Deep-Well Variable-Reluctance Seismometer

A short-period variable-reluctance type seismometer, suitable for use in deep wells, has been developed. Electrical and mechanical characteristics are similar to the standard Benioff vertical seismometer. The deep-well seismometer is 5 inches (12.7 cm) in diameter and has a length of 10 feet (3 m). It consists of a spring-mass system, a variable-reluctance transducer, locking and unlocking provisions for the mass system, and an internal calibrator. The inertial mass, weighing 100 Kg, has a natural, undamped period of 1.0 sec. When used with a galvanometer-phototube amplifier, magnifications of earth motion of the order of 10at 1 cps are possible. For routine use, the system response is peaked between 2 and 3 cps.