Effects of Repository Depth on Ground Motion: The Pahute Mesa Data

摘要

Measurements of ground motion from ten Pahute Mesa weapons tests were made at seven locations on the Nevada Test Site. Each location had measurements at the surface and at a depth ranging from 61m to 762m, permitting an assessment of the effect of depth on ground motion. Measurements of vertical, radial and tangential acceleration were made at each location and depth, and the three components of acceleration were used to determine peak vector magnitudes of acceleration, velocity, and displacement. Top-to-bottom ratios of the peak vectors were plotted against depth and an exponential least squares fit made to the curve. Ratios of the largest single peaks, averages of the 5, 10, 15, 20, and 25 largest peaks, and ratios of Pseudo Relative Response Velocity (PSRV) were examined. Fits for the multiple peaks were better than for single peaks, and those for PSRV's better than for multiple peaks as evidenced by improvements in coefficients of determination. While scatter from one event to the next contributes to small coefficients of determination, an even greater effect is produced by differences in geology at the seven locations. Fits to the data can be used as prediction equations. Examination of waveforms of individual components of motion showed influences of topography at two locations. (ERA citation 07:049387)