Seismographs are instruments used to record and measure earthquakes.
During an earthquake, vibrations initiated by the breakage of rock along the fault zone radiate outward from the point of fracture. Seismographs detect, amplify, and record these vibrations. The visual record produced by a seismograph is called a seismogram. The motion of the earth during an earthquake is measured in terms of its movement relative to some object that remains independent of the ground motion. In a seismograph this object consists of a mass suspended on springs within a case.