Recently, the Wadia Institute of Himalayan Geology (WIHG) has observed that the recent series of tremors in the National Capital Region-Delhi (Delhi-NCR) are not unusual and are indicative of strain energy build up in the region.
Seismic Zones in India
- There are four seismic zones (II, III, IV, and V) in India based on scientific inputs relating to seismicity, earthquakes occurred in the past and tectonic setup of the region.
- Previously, earthquake zones were divided into five zones with respect to the severity of the earthquakes but the Bureau of Indian Standards (BIS) grouped the country into four seismic zones by unifying the first two zones.
- BIS is the official agency for publishing the seismic hazard maps and codes.
Seismic Zone II:
- Area with minor damage earthquakes corresponding to intensities V to VI of MM scale (MM-Modified Mercalli Intensity scale).
Seismic Zone III:
- Moderate damage corresponding to intensity VII of MM scale.
Seismic Zone IV:
- Major damage corresponding to intensity VII and higher of MM scale.
Seismic Zone V:
- Area determined by pro seismically of certain major fault systems and is seismically the most active region.
- Earthquake zone V is the most vulnerable to earthquakes, where historically some of the country’s most powerful shocks have occurred.
- Earthquakes with magnitudes in excess of 7.0 have occured in these areas, and have had intensities higher than IX.
Seismic Waves, Richter Scale and Mercalli scale
- Seismic waves are the vibrations from earthquakes that travel through the Earth and are recorded on instruments called seismographs.
- Seismographs record a zigzag trace that shows the varying amplitude of ground oscillations beneath the instrument.
- The earthquake events are scaled either according to the magnitude or intensity of the shock.
- The magnitude scale is known as the Richter scale. The magnitude relates to the energy released during the earthquake which is expressed in absolute numbers, 0-10.
- The intensity scale or Mercalli scale takes into account the visible damage caused by the event. The range of intensity scale is from 1-12.