Seismogram

seismogram

[′sīz·mə‚gram]

(engineering)

The record made by a seismograph.

Seismogram

 

the record produced by recording seismic oscillations with a seismograph. Recording techniques differ. The most common type of record is made on photosensitive paper using a light beam reflected from a small mirror on the pendulum of the seismometer or galvanometer. A record can also be made by pen point on smoked paper, by pen and ink on ordinary paper, and by a heated needle on chemically treated paper. Equipment is now being built that will make it possible to record seismic oscillations in digital code on magnetic tape; such data can then be fed into a computer.

International designations based on Latin names have been adopted to describe seismograms. Precise time marks are entered on the seismogram parallel to the record of oscillations; the length of a 1-min line on a seismogram may vary from 10 mm to a few millimeters, depending on whether the record is of short-period oscillations (as in seismic exploration) or long-period oscillations (as from remote earthquakes). Seismograms are used to establish the arrival time of various seismic waves at the observation point; the time of an earthquake’s occurrence and the location of the focus are determined from seismic travel-time curves. The magnitudes of amplitudes and periods of oscillations are used in determining the energy of an earthquake (the magnitude) and the intensity of oscillation at the observation point. The record of the wave picture from an earthquake or explosion reveals the structure of the medium through which the seismic waves are propagated.

I. V. GORBUNOVA