Records of particle velocity in the free-field geological environment near underground nuclear explosions may be interpreted to yield the energy flux at a measuring station near or within the region of elastic response of the rock. Such data from 21 events in several types of rock have yielded energy fluxes. Total energies associated with the motion propagated into the seismic region have been derived from all but seven of these. The total energies are a measure of the seismic-source strength, and the ratios of these energies to those released by the explosion are measures of the energy coupled into the Earth as seismic motion.

Explosions in granite, dolomite, or wet tuff produce seismic sources of the order of 2 per cent of the explosively released energy. Similar explosions in porous rocks such as dry tuff and desert alluvium provide seismic sources an order of magnitude weaker than those in hard or wet rock.

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