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War-time applications of geophysics come under the heading of military operations and location of essential minerals. In the combat zone, sound ranging helps to locate hostile guns and to adjust friendly artillery. Listening devices determine the approach of submarines or airplanes. Buried munition dumps, shells, and bombs can be located by radio detection devices. Vessels at sea may establish their position by radio-acoustic ranging. Planning of fortifications and harbors and location of construction materials will be aided by seismic refraction, electrical resistivity, and dynamic ground testing. The same methods are applicable to problems involving the construction of railroads, highways, bridges, tunnels, and munitions plants. For the last, added protection is possibl by static-ground-resistance investigations. Salvage operations, location of shipwrecks and practice weapons, are aided by echo-sounding and radio methods.
In the second group, geophysics is concerned with the location of water, fuels, and strategic minerals. Water may be found under favorable conditions by electrical and seismic methods, and water wells may be tested by electrical logging. Geophysical foundation investigations are applicable in irrigation, flood-control, and power projects. Magnetic, gravimetric, seismic-reflection, and electrical well-logging methods occupy a prominent place in oil exploration. Coal and lignite deposits may be mapped by geophysical methods. Magnetic, electrical, gravimetric, and seismic exploration methods are now used in a systematic government-sponsored exploration program to uncover vitally needed deposits of bauxite, chromite, manganese, mercury, nickel, tin, and tungsten.
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