What is seismograph? Explain its construction and functioning. 

The tremors produce waves on the surface of the earth. These are called seismic waves. The waves are recorded by an instrument called the seismograph the instrument is simply a vibrating rod, or a pendulum which starts vibrating when tremors occur. A pen is attached to the vibrating system. The pen records the seismic waves on a paper which moves under it. By studying these waves scientist can construct a complete map of the earthquake and they can also estimate the energy associate with the earthquake which determines is power to cause destruction.