Classification of earthquake zones in India

Classification of earthquake zones in India

Question:- India being a large landmass is particularly prone to earthquakes. The bureau of Indian standards publishes Seismic Zoning Map based on inputs of geologists and scientists. Explain the classification and also how earthquake zones are determined?

- Classification of zones: The country has been divided into seismic zones based on the various scientific inputs from agencies including earthquake data provided by the Indian Meteorological Data. The most recent version of seismic zoning map of India assigns four levels of seismic activity for India in terms of zone factors. Amongst these, zone V is highly prone while zone II is the least.

- The zones have been classified by scientists and geologists in 1956 when a 3 zone seismic zoning map of India was produced. This map was based on earthquake distribution and geotectonics and the values of maximum MM intensities recorded in historic times.

- Location of zones: While the seismically highly prone zones are confined to plate boundaries like the Himalayan frontal arc in the north, Chaman fault region in north west and Indo- Burmese region in north-east, the least active zone is confined to Indian shield in the south and the moderate zone to the transitional zone between the two.

- The most vulnerable is zone 5 where in the past some powerful shocks have occurred. Earthquakes with magnitude of 7.0 have occurred and have the potential of more than 9.0.This zone includes all of north eastern India, Andaman Nicobar Islands, some parts of north western Bihar, eastern parts of Uttaranchal, Kangra Valley in Himachal Pradesh, Srinagar area in Jammu Kashmir and Rann of Kutch in Gujarat.

- Most of India lies in zone III wherein the maximum magnitude of 7 can be expected. New Delhi, Mumbai and Calcutta lie in zone IV and only Chennai lies in zone II.

- Large parts of south central India lies in zone I along with a small section stretching from eastern Rajasthan into northern Madhya Pradesh. Few areas of Orissa, Jharkhand and Chhatisgarh also lie in this zone.

Since zones II and I are located far from the Himalayan plate region, fewer or rarely earthquakes strike this region.

Facts and figures:

- Indian plate is driving into Asia at a rate of approximately 47 mm/year.

- The IS code assigns zone factor of 0.36 for Zone 5 and 0.24 for Zone 4.

- The IS code assigns zone factor of 0.16 for Zone 3.

- The Line of Actual Control (LAC) is the effective border between India and the People's Republic of China.