Abstract

The underground nuclear explosions BENHAM, PURSE, JORUM, and HANDLEY, detonated on Pahute Mesa, initiated earthquake sequences lasting approximately 70, 10, 20, and 60 days, respectively. Earthquakes of magnitude 2.0 or larger in these sequences numbered 2012, 24, 159, and 231, respectively; earthquake magnitudes were all less than 5. The explosion PIPKIN, also detonated on Pahute Mesa, had no apparent effect on seismicity. Ninety-four per cent of the earthquakes with well-determined focal depths occurred at depths shallower than 5 km, and 95 per cent of the located earthquakes were within 14 km of ground zero of the preceding explosion. There is no evidence for explosion-stimulated earthquake activity extending outside the area of Pahute Mesa. The spatial distribution of earthquakes seems to be largely controlled by geological structure; however, the epicenter distribution can be correlated with observed fault movement only for aftershocks of HANDLEY. Fault-plane solutions indicate predominant dip-slip movement in the northern part of the Pahute Mesa area for aftershocks of BENHAM, JORUM, and HANDLEY. In the southern part, dextral strike-slip movement was found for aftershocks of BENHAM and HANDLEY. The frequency-magnitude relations are similar for earthquakes following BENHAM, PURSE, JORUM, and HANDLEY.

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