Designing Safe House in an Earthquake Prone Area
India on account of unique geo-physical setting is highly prone to earthquakes of varying intensities. The country has faced several devastating earthquakes in the past resulting in a large number of deaths and severe property damage. During the last century, five earthquakes measuring M8 or more had struck different parts of the country; Great Assam earthquake (1897), Kangra earthquake (1905), Bihar-Nepal earthquake (1934), Andaman-Nicobar earthquake (1941) and Assam earthquake (1950) had caused untold misery to the affected community and enormous damage to infrastructure and public and private property. In the recent years damaging earthquakes had been experienced in different parts of the country (Table 1) e.g. Assam (1988) M7.2, Bihar- Nepal (1988) M6.5, Uttarkashi (1991) M6.6, Latur (1993) M6.4, Jabalpur (1997) M6.0, Chamoli (1999) M6.8 and Bhuj (2001) M6.9. Some of the earthquake events (Muzaffarabad earthquake, 2005 M7.6; Great Sumatra earthquake, 2004 M9.1), which did occur outside Indian Territory, had a very severe bearing on the nation as well. Table -1, shows region wise frequency of occurrence of earthquakes for last 110 years.
The country has been classified into different zones indicating the intensity of damage or frequency of earthquake occurrences. These zoning maps indicate broadly the seismic coefficient that could generally be adopted for design of buildings in different parts of the country. These maps are based on subjective estimates of intensity from available information on earthquake occurrence, geology and tectonics of the country. The Indian seismic zoning is a continuous process which keeps undergoing changes as more and more data on occurrence of earthquakes becomes available.
Considering the recorded history of earthquakes in the country, seismologists have classified 59% of the land mass of India as prone to earthquakes of different magnitudes - 11% in very high risk zone V, 18% in high risk zone IV and 30% moderate risk zone III. The capital cities of Guwahati and Srinagar are located in seismic zone V, while national capital of Delhi is in zone IV and the mega cities of Mumbai, Kolkata and Chennai are in zone III. 38 cities with population of half a million and above each and a combined population of million are located in these three regions.
List of Indian standards dealing with Earthquake resistant construction are:
The following links give brief guidelines for constructing safe houses in various areas lying in different seismic zones of the country and also about retrofitting etc.