Earthquakes: How safe are buildings in India?
Vibha Sharma
Chandigarh, February 10
Two devastating earthquakes measuring 7.8 and 7.5 in magnitude flattened multiple buildings, killing thousands of people across southern Turkey and northern Syria.
According to reports, some of the new buildings also crumbled under the impact, raising questions about building safety standards in Turkey. Ideally, technology and building rules should have ensured that buildings withstand earthquakes of higher magnitudes.
Seismicity and Indian subcontinent
While there have been several minor/moderate quakes in the region, the last devastating episode in the series in the Indian subcontinent were the two back-to-back shockers measuring 7.8 and 7.3 on the Richter followed by several high-intensity ones in April 2015.
They caused damage worth $10 billion, killing around 9200 persons according to the available data in Nepal.
The subcontinent is sitting on the highly seismic Indian plate, with some major fault lines.
Active thrust faults exist all across foothills in North India, the North-East and into northern Pakistan. Major faults exist from North-West to East and the North-East in India.
Some of the faults re in the 1905 Kangra earthquake measuring 8 on the Richter scale and the 1934 along Bihar-Nepal Border measuring 8.4.
Experts say that there is no seismically safe zone in India.
The Indian plate is one of the 12 major plates locked together to the surface of the earth like a jigsaw puzzle.
The Indian plate boundary has become very active of late and is gradually moving, pushing against the Eurasian plate by 4 to 5 cm every year.
If the recent incidents in Joshimath are any indication, mountains are becoming increasingly restless.
In the North, areas south of the Himalayas and Indo-Gangetic plains, including parts of Punjab, Haryana, Himachal, Delhi, Uttaranchal and Uttar Pradesh, are vulnerable.
With many areas in the high seismic activity zones IV and V, this should be a major cause of worry for the planners.
Seismic zones
India is divided into four seismic zones —Zone-II to Zone V.
Very high risk Zone V with the highest seismic intensity comprises the north-eastern areas, parts of Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Rann of Kutch and north Bihar.
High risk Zone-IV covers the remaining parts of Jammu & Kashmir and Himachal Pradesh, Union Territory of Delhi, Sikkim, northern parts of Uttar Pradesh, Bihar and West Bengal, parts of Gujarat, some parts of Maharashtra near the west coast and Rajasthan.
Moderate risk Zone-III includes Kerala, Goa, Lakshadweep islands, the remaining parts of Uttar Pradesh, Gujarat and West Bengal, parts of Punjab, Rajasthan, Madhya Pradesh, Bihar, Jharkhand, Chhattisgarh, Maharashtra, Orissa, Andhra Pradesh, Tamil Nadu and Karnataka.
The rest of the country is Zone-II.
Almost 59 per cent of India is prone to earthquakes of different magnitudes—11 per cent in Zone V, 18 per cent in Zone IV and 30 per cent in Zone III.
Buildings and earthquakes
Strange as it may sound, earthquakes do not kill, it is the structurally unsound buildings that do. Experts say earthquakes are a hazard that need not get converted into a disaster if buildings are safe, everyone follows the law and there is a -drafted disaster management plan in place.
While India has National Building Code and stringent rules and regulations related to constructing safer buildings, the question is the implementation.
India has well developed BIS and earthquake resistant guidelines. The 1962 guidelines were revised in 2002 after the devastating Bhuj earthquake resulting in devastation and death toll (anywhere between 13,805 and 20,023) of unimaginable order.
They deal with earthquake-resistant construction—design, construction, improving earthquake resistance, repair and seismic strengthening of buildings etc.
Contrary to popular belief, a structurally sound high-rise is safer than an unscientifically constructed single-storied house.
During an earthquake, a building experiences transverse and longitudinal vibrations.
As the ground moves randomly, the top weight vibrates accordingly.
Any building constructed under the supervision of structural engineers with attention to material grades and designs to ensure its movement as a single unit in the event of an earthquake will be able to sustain the impact due to uniformity of structure.
While new buildings can be made safe by following the laws, structural stability of old ones can also be with the help of retrofitting, etc.
However, the problem is most Indian cities have been urbanised in the most haphazard and unorganised way and buildings constructed in clear defiance of laws.
