Surface Motions From An Underground Explosion

Seismic effects of Rainier, a 1.7-kt nuclear shot detonated 900 feet underground, were measured in terms of ground surface motion at ten strong-motion seismograph stations located 1200 to 45,000 feet from the source. In addition, records were borrowed from seven teleseismic stations located 100 to 300 miles from the source. Recorded accelerations attenuated from a maximum singlecomponent value of 2.6 g at 1280 feet to 0.009 g at 17,640 feet. Gutenberg-Richter magnitude of Rainier, calculated as for a natural earthquake from seven WoodAnderson seismograph records, was 4.6. Earthquakes of 4.6 magnitude are felt up to 60 miles from the epicenter, however, Rainier was felt by only a few observers at 21/2 miles. Seismologists at established teleseismic stations were able to pick out Rainier's elastic wave signature on seismograms at considerable distance. Very small amplitude waves from Rainier were found on the Coast and Geodetic Survey, College, Alaska, seismogram, 3600 km away, although attempts in the eastern United States at distances of 2000 to 3000 km, using conventional instruments, were not successful.