After Turkey, question for Delhi: How safe is the city in event of earthquake?

“It has been observed that, and this has been published in a number of papers, that particular area, Garhwal-Kumaon, has not had an earthquake in the past 700 to 800 years. That number might vary depending on researchers, but we can take it as at least 500 years. Many people say it is a long time considering the movement and collision rate of the plate boundary. The Indian (tectonic) plate is colliding with the Eurasian plate and we have plate boundary and Himalayas. With this movement, which continues, you have stresses accumulating. There must be a release of stress,” Rajendran said.

Delhi lies in seismic zone-IV going by seismic zonation map of the Bureau of Indian Standards. The country is classified into four seismic zones, zone-V being the most active seismically and zone-II being the least active.

“The problem with Delhi is that it is in the Gangetic plain and is built on alluvium. As energy passes through soft alluvium, it gets amplified. With Bhuj earthquake, buildings collapsed some distance away in Ahmedabad since it was located in the Sabarmati basin. If energy passes towards Delhi, there can be higher amplification and damage can be higher than what we anticipate,” Rajendran added.

“In my knowledge, an earthquake near Uttarkashi with a magnitude of around 7.6 in 1803 is the last one that has affected Delhi. We have reported in some papers that the Qutub Minar was partially damaged then. Even with a moderate earthquake of around 6.1 in Chamoli, Uttarakhand, in 1999, damage was reported in a few houses close to the Yamuna. That is evidence that even a moderate earthquake can affect Delhi if houses are situated on alluvium. The Himalayas are capable of generating earthquakes of magnitude more than 8,” she said.

The earthquake that brought buildings crumbling down in Turkey on Monday measured 7.8 on the Richter scale, followed by a second one around 7.5.

While modern buildings may be designed for the shaking expected, with older buildings there is a lack of preparedness, Rajendran said. “This is a constant process. The government needs to invest in educating people and checking which buildings are vulnerable, that is not happening. We need to take stock of old buildings and there needs to be policy decisions on what to do with them,” she added.

A senior official in the National Disaster Management Authority said a national mitigation programme on earthquakes is being drafted. The official said disaster mitigation and response begin with districts and states.

S K Nath, professor of geophysics at IIT Kharagpur, who works on seismology and disaster mitigation and management, who was also a member of the advisory and monitoring committee for the seismic microzonation of Delhi done by the National Centre for Seismology, Ministry of Earth Sciences, and released in 2016, pointed out that since the timing and magnitude of earthquakes cannot be predicted, it is important to urbanise in keeping with the bye-laws for buildings. Older dilapidated buildings will have to be rebuilt and others, including heritage structures, will have to be retrofitted, he said.

Nath pointed to the necessity of following the 2002 BIS standards for earthquake resistant design of structures. The Unified Building Bye-Laws for Delhi also mention the BIS standards for structural safety and earthquake protection.