Constants of electromagnetic seismographs for the time integration of ground displacement

Abstract

Every electromagnetic seismograph provides a record in the high-frequency range proportional to the time integration of the ground displacement. An intentionally extending this part of the amplitude characteristic of the integrator can be achieved when the equivalent periods of the seismometer and galvanometer are equal by a suitable combination of the equivalent damping constants: for integrator A, D 1 =0.383 and D 2 =0.924, for integrator B, D 1 =D 2 =0.650. The partial constants required to carry this out are given in Tabs 1 and 2. The equivalent period of the system with a shorter partial period increases with increasing coupling, the most in comparison with broad-band seismographs with a constant sensitivity for displacement, velocity and acceleration. This is convenient for long-period seismographs, if the seismometer has a shorter partial period than the galvanometer. An extension of its effective period can be achieved without deteriorating the mechanical stability of the seismometer, however, the effective period of the galvanometer decreases simultaneously.