Seismic Zones of India: All you Need to Know
Krunal Lad is a Head of Structural Engineering Department at SDCPL. He is a Senior Manager (Structure)at SDCPL. He gained his Master Degree in Structural Engineering (Civil) from Pune University in 2011. He is responsible for structural design of all types of structures including residential, commercial, industrial, infrastructure, educational, health, etc. He is a blogger at gharpedia.com. You can reach him via LinkedIn, Twitter.
Every nation carries out mapping of its territory based on all natural disasters like earthquake, cyclone, flood and volcano etc.. This mapping is done on the basis of past history and factors responsible for such disaster of present in that area. This mapping helps people to design their home and other infrastructure so that they don’t become the victim of such disaster and can withstand disasters with as minimum as possible loss of life and property. Code of practice of all nations for design of buildings and other structure recommended design guidelines based on such mapping or zoning.
Hence one who is designing a home must take into consideration the effect of such disaster and make suitable provision in its structural design. One must consult his/her architect/structural designer to include such provision based on the zoning.
In India, the country has been divided into 4 zones. Earlier there were 5 zones however after Bhuj Earthquake of 2001, the zone I have been eliminated. Each country in the world has such zoning for all such natural disasters. India is divided into 4 seismic zones i.e. Zones II, III, IV and V. These zones are divided on the basis of Maximum Considered Earthquake and service life of structure in each seismic zone.
Seismic zone have been categorised as follows:
The areas of this zone have the highest risk of effects by an earthquake. The earthquake intensity for this zone is MSK-IX or greater. The zone factor for this zone is 0.36, which is indicative of effective (zero period) level earthquake in this zone. This zone is called as Very High Damage Risk Zone. Some of the regions which fall under this zone are Rann of Kutch, Eastern regions etc.
Difference between Intensity & Magnitude of Earthquake
Intensity is number written in Roman numeral describing the severity of the earthquake in terms of its effect on earth surface, and on human and their structure. The higher the number, the higher the intensity of the effect/damage. While magnitude indicates amount of energy released at the source i.e. epic center.
Intensity is measured as MMS (modified Meracallie Scale) while magnitude is measured on richter scale.
The areas of this zone have the lesser risk to effects by an earthquake as compared to zone V. The earthquake intensity for this zone is between MSK VIII to MSK-IX. The zone factor for this zone is 0.24. This zone is called as High Damage Risk Zone. Some of the regions which fall under this zone are Northern regions, North Eastern regions, Delhi etc.
The areas of this zone have the lesser risk by an earthquake. The earthquake intensity for this zone is MSK VII. The zone factor for this zone is 0.16. This zone is called as Moderate Damage Risk Zone. Some of the regions which fall under this zone are some parts of Gujarat & Maharashtra, Andaman Nicobar Islands etc.
The areas of this zone have the least risk of an earthquake. The earthquake intensity for this zone is MSK VI. The zone factor for this zone is 0.10. This zone is called as Low Damage Risk Zone. Larger parts of India come under this zone.
One can see that in zone II, the intensity is VI on M scale while in zone V it is iX or greater, i.e. the damage and effect would be higher.