Sept. 20: Mangan town, which many consider the epicentre of the quake, does not show extensive damage and only one death has been reported there so far.

The relatively unscathed appearance of Mangan has revived suggestions that epicentres of quakes are safe-haven oases that escape the brunt of the fury.

However, seismologists and earthquake engineers have cautioned that the strongest ground movements should be expected at the epicentre of the earthquake, quite unlike an atmospheric cyclone where the eye of the storm is calm relative to the high-speed winds around it.

The damage to buildings and other structures during an earthquake depends not just on their distance from the epicentre but also on the type of ground they stand on and the design and quality of construction, the earthquake engineers added.

Mangan town cannot be conclusively termed the epicentre, either. According to data available so far, the town falls within 50km of the epicentre of Sunday’s first — and the day’s biggest — earthquake of 6.8 magnitude. Seismologists have concluded that the epicentre of the 6.8 event was somewhere beneath the Kanchenjungha mountain, not Mangan.

But there is disagreement among seismologists over the location of epicentres of two subsequent events — 5.3 and 4.6 — both east of the primary shock.

Scientists from the Indian Institute of Science Engineering and Research, Calcutta, hope to pinpoint the epicentres after studying data on instruments at three sites — Yumthang, 20km north of Mangan, Rabangla, 15km south of Mangan, and Pangthang, 5km west of Gangtok.

“These instruments are closest to the events — we’re waiting for the data,” said Shyam Sunder Rai, a geophysicist at the National Geophysical Research Institute, Hyderabad.

Army personnel on a rescue mission at Pegong in North Sikkim. Congress MP Rahul Gandhi is expected to land in Bagdogra on Wednesday and take a helicopter to Chungthang, about 5km away, which till Tuesday was cut off for rescuers. Picture taken by Prabin Khaling aboard an IAF chopper

The lone death on the outskirts of Mangan town took place when a church collapsed on Nirmala Tamang, the 27-year-old wife of a pastor. The buildings in the town are intact with minor cracks here and there.

“People here are religious and resilient. They have not panicked,” North Sikkim district collector S.K. Pradhan said.

Entrepreneur Sonam Paljor added: “People are doing their normal duties. We are more worried about the road and power. We need to charge our mobile phones so we can call our near and dear ones.”

A lady running a restaurant in Mangan said: “We were serving food to our customers at our restaurant when the quake took place. Immediately, all the people rushed out into the streets. The lights also went off.”

“Almost everyone in the town spent Sunday night in the school playground and other open spaces. The number of people staying out in the night has come down though some people are spending the night in trucks and vehicles,” the restaurant owner in Mangan said.

The lady said she did not close her restaurant and resumed normal business the next day.

A seismologist explained how local effects play a role in the devastation that follows a quake. “The earthquake energy always weakens with distance from the epicentre — if we discount local effects,” said Hans Raj Wason, a seismologist and head of the earthquake engineering department at the Indian Institute of Technology, Roorkee.

Local effects can dramatically amplify waves, depending on the type of ground where structures are located. Buildings standing on hard bedrock are relatively safer than those built on soft ground such as alluvial soils, he said.

An 8.1-magnitude temblor that shook Mexico in 1985 provides a classic example of destruction from amplification, Wason said. The epicentre was about 370km from Mexico City but over 200 buildings collapsed in the city. Scientists determined that many of these buildings were located on a reclaimed lakebed where layers of soft soil and clay amplified the ground-shaking 8-50 times relative to shaking over hard rock, he said.

But poor design and construction are also likely to have contributed to the damage elsewhere, according to structural engineers.

“I’ve seen some scary buildings — in Gangtok and in other places,” said Sudhir Jain, a civil engineer and director of the Indian Institute of Technology, Gandhinagar, who has long been arguing for strict enforcement of building codes by state authorities across the country.

“The Gujarat earthquake in 2001 was a wake-up call — India made the earthquake safety codes in buildings mandatory after that,” Jain told The Telegraph. “But they need to be enforced uniformly across the country — we don’t think this is happening.”

The codes specify rules for the design of structures as well as construction material to be used to ensure that buildings do not crumble when they experience strong ground motion.

“The philosophy is: no loss of life despite damage to buildings,” said Shailesh Agarwal, director of the Building Materials and Technology Promotion Council, a government agency involved in earthquake-proofing efforts.

Structural engineers say poor design and construction had led to the collapse of several buildings in Ahmedabad during the 2001 Gujarat earthquake although there may have been some local site amplification.