueller-Murphy contained explosion indicate that the waveform contribution from spall is similar in size to the spherical explosion waveform. The complete synthetic composed of the spall and explosion contribution compares favorably with observational data from the CHEAT experiment in both amplitude and energy distribution.