Class 8 Physics Some Natural Phenomena Measurement of Earthquake

Measurement of Earthquake

A device called Seismograph is used to record seismic waves produced during earthquakes on the surface of the earth. The purpose is to measure the motion or movement of ground during an earthquake

  • Seismograph are generally connect to bedrocks which are considered comparatively more stable to earthquakes than buildings, other concrete structures, trees etc
  • In order to ensure that the seismograph itself is stable and does not shake we tie a heavy weight (like a pendulum shown here) to the seismograph body.
  • When the ground shakes, the pendulum shakes and the pen begins to write on the paper on the rolling drum. As the drum rotates, the pen continues to write like a waveform.
  • Then the waveform which similar to what is shown in the figure is analysed to determine the magnitude of earthquake
  • The power of an earthquake is expressed in terms of a magnitude on a scale called Richter scale.
  • Destructive earthquakes generally have a magnitude of greater than 7 or 7.5. Earthquakes of magnitude 5-7 are moderate and below 5 are small or negligible.

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