Thursday, 21 March 2019  


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Making Artifical Earthquakes

Photo: Detonation of depth charge in Puget Sound during a Carnegie Institution-Coast Guard-Office of Naval Research joint seismic experiment (July 1951)

The availability of Navy surplus explosives following World War II made possible DTM's study of the Earth's crust using explosion seismology starting in 1948. Initial studies centered on the Washington, DC area and the Appalachian highlands, with blasts detonated offshore or in abandoned quarries. Later expeditions reached locales as far-flung as the Yukon Territory and the high Andean Plateau of South America. Arrays of seismometers recorded the passage of seismic waves from these controlled rthquakes" through varying depths of the crust. The lower boundary of the crust, the Moho, was clearly defined in even the earliest shots, but the overlying crust showed a surprisingly complex velocity structure. The simple, classical model of an orderly sequence of horizontally-uniform crustal layers was rapidly demolished.