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a receiver for sound waves that propagate through the upper layers of the earth’s crust. It consists of a housing containing a heavy weight mounted elastically between two thin, flexible metallic plates. The acoustic vibrations that are propagating through the ground cause the housing—which is in contact with the ground—to move whereas the heavy weight, because of its inertia, remains motionless.
In earlier geophone designs the inert mass was attached to a diaphragm that divided the inside of the housing into two sections; the displacements of the diaphragm relative to the housing produced alternate compressions and rarefactions on both sides that were transmitted through tubes to the ears of the observer. Modern geophones (prospecting seismographs) are equipped with electromechanical transducers (which convert ground vibrations into electrical current oscillations), an amplifier, and a recording loop oscillograph. They are used in acoustic prospecting for minerals, in military actions to listen to sappers’ operations, and in mine rescue operations. Geophones that function on the vibrograph principle are frequently used. Geophones using a piezoelectric quartz crystal as the basic element to detect acoustic waves of a specific length are called piezogeophones.