Surface Motions From Underground Explosiongs With Appendix A Response Spectrum Analysis Of Records From Events

Ground effects resulting from certain HARDTACK II underground explosions were measured by strong-motion and teleseismic seismographs from 2000 feet to distances of nearly 100 miles. In addition, many temporary seismographs were operated by a number of organizations to distances of nearly 2400 miles, and routine seismographs continued to operate on a world wide basis. Some of the results are given in this report. An energetic wave believed reflected from the surface near the source was recorded by some of the strong-motion seismographs. It is out of phase with the initial wave and follows it by about a quarter second. From the ground effects standpoint, the Blanca shot was equivalent to a magnitude 4.8 earthquake, and seismic energy contained in a wave 0.8 km. from the source is believed to contain about 0.4 percent of the yield energy. The Logan and Rainier shots were respectively equivalent to magnitude 4.5 and 4.1 earthquakes and corresponding seismic energies contained respectively 0.5 and 0.3 percent of the yield energy.