NEW DELHI: Close to the city, which lies mainly in the high-risk seismic zone 4, are several fault lines – Aravali, Mahendragarh-Dehradun, Haridwar Ridge, Mathura and Sohana. Monday morning’s tremor, however, had its origin in a partially dried lake in southwest Delhi’s Dhaula Kuan.
The tremor measuring 4 magnitude was the strongest in five years since May 29, 2020, when one of 4.5 magnitude originated in the same area. Given Delhi’s dense population and its proximity of 250km from the Himalayas – the highest risk seismic zone 5 – talks about the city’s earthquake preparedness dominated the conversations on Monday.
Specialists noted that whilst the region had multiple fault lines – vulnerable areas where tectonic plates meet and cause seismic activities – the primary threat came from the Himalayan region, but the capital was vulnerable due to its crowded urban spaces and substandard constructions.
“Delhi-NCR seismic activity is not very high. The faults in the Himalayan region are the main active ones. This is the reason why Delhi experiences light tremors that originate within the city but gets shaken up by even moderate tremors in the Himalayan region,” explained JL Gautam, senior scientist at the National Centre for Seismology (NCS), reminding that there is no technology capable of forecasting the time, space and magnitude of earthquakes.
Gautam said that while Delhi was unlikely to experience Himalayan-level quakes due to geographical differences, such a possibility couldn’t be discounted entirely. “A Himalayan earthquake might set off strong tremors in Delhi, but not as strong as those in Nepal or Tibet. Monday’s earthquake had a high impact because of the shallow depth and proximity of the epicentre,” he said. In the Himalayan region, there is subduction or collision zones caused by the collision of two plates-Indian and Eurasian. Since Delhi lacks these zones owing to the involvement of only one Indian plate, the depth and area of impact in Delhi will be lesser, said Gautam.
Monday’s incident highlighted the limited research attention given to the Aravali-Delhi Fold Belt which impacts the city. NCS head OP Mishra noted that his organisation was currently researching various fault lines and weak zones, among which was Monday’s quake location. He, however, said the city’s residential buildings appeared to be capable of withstanding tremors. “Delhi regularly suffers micro quakes, sub-shallow and low-magnitude quakes occurring at sub-shallow or shallow depths,” Mishra pointed out. “Delhi also survived the tremors resulting from major Himalayan quakes like those that devastated Chamoli and Nepal. This means that buildings are risk- resilient. He added, however, that vigilance was still required and factors such as how quickly children, women and elders could be evacuated from tightly packed regions had to be considered.
Mishra also revealed that while additional research on Aravali, Doon and Delhi Haridwar Ridge faults was needed, numerous studies were in progress. “We are already assessing the potential seismological threats with reference to the existing faults,” he claimed. “Besides, we are also assessing structural and material heterogeneity of the region that caused Monday’s quake. In 2023, we published a report on the electrical characterisation of the Delhi-NCR with reference to conductivity, deciphering the presence of water and gas, which lead to ruptures of base stones and cause quakes like the one on Monday.” The NCS director recalled that the areas between the Yamuna and Ridge fell in both zones 3 and 4 and in 2016, NCS had submitted a micro-assessment of the city based on risks involved for all stakeholders to take apt measures.
