seismograph

Seismograph is an older term for what today is referred to as a seismometer. Seismometers are instruments used to measure waves and movement within the earth’s surface. These waves can be produced by natural occurrences like earthquakes and volcanic eruptions, or by artificial means such as excavation work and the detonation of explosive devices. Seismometers record these waves on a seismogram, with the resulting variegation in the lines produced indicating the relative power, or size, of the earthquake.