seismograph [′sīz·mə‚graf]
Seismograph
an instrument that records oscillations of the ground caused by seismic waves.
A seismograph (Figure 1) consists of a seismometer—an instrument that receives the seismic signal—and a recording device. The basic part of the seismometer is a weight connected with the case of the instrument by elastic couplings, for example, a pendulum. The case of the instrument is rigidly fixed to the object being studied. When the object oscillates, inertia causes the weight to move relative to the case. In most modern seismometers, this movement is converted into an electrical signal, which is recorded, usually in analogue form, by a mechanical, photographic, or magnetic recorder. Coded digital recording is sometimes used to increase the dynamic range and for convenience in subsequent computer processing.
There are also simpler seismographs, in which the movement of the seismometer weight is magnified mechanically or optically and is recorded by a mechanical or photographic recorder.
D. P. KIRNOS
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