Deep seismic sounding with nuclear explosives in the soviet union.

A large geophysical program of exploration that uses deep seismic sounding has been under way in the Soviet Union for decades. Underground nuclear explosives have been used as strong seismic sources since 1971. The wide spacing between these seismic sources-for example, 500 kilometers-has permitted seismic exploration of inaccessible areas in traverses up to 3000 kilometers in length. During the same time an ultra-deep drilling program has also been under way. The data gathered have been used to elucidate details of the crust as well as to describe layering and inhomogeneities in the underlying mantle. By Soviet account, deep seismic sounding has been instrumental in confirming the existence of numerous sedimentary structures containing oil and gas fields in western and eastern Siberia.