A seismograph has the to locate and measure the source of earthquakes. If an earthquake occurs waves are created which travel through the Earth. This then generates vibrations in the ground as they journey towards the surface. The seismograph is sensitive to these vibrations employing a large bulk with a high inertia to detect the waves movement. The bulk does not move, but the detectors move in relation to it. There are many types of seismograph. The more technical forms have electromagnetic detectors. The basic form is called the simple or pendulum seismograph.
The pendulum seismograph consists of three mounted pendulums. One records the vertical vibrations received, and the other two gather information on the horizontal tremors found in two directions at right angles to each other. These vibrations do not actually set the pendulums swinging, but instead the paper beneath moves, attached pens record the vibrations.
Seismographs are so sensitive they can detect the small tremors leading to an earthquake before they are felt by humans, giving a certain degree of warning against impending disaster.
