In the last week, North India witnessed several Earthquakes. Bikaner has been jolted by earthquakes of magnitude 5.3 while the ones felt in Hyderabad were of 4.0 magnitude. Now as per the recent seismic mapping, 59 percent of the country is prone to earthquakes of different intensities. According to the seismic zoning map of India given by Minister of Earth Science, Dr. Jitendra Singh in Lok Sabha, the total area of the country is classified into four major seismic zones.

What are Seismic Zones?

A seismic zone is an area in which earthquakes are most likely to occur. For example, the New Madrid Seismic Zone in the Central United States is more prone to earthquakes than any of its neighboring places. Under this classification comes a seismic hazard zone. It describes an area with a particular level of hazard due to earthquakes.

How does an earthquake occur?

There are continuous slow movements in the tectonic plates, but they get stuck at their edges due to friction. When this stress on the edge overcomes the friction, there occurs an earthquake. The energy released is in form of waves that travel through the earth’s crust and cause the shaking that we feel.

Seismic Zones of India

The classification of seismic zones in our country is based upon the empirical seismic attenuation law corroborated with historical seismicity and ground motions of the earthquakes. In India, there are four major seismic zones. Amon these, Zone V is seismically the most active region while zone II is the least. Nearly 11 percent of the country falls in zone V, 18 percent lies in zone IV, 30 percent in zone III, and the rest lies in zone II.

The National Centre for Seismology (NCS) works to maintain a National Seismological Network (NSN) which consists of 115 observatories spread across the country. These observatories detect any movement that occurs under the surface and disseminate them to the center and state disaster authorities so that they can ensure preparedness and can conduct rescue and rehabilitation work if the tremors hit.

In February this year, the government had said that 965 earthquakes of magnitude 3 and above were recorded in 2020. Among these, 13 of them were in the National Capital Region and its nearby areas.

List of most seismically active cities

The cities included in the most active zone V are Bhuj, Darbhanga, Guwahati, Tezpur, Srinagar, Sadiya, Port Blair, Mandi, Kohima, and Jorhat.

Cities that fall in zone IV are Almora, Jalpaiguri, Kolkata, Ludhiana, Monghyr, Moradabad, Patna, Parganas, Pilibhit, Shimla, Roorkee, Ambala, Amritsar, Bahraich, Barauni, Bulandshahr, Chandigarh, Darjeeling, Dehradun, Deoria, Delhi, Dinajpur, Ghaziabad, Gangtok, and Gorakhpur.

Previously, the Ministry of Earth Sciences was under Harsh Vardhan. He had said that the NCS had initiated a magnetotelluric geophysical survey, interpretation of satellite imageries, and geological field investigations in Delhi and surroundings in collaboration with IIT Kanpur to locate and characterize the major seismic sources or fault lines in Delhi and surrounding regions.

The center is also considering seismic microzonation of cities in India having a population of 5 lakh to incorporate the data into better urban planning. The development will give inputs for constructing earthquake-resilient buildings to reduce the impacts of tremors and minimize the loss of lives and property.