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Thursday, October 21, 2021

High-risk seismic zones in India: How prone is your city to earthquakes

The National Disaster Management Authority and Bureau of Indian Standards classified 38 cities in India to be in high-risk seismic zones.

By: Express Web Desk | New Delhi |
September 21, 2017 6:28:52 pm
Indian soldiers and locals remove debris from a damaged building after an earthquake in Imphal, capital of the northeastern Indian state of Manipur, Monday, Jan. 4, 2016. A 6.7 magnitude earthquake hit India’s remote northeast region before dawn on Monday. (AP Photo)

The National Disaster Management Authority and Bureau of Indian Standards classified 38 cities in India to be in high-risk seismic zones. Incidents like the massive earthquake that struck Mexico on Tuesday, which resulted in a huge loss to life and property, raises the question — how prone are Indian cities to earthquakes and how prepared are we to deal with them?

India has a dubious record when its comes to designing its structures with earthquake safety in mind as several instances in the past suggest.

Earthquakes are caused due to tectonic shifts below the earth surface. India’s case is quite serious as the Indian subcontinental plate grinds against the Asian continental plate. India cities, particularly towards the north and closer to the Himalayas, face a bigger threat.

While the numbers on the richter scale only measure the amplitude of the shockwaves on a seismogram, a comparison of strength can be calculated using scientific methods. According to a model employed by the United States Geological Survey, an earthquake measuring 8.7 on the richter scale is 22,387 times stronger than one measuring 5.8.

Due to the country’s topography, it is important to classify the regions into seismic zones with respect to the likelihood of an earthquake occurring in the region. These seismic zone maps are revised from time to time.

The Bureau of Indian Standards has classified regions in India into four seismic zones on the basis of historical seismic activity. These are zones II, III, IV and V. Among these, Zone V is the most seismically active region and zone II is the least active. According to Modified Mercalli scale, the seismic zone intensity are classified as zone II (low intensity zone), zone III (moderate intensity zone), zone IV (severe intensity zone) and zone V (very severe intensity zone).

According to the Ministry of Earth Sciences, Zone V includes entire northeastern India, parts of Jammu and Kashmir and Himachal Pradesh, Uttaranchal, Rann of Kutch in Gujarat, parts of North Bihar and Andaman & Nicobar Islands.

Zone-IV includes the remaining parts of Jammu and Kashmir and Himachal Pradesh. Delhi-NCR region, Sikkim, northern parts of Uttar Pradesh, Bihar and West Bengal, parts of Gujarat and small portions of Maharashtra near the west coast and Rajasthan also fall in this zone.

Regions under zone III are Goa, Kerala, Lakshadweep, remaining parts of Uttar Pradesh, Gujarat and West Bengal, parts of Punjab, Rajasthan, Madhya Pradesh, Bihar, Jharkhand, Chhattisgarh, Maharashtra, Orissa, Andhra Pradesh, Tamilnadu and Karnataka.

The remaining portion of the country falls under zone II.

The 38 cities classified were analysed among those that have a population of over 0.5 million.

According to the government analysis and seismic revision, major cities under earthquake threat are:
Zone V cities– Guwahati and Srinagar (zone V)
Zone IV cities — Delhi, Patna, Dehradun, Jamnagar, Meerut, Jammu, Amritsar and Jalandhar
Zone III cities — Ahmedabad, Vadodara, Surat, Rajkot, Bhavnagar, Pune, Bhiwandi, Nashik, Greater Mumbai, Thane, Bhubaneswar, Cuttack, Chennai, Asansol, Coimbatore, Agra, Varanasi, Bareilly, Lucknow, Kanpur, Kolkata, Indore, Jabalpur, Vijaywada, Dhanbad, Mangalore, Kochi, Kozhikode, Trivandrum.

The threat is as real as it gets and preparedness is the only solution to avert something that is beyond human control. Although none of the metropolises have been hit by major quake in India recently, the potential devastation it could cause is catastrophic.

In 1905, Kangra was hit by a magnitude 8.6 quake that killed at least 19,000 people. A temblor that hit Bihar in 1934 at magnitude 8.4 shook buildings from Mumbai to as far as Lhasa. The destruction in Bihar was overwhelming. At least 11,000 people were killed. Mahatma Gandhi had infamously said that the quake was a punishment for the sin of practicing untouchability.

Assam was hit in 1950 with one of the biggest quakes in the Himalayas at magnitude 8.5. Over the decades that followed, a magnitude 6.6 quake that hit Bihar-Nepal in 1988 killed over 1,000 people. Latur was hit in 1993m killing 7,928 people. The quake that hit Bhuj in Gujarat in 2001 killed at least 13,800 people.

The root of the problem lies with the non-enforcement of regulations to make buildings and structures earthquake-proof. The Bureau of India Standards in 1962 released the Indian Standard Criteria for Earthquake Resistant Design (revised in 2005). Infrastructure projects like Metros, flyovers, dams etc are built keeping these standards in mind. The glass ceiling is implementation of these standards in building residential and commercial buildings.

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