SEISMOGRAPH

instrument that makes a record of the ground oscillations caused by an earthquake, explosion, or other Earth-shaking phenomenon. Although originally designed to record natural earthquakes, it has many other uses. An earlier seismic instrument called the seismoscope made no record of the ground oscillations but simply indicated that shaking had occurred. The term seismometer originally referred to an instrument that measures the amount of ground motion. Some seismographs are equipped with an electromagnetic device called a sensor that translates ground motions into electrical changes. A seismogram is a record made by a seismograph.