Major earthquakes can hit Himalayan region; Here’s why Delhi-NCR needs detailed seismic hazard map

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Published: June 10, 2020 5:18 PM

On Monday, there was a 2.1 magnitude earthquake, which was too mild to be according to the National Center for Seismology, and the epicentre was 13 km from Haryana’s Gurugram.

Major earthquakes in delhi, Himalayan region, delhi ncr earthquakes, reasons for multiple delhi ncr earthquake, Gurugram, seismic zone IV, latest news on earthquakeMost of the buildings in Delhi might not meet codal requirements on seismic resistance. (Representational image)

There have been so far 14 quakes of low and medium intensity which has been recorded in Delhi-NCR since April. The city of Delhi is located in seismic zone IV, the second-highest earthquake hazard zone in the country. On Monday, there was a 2.1 magnitude earthquake, which was too mild to be according to the National Center for Seismology, and the epicentre was 13 km from Haryana’s Gurugram.

These mild tremors can be recorded only by seismographs. Though the earthquakes cannot be predicted like other natural disasters, according to seismologists, these tremors need to be monitored and that will help in being prepared.

What is causing these tremors?

According to reports, the Himalayan plate is moving in the north-northeast direction and it is subducting beneath the Eurasian plate. This has caused a lot of energy along the weak zones and these get released through fissures and lineaments.

There have been several small earthquakes in Delhi and Haryana and these have been in the last three years. What is of concern is that the shallow earthquakes which occur at a depth of few kilometres cause more damage than the more powerful ones.

Are we ready to deal with the disaster?

No.

Dr Angeli Qwatra, DG, Centre for Disaster Risk and Safety, New Delhi, shares her views with Financial Express Online. “Delhi region features a long seismic history being suffering from earthquakes of local origin also as those of Himalayan origin. This region is characterized by several dominant features such as the Delhi–Hardwar ridge, Delhi–Lahore ridge, the Aravalli–Delhi fold, the Sohna fault, the Mathura fault and the Moradabad fault. A study of more than 100 events recorded in the region has shown that the epicentres have a pattern of clustering in two belts, namely Rohtak and Delhi.”

According to Qwatra “Studies reveal that there is a possibility of a few major tremors in the Himalayan region which can severely affect Delhi-NCR.”

“The maximum size of an earthquake that may occur in this Delhi-NCR region would be 7.6. Experts predict that in a period of 50 years a magnitude 6 earthquake is almost certain and that there is a 80% probability of a 7 magnitude event visiting the region,” she says.

The level of safety of a city during an earthquake depends on a variety of factors including geology, topography, subsoil conditions, building morphology, communication network, and societal awareness.

“Seismic losses are greatly influenced by the earthquake resistance of buildings. The overwhelming majority of deaths and injuries in earthquakes occur because of the disintegration and collapse of buildings, and much of the economic loss and social disruption caused by earthquakes is also attributable to the failure of buildings and other human-made structures,” states DG, Centre for Disaster Risk and Safety. Studies of earthquake damage show that some sorts of construction tend to be more vulnerable than others.

“In order to predict the likely impact of an earthquake on the built environment in Delhi, it is essential to know the seismic the vulnerability of the built environment on the affected areas,” is her view. The city’s settlement pattern must be viewed in reference to the location and geological characteristics. In Delhi, Pockets with high rise buildings or ill-designed high- risk areas exist without specific consideration of earthquake resistance.

“The Central downtown namely Connaught Place, numerous District Centres and sprouting high rise group housing schemes are high-risk areas thanks to the vertical also as plan configurations. The walled city area, the trans-Yamuna area, and scattered pockets of unplanned settlements also figure as high-risk zones thanks to their substandard structures and high densities,” Qwatra adds.

The use of disaster scenarios for effective disaster management planning is essential in urban areas due to the intense concentration of people, infrastructure and resources that may be affected by a damaging earthquake. This results in the disaster management plans being prepared without carrying out a rigorous risk assessment.

Rigorous quantification of seismic hazard in detail for the Delhi region has not been carried out so far. According to the Vulnerability Atlas of India (1997) — shaking intensity VIII almost 6.5% houses in Delhi have high damage risk, and 85.5% houses have moderate damage risk.

Most of the buildings in Delhi might not meet codal requirements on seismic resistance.

“Thus, instead of being satisfied with a broad macro-zoning concept of Delhi being in zone IV, it will be prudent to delineate the hazard and the resulting risk at the city level. This involves a multidisciplinary effort on the part of scientists and engineers to make a seismic hazard map on the size of city sectors or blocks. Such a map would discriminate between soft soil and hard rock sites and would incorporate the depth of the soil deposit as a parameter in hazard estimation. To understand the damages caused to buildings on a large scale due to foundation failure, regions of soil susceptible for compaction and liquefaction have to be identified. Further, building damage depends on the strength of the structure which successively may be a function of parameters like the materials used, design details, quality of construction and age.”

Disaster prevention involves engineering intervention in buildings and structures to form them strong enough to face up to the impact of natural hazard.

Many lifeline buildings of Delhi could be damaged when earthquakes strike, limiting the government’s ability to deliver critical services. There is no legal framework to require that all constructions in Delhi must implement seismic code provisions. Systematic studies are needed on the vulnerability of various sorts of constructions within the NCT of Delhi. There is an urgent to develop a rational seismic retrofitting policy, first for the government-owned buildings and later for the private constructions; Need for updating seismic code especially with regard to the construction of bridges, flyovers & metro projects.

One area of major concern is the lack of a professional environment to ensure safe construction; Enforcement of codes is closely connected with political will and quality of governance at the local city level, and much remains to be done towards this.

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