Earthquake hazard zoning of India
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The Indian haseeb subcontinent had a long history of devastating earthquakes. The major reason for the high frequency and intensity of the earthquakes is that India continues to drive into Asia at a rate of appromately 47 mm/year[1]. Geographical statistics of India show that almost 54% of the land is vulnerable to earthquakes. The latest version of seismic zoning map of India given in the earthquake resistant design code of India [IS 1893 (Part 1) 2002] assigns four levels of seismicity for entire India in terms of different zone factors. In other words, the earthquake zoning map of India divides India into 4 seismic zones (Zone 2, 3, 4 and 5) unlike its previous version which consisted of five or six zones for the country. According to present zoning map, Zone-5 expects highest level of seismicity whereas Zone-2 is associated with lowest level of seismicity. The latest seismic zoning map can be accessed from INDIA METEOROLOGICAL DEPARTMENT website ([1]).
The MSK (Medvedev-Sponheuer-Karnik) intensity broadly associated with the various seismic zones is VI (or less), VII, VIII and IX (and above) for Zones-2, 3, 4 and 5, respectively, corresponding to Maximum Considered Earthquake (MCE). The IS code follows a dual design philosophy: (a) under low probability or extreme earthquake events (MCE) the structure damage should not result in total collapse, and (b) under more frequently occurring earthquake events, the structure should suffer only minor or moderate structural damage. The specifications given in the design code (IS 1893: 2002) are not based on detailed assessment of maximum ground acceleration in each zone using deterministic or probabilistic approach. Instead, each zone factor represents the effective period peak ground accelerations that may be generated during maximum considered earthquake ground motion in respective zone. Each zone indicates effects of an earthquake at a particular place based on the observations of the affected areas and can also be described using a descriptive scale like Modified Mercalli intensity scale[2] or the Medvedev-Sponheuer-Karnik scale[3].
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[edit] Zone 5
Zone 5 is the worst prone zone in the country. It covers the area with the highest risk zone that suffers earthquakes of intensity MSK IX or greater. The IS code assigns zone factor of 0.36 for Zone-5. Structural designer uses this factor for earthquake resistant design of structure in zone-5. The zone factor of 0.36 is indicative of effective (zero period) peak horizontal ground accelerations of 0.36 g (36 % of gravity) that may be generated during MCE level earthquake in this zone. It is referred to as the Very High Damage Risk Zone. The state of Kashmir, the western and central Himalayas, the North-East Indian region and the Rann of Kutch fall in this zone Generally the areas having trap or basaltick rock are prone to earth quake.
[edit] Zone 4
This zone is called the High Damage Risk Zone and covers areas liable to MSK VIII. The IS code assigns zone factor of 0.24 for Zone-4. The Indo-Gangetic basin,Rajasthan region and the capital of the country(Delhi) fall in Zone 4.
[edit] Zone 3
The Andaman and Nicobar Islands, parts of Kashmir, Western Himalayas and Punjab fall under this zone. This zone is classified as Moderate Damage Risk Zone which is liable to MSK VII. The IS code assigns zone factor of 0.16 for Zone-3.
[edit] Zone 2
This region is liable to MSK VI or less and is classified as the Low Damage Risk Zone. The IS code assigns zone factor of 0.10 (maximum horizontal acceleration that can be experienced by a structure in this zone is 10 % of gravitational acceleration) for Zone-2.
[edit] Notes
- ^ Earthquake Hazards and the Collision between India and Asia. Retrieved on 2006-05-13.
- ^ Vulnerability Zones in India. Retrieved on 2006-05-13.
- ^ Lessons learned from the Gujarat earthquake - WHO Regional Office for South-East Asia. Retrieved on 2006-05-13.
