Preliminary study of first motion from nuclear explosions recorded on seismograms in the first zone

Crustal Studies Technical Letter 13
In cooperation with the Defense Advanced Research Projects Agency
By:  and 



The U.S. Geological Survey has recorded more than 300 seismograms from more than 50 underground nuclear explosions. Most were recorded at distances of less than 1,000 km. These seismograms have been studied to obtain travel times and amplitudes which have been presented in reports on crustal structure and in a new series of nuclear shot reports. This report describes preliminary studies of first motion of seismic waves generated by underground nuclear explosions. Visual inspection of all seismograms was made in an attempt to identify the direction of first motion, and to estimate the probability of recording detectable first motion at various distances for various charge sizes and in different geologic environments. In this study, a characteristic pattern of the first phase became apparent on seismograms where first motion was clearly recorded. When an interpreter became familiar with this pattern, he was frequently able to identify the polarity of the first arrival even though the direction of first motion could not be seen clearly on the seismogram. In addition, it was sometimes possible to recognize this pattern for secondary arrivals of larger amplitude. These qualitative visual observations suggest that it might be possible to define a simple criterion that could be used in a digital computer to identify polarity, not only of the first phase, but of secondary phases as well. A short segment of recordings near the first motion on 56 seismograms was digitized on an optical digitizer. Spectral analyses of these digitized recordings were made to determine the range of frequencies present, and studies were made with various simple digital filters to explore the nature of polarity as a function of frequency. These studies have not yet led to conclusive results, partly because of inaccuracies resulting from optical digitization. The work is continuing, using an electronic digitizer that will allow study of a much larger sample of more accurately digitized data.

Additional publication details

Publication type Report
Publication Subtype USGS Unnumbered Series
Title Preliminary study of first motion from nuclear explosions recorded on seismograms in the first zone
Series title Crustal Studies Technical Letter
Series number 13
DOI 10.3133/70039490
Year Published 1963
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Earthquake Science Center
Description 19 p.; ill.; map
First page 1
Last page 19
Country United States
Online Only (Y/N) Y
Additional Online Files (Y/N) N
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