Abstract
ON May 1, 1969 a seismic event occurred in East Kazakhstan which, on the widely accepted body wave magnitude (mb): surface wave magnitude (Ms) criterion1,2, would be identified as an explosion; mb = 4.9 and Ms = 2.4 (ref. 3), giving a difference of 2.5, which is typical of explosive sources. For earthquakes Mb – Ms is usually less than 1.0 magnitude unit. At several teleseismic stations the P seismograms from this event recorded two clear arrivals separated by 7.5 s, which might indicate two explosions fired in succession. At some of these stations, however, the second arrival is clearly of opposite polarity to P and is thus probably the surface reflection pP, indicating a depth of focus of about 25 km. As this depth is outside the range of routine drilling techniques the event has been tentatively identified as an earthquake3. We show here that it definitely was an earthquake.
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References
SIPRI, Seismic Methods of Monitoring Underground Explosions, (International Institute for Peace and Conflict Research, Stockholm, 1968).
Marshall, P. D., and Basham, P. W., Geophys. J. R. astr. Soc., 28, 431 (1972).
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Douglas, A., Corbishley, D. J., Blamey, C., and Marshall, P. D., Nature, 237, 26 (1972).
Douglas, A., Marshall, P. D., Young, J. B., and Hudson, J. A., Geophys. J. R. astr. Soc., 36, 227 (1974).
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DOUGLAS, A., MARSHALL, P., YOUNG, J. et al. Seismic source in East Kazakhstan. Nature 248, 743–745 (1974). https://doi.org/10.1038/248743a0
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DOI: https://doi.org/10.1038/248743a0
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