Earthquake Seismographs and Associated Instruments

Abstract

This chapter focuses on earthquake seismographs and associated instruments. Progress in seismograph instrument development in the past quarter century has been quite rapid. One of the first of the new instruments was the torsion seismograph invented by J. A. Anderson and developed jointly by him and H. O. Wood. Direct-recording pendulum seismographs, having periods greater than about 4 seconds, are severely limited as to their maximum useful magnification because of their high sensitivity to earth tilts in the case of the horizontal-component instruments, and to thermal response of the spring in the case of the vertical-component instruments. It is possible to eliminate these long-period drifts by means of a viscous coupling between the pendulum and the optical or mechanical recording elements. Such an instrument was first described by Arnold Romberg. One of the first effective modifications of the moving-conductor transducer (Galitzin) seismograph was made by B. Gutenberg. He shortened the period of the pendulum to 3 seconds (by tilting the base) and increased the magnetic field strength by decreasing the air gap clearance. This resulted in a frequency-response characteristic with higher magnifications for the short-period waves than the standard Galitzin or any other instrument in use at that time. This chapter discusses other such devices as: the variable reluctance electromagnetic pendulum seismograph, electrostatic transducer pendulum seismographs, carrier-current transducer seismographs, linear strain seismograph, remote recording seismographs, and various components present in a seismograph. This chapter ends with the discussion of various seismograph response characteristics.