Seismic waves from the underground atomic explosion of September 19, 1957, were recorded for 45 minutes on multichannel magnetic tape at a point 25 miles north of Holbrook, Arizona, about 370 miles from their source. Twelve vertical-component seismometers were laid out in the form of an L 5,280 ft. by 1,600 ft. to permit determinations of apparent velocity and of direction of arrival. The frequency range recorded, about 6 to 40 cps, was higher than usual in earthquake seismology. During tape playback, supplementary filtering, gain adjustments, and changes in time scale served to improve the quality and legibility of the records.
The playback seismograms reveal strikingly well not only to Pn and P* waves transmitted and refracted by the crust, but also many others as well. Some of these, as clearly indicated by their directions of arrival, did not originate from the explosion. We have attempted only an elementary interpretation, our main purpose being to make the data available to anyone who might be interested in them. The relatively short wave lengths of the recorded events may make them of unusual significance. In addition to arrival times, we made a few measurements of absolute amplitude and of frequency spectra.