Abstract

Aftershocks of seven large nuclear explosions that were detonated at the Nevada Test Site (NTS) from 1968 through 1976 have been modeled with with different aftershock decay functions. Four natural aftershock sequences from the area have also been studied. The aftershocks of nuclear explosions are different from most natural aftershocks, because they decay more rapidly, and their decay is more often fit by variants of exponential functions. The aftershocks of nuclear explosions generally have shallower focus than natural aftershocks, in keeping with the relatively shallow depths at which the nuclear explosions were detonated. Rapid decay is also observed in shallow-focus aftershocks of natural earthquakes near the Nevada Test Site, suggesting that conditions at the hypocenters of the aftershocks influence the temporal decay of aftershocks. A theory of aftershock decay proposed by Dieterich (1994) predicts more rapid decay at shallow depths and offers one possible explanation of the results. Because aftershocks of nuclear explosions decay rapidly, the activity currently observed in the Nevada Test Site has most likely decayed fully, and so the current level of activity should persist into the future.

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