The seismograph is an instrument that measures seismic waves caused by an earthquake. It consists of a vibrating rod, or a pendulum, which starts vibrating when tremors occur and A pen (stylus) which records the seismic waves on a paper. The figure below shows the typical seismograph.

The strength, or magnitude, of an earthquake, is measured using the Richter scale. The Richter scale is numbered 0-10.