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 used during Shots Cactus and Koa. Canisters containing the gages were normally placed with their tops flush to the ground level at predicted pressure levels from 75 to 200 psi on both shots. Additional gages were installed in earth-confined arch structures of Project 3.2. Satisfactory records were obtained for both shots. Limited comparisons have been made between the results obtained for the low-yield (Cactus) and high-yield (Koa) shots at the Eniwetok Proving Ground (EPG) and between the results for Shot Cactus and the lowyield Shots Whitney, Galileo, and Smoky during Operation Plumbbob at the Nevada Test Site (NTS). In general, vertical and radial displacements for Shot Koa were much lower than expected from the extrapolation of data obtained from low-yield shots during Operation Plumbbob. Differences in soil conditions, surface versus raised bursts, and topography variations may have been contributing factors. The Appendix contains the preliminary results of intensive parametric analyses and theoretical studies being made in an attempt to establish suitable scaling laws. (Author).