The regions far away from the Himalaya and other inter-plate boundaries, which were once considered to be relatively safe from strong shaking, have also experienced several devastating earthquakes. The huge loss of life and property in the earthquake-prone areas of the country have shown that the built-environment is extremely fragile, and country’s ability to respond to these events is extremely inadequate. Post earthquake damage survey revealed that 90 per cent of casualties result directly from the collapse of buildings that had usually no earthquake resistant features. Secondary events, such as landslides, fires, and tsunamis, account for the remaining 10 per cent of the casualties. Recent earthquakes in India have demonstrated the need for seismic risk evaluation of building stock and consequences of future earthquakes. The rapid growth of cities, unplanned habitat, faulty structural design and poor quality construction techniques have also contributed to the proliferation of seismic risk. Evaluation of seismic safety of these constructions and adopting requisite retrofitting measures is a challenging task for the national government. Almost the entire northeast region, northern Bihar, Himachal Pradesh, Jammu & Kashmir and some parts of Gujarat are in seismic zone V, while the entire Gangetic plain and some parts of Rajasthan are in seismic zone IV. In the last 20 years the country has experienced 8 major earthquakes that took more than 25000 lives and thereby significantly affecting the local and regional economy. The effect would be substantial if such earthquakes hit metro cities where inappropriate developmental activities are alarmingly high. After Latur (1993, magnitude(M) 6.3, 7928 deaths) earthquake, the state government undertook several post-earthquake risk reduction measures but the lesson has not been replicated in the neighbouring state of Gujarat till it was struck with a devastating earthquake (M6.9) in 2001, which took more than 13800 lives.
Potential earthquake threats in India: The collision of Indian and Eurasian plates gave way to the formation of the great Himalaya. The Indian plate is still penetrating deeper at an estimated rate of about 50mm/year, causing intense seismic activity in the entire region. Five major earthquakes (M>7.5) (1897 Assam, 1905 Kangra, 1934 Bihar-Nepal, 1950 Assam and 2005 Kashmir) and 484 moderate to major quakes in the Himalayan Frontal Arc during the past 110 years have demonstrated the vulnerability of the entire surrounding region to earthquakes. Various scenario analysis have indicated that more than 100 million people are at seismic risks of varying magnitudes in the towns and villages of the hilly areas of the north and north east and the entire Indus-Ganga-Brahmaputra plain. The Koyna earthquake (1967, M6.3) in the stable continental region of India occurred after the filling of the Shivaji Sagar Lake, which raised the issue of seismic safety of mega hydel projects in India.
Seismic Zoning: The regions of the country away from the Himalayas and other inter-plate boundaries were considered to be relatively safe from damaging earthquakes (Fig 1). However, in the recent past, even these areas have experienced devastating earthquakes. The Koyna earthquake in 1967 led to the revision of the seismic zoning map resulting in the deletion of the non-seismic zone from the map. The areas surrounding Koyna were also re-designated to Seismic Zone IV, indicating high hazard. The Latur earthquake in 1993 resulted in further revision of the seismic zoning map in which the low hazard zone or Seismic Zone I was merged with Seismic Zone II, and some parts of Peninsular India were brought under Seismic Zone III consisting of areas designated as moderate hazard zone areas. Considering the recorded history of earthquakes in the country, 11 per cent of the land area is in very high risk zone V, 18 per cent in high risk zone IV and 30 per cent moderate risk zone III. The capital cities of Guwahati and Srinagar are located in seismic zone V, while the national capital Delhi is in zone IV and the mega cities of Mumbai, Kolkata and Chennai are in zone III (A S Arya et. al. 2007 ‘Hazards, Disasters and your community’, under UNDP, Disaster Risk Management Programme). In fact 38 cities with a population of half a million and above each and a combined population of 40 million are located in these three regions.
End Note: Earthquakes pose unique challenges during each phase of the disaster management cycle (i.e., during preparedness, prevention, mitigation, response, rehabilitation and recovery). International experience has shown that the maximum gains from earthquake management efforts are secured by strengthening the pre-earthquake preparedness and mitigation efforts. Continuous improvements in structural and non-structural measures for earthquake risk reduction will improve seismic safety in India. Various agencies of the Indian government at the national, state, district and local levels have been carrying out specific tasks for the prevention, preparedness and mitigation of disasters and undertaking a holistic, coordinated and prompt response to any disaster situation.
*The article is based on a compilation from various sources.