AFTERSHOCKS OF NUCLEAR-EXPLOSIONS COMPARED TO NATURAL AFTERSHOCKS

Aftershocks of seven large nuclear explosions that were detonated at t he Nevada Test Site (NTS) from 1968 through 1976 have been modeled wit h with different aftershock decay functions. Four natural aftershock s equences from the area have also been studied. The aftershocks of nucl ear explosions are different from most natural aftershocks, because th ey decay more rapidly, and their decay is more often fit by variants o f exponential functions. The aftershocks of nuclear explosions general ly have shallower focus than natural aftershocks, in keeping with the relatively shallow depths at which the nuclear explosions were detonat ed. Rapid decay is also observed in shallow-focus aftershocks of natur al earthquakes near the Nevada Test Site, suggesting that conditions a t the hypocenters of the aftershocks influence the temporal decay of a ftershocks. A theory of aftershock decay proposed by Dieterich (1994) predicts more rapid decay at shallow depths and offers one possible ex planation of the results. Because aftershocks of nuclear explosions de cay rapidly, the activity currently observed in the Nevada Test Site h as most likely decayed fully, and so the current level of activity sho uld persist into the future.