The problem of defining design parameters for structures capable of withstanding blast-induced ground shock suggested the use of shock spectra as a suitable means of presenting environmental conditions. Self-contained mechanical reed gages, capable of measuring the displacement shock spectrum over a frequency range of 3 to 300 cps in any one direction, were placed on Shots Stokes, Smoky, Galileo, Whitney, and Charleston. Canisters containing the gages were normally placed with tops flush to the ground level at predicted pressure levels of approximately 100 psi; however, on Shot Smoky two additional gages were placed on the floor of an earth-covered-personnel shelter, and two gages were installed on a concrete block for Shot Whitney. A composite plot of the results of surface gages from Shots Smoky, Galileo, and Whitney indicates some definite trends. The displacements are 2 to 3 times higher at 3 cps for the vertical component than for the radial component. The rate of decrease of displacement with increasing frequency is greater for the vertical component than for the radial component. A comparison of the results from the surface gages and those within the structure on Shot Smoky indicates an attenuation factor of three for vertical displacements, with no appreciable change in the radial direction.