Seismographs are instruments that record seismic waves (waves caused by earthquakes). They are widely used to monitor natural disasters such as volcanoes and earthquakes. The data recorded by seismographs helps scientists predict future volcanic eruptions or earthquakes. Seismographs are devices that detect seismic waves generated by earthquakes. These waves travel through the earth at various speeds depending on their frequency. The speed of these waves can be measured using a device called a seismometer.