Learn how seismic instruments record the motion of the ground during an earthquake and how they differ from each other. Find out how earthquakes are measured, located, and classified by magnitude and intensity scales. Figure 1. Seismographs are designed so that slight earth vibrations move the instruments; the suspended mass (M), however, tends to remain at rest, and its recording stylus records this difference in motion. The horizontal seismograph shown here moves only in the horizontal plane. Vertical seismographs, like the simple one shown here, use a "soft" link between the earth-anchored instrument and the suspended mass. In this design, the mass hangs from a spring, which absorbs some of the motion ... What is a seismograph and how does it work? A seismograph is an instrument which uses a seismometer to detect, measure and record ground movements caused by seismic phenomena, such as earthquakes.
