Page 57 - 15MAY2019E

calamity

Himalayas region as predicted by a recent The Himalayan fault is known to have a Public involvement
study, the National Capital Region (NCR) potential to generate earthquakes up to a However, to ensure preparedness, the
of Delhi would suffer very heavy damage. magnitude of 8 or more. The foundations public needs to be involved in question-
The 2001 earthquake in Bhuj in Gujarat, in Delhi are not on solid rock but there ing whether their buildings are safe. Par-
which claimed about 10,000 lives, had is excess of soil and crushed rock (mur- ticipants at the workshop, as per a news
shown that the destruction by an earth- rum) on the ground. In case of a powerful agency report, also raised questions on
quake is caused by two different types of earthquake in the Himalayas, the long scis- how socio-economically weaker sections
waves: Shear Waves, confined to about 70 sors of Rayleigh Waves could wildly chop would invest in building earthquake re-
to 100 km from the epicentre and which the tall concrete structures in Delhi and sistant buildings. Dr Durgesh C Rai from
adversely affect the foundations and base- neighbouring areas. The possibility that IIT Kanpur said it is the right of every in-
ments of structures; and Rayleigh Waves these buildings may collapse like a pack of dividual to have seismic safety, and the
that travel with a velocity between 2.5 to cards in “Ahmedabad Fashion” cannot be government has to ensure that. “Seismic
3 km per second and produce a different ruled out. safety should not be an optional require-
type of destructive effect. Fluctuations in the Earth’s rotation are ment,” he said.
These Rayleigh Waves from earth- tiny - changing the length of the day by While presenting his research, Rai
quakes of magnitude above 7.5 become several milliseconds - but could be enough focused on how publicly-funded govern-
active at a distance beyond 150 to 200 km to release vast amounts of underground ment buildings in Himalayan states such
or more from the epicentre and adversely as Sikkim and Manipur could not survive
affect tall structures (height more than 17 even low intensity earthquakes. Accord-
meters) as was observed at Ahmedabad Numerous research ing to him, we continue to repeat the
city located at a distance of about 320 same mistakes time and again, and have
km from the Bhuj earthquake’s epicen- groups, including not learnt any lessons from the failures
tre. Another very important observation one at IIT Roorkee, of the past. Giving the example of the 1993
was that all structures with “stilted” floors earthquake that struck Latur, Maharash-
(where the ground floor is used for vehicle are developing early tra — killing over 9,000 people — Rai said
parking) were severely damaged. A similar earthquake warning government agencies and academicians
damaging effect by Rayleigh waves was were of the view that buildings which
observed in Mexico City, located about systems which may give collapsed were non-engineered. “So the
500 km from the epicentre of the 1985 people up to a minute deaths of people were linked to their pov-
earthquake. erty,” he added.
The Himalayan states had been visited of warning before the “In 2001, the Bhuj earthquake — 120
by a number of large magnitude earth- multi-storey buildings collapsed in
quakes and a recent study suggests the NW quake. But short-term Ahmedabad — killed over 900. This was
region (mostly Uttarakhand, Himachal predictions are not the engineered construction. The investiga-
Pradesh and parts of Kashmir) is ripe for tions showed that every building code
one. The Delhi NCR escaped major damage best way forward was flouted,” Rai said. “Earthquakes need
from the destructive Rayleigh Waves from not be deadly or destructive if we use the
past earthquakes because, prior to 1950, energy, they have said. It has been reported right designs and materials.” He added that
there were no high rise buildings there. that on five occasions in the past century, a seismic safety should not be an optional
But the situation is now different. 25-30 per cent increase in annual number feature that people have to ask for. Rather,
With its satellite townships of Noida, of earthquakes (of magnitude 7 or greater) all buildings should be built to be earth-
Greater Noida, Gurugram, Ghaziabad and coincided with a slowing in the mean quake safe by default — much like medi-
Faridabad, NCR Delhi forms a big cluster of rotation velocity of the Earth. The slow- cal instruments are sterilised before use,
high-rise buildings with flyovers, bridges ing down of Length of Day (LoD) normally irrespective of whether a patient is rich
and elevated roads. It is also known that lasts for six years, after which the earth or poor. He pointed out that many older
some of the high-rise structures have enters a period of enhanced seismicity. In buildings in the Himalayan arc have sur-
collapsed during construction itself. this century, the LoD started in 2011 and vived earthquakes for decades, and these
Many high-rise buildings have stilted now the year 2018 could be considered a could serve as lessons for our future. “Loss
floors. As was witnessed in Ahmedabad period of higher seismic activity. While of life occurs due to building collapse and
after the Bhuj earthquake, all these struc- the research did not indicate precisely damage, we need to engineer structures
tures could suffer heavy damage in case when and where these future earth- with proper building codes,” said Ramesh
of a large magnitude earthquake in the quakes will occur, it showed that most of P Singh, coordinator of the workshop, and
NW Himalayan region with its epicentre the intense earthquakes that responded visiting professor at IIT Mandi.
in the range of 270 to 350 km from NCR to changes in day length seemed to occur
Delhi. near the equator. letters@tehelka.com

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