The four successive earthquakes that rocked the city in the wee hours of Monday should not come as a surprise to the city dwellers. Delhi and its adjoining areas fall in seismic zone IV, which according to the seismic zone map of India, is termed as a ‘Severe Intensity Zone’. The fact that two major lineaments (fractures), namely Delhi-Haridwar ridge and Delhi-Moradabad faults pass through Delhi and NCR, makes the territory all the more earthquake prone as both have the potential of generating earthquakes of high magnitude.
Zone IV, in which the Capital falls, has a fairly high seismicity where the general occurrence of earthquakes is of 5-6 magnitude, a few of magnitude 6-7 and occasionally of 7-8 magnitude. Besides, a seismic microzonation study of Delhi and NCR carried out by Indian Meteorology Department (IMD) has identified east and northeast Delhi area as most vulnerable because of newer alluvial soil type found in those areas.
The earthquake zoning map of India divides India into 4 seismic zones (Zone II, III, IV and V). Areas under Zone V (very severe intensity zone) - Western and Central Himalayas, North-East, Andaman and Nicobar Islands and the Rann of Kutch - have the highest level of seismicity. Delhi, Jammu and Kashmir, Indo-Gangetic basin, Koyna region of Maharashtra fall in Zone IV. A major part of India, 43 per cent of its total area, however, falls under Zone II, i.e., low intensity zone.