Why do Nepal quakes shake north India? Delhi NCR buildings under threat?

Nepal has grappled with a series of devastating earthquakes over the past decade. It all began with the 7.8 magnitude quake in 2015, and since then, Nepal has experienced frequent tumblers that often reverberate across Northern India.

The most recent earthquake struck the Himalayan nation on November 3, registering a magnitude of 5.6, coming just two days after a 4.0 magnitude one. These seismic activities also sent shockwaves across Northern India.

Why is this happening?

Renowned geologist Dr CP Rajendran, an adjunct Professor at the National Institute of Advanced Studies in Bengaluru, said that since the 2015 earthquake, the Himalayan region has been under immense pressure. "This pressure results from the interaction of two tectonic plates: the Indian plate and the Eurasian plate."

The two plates are constantly pushing against each other and over time, stress accumulates and periodically releases as earthquakes, as was the case with the recent Nepal earthquake, he told WION.

However, this stress accumulation varies across the Himalayan region, with each area having its unique characteristics. In some regions, stress accumulates to such an extent that when released in the form of an earthquake, it places stress on the other part.

Due to the ongoing tectonic activity in Nepal since 2015, the entire region has become increasingly unstable. Furthermore, certain areas experience compounded stress due to past earthquakes.

Also watch | Another 5.6 magnitude in Nepal jolts the Himalayan nation

Are high-rise buildings in Delhi NCR under threat?

The repercussions of these Himalayan earthquakes are felt in the Gangetic alluvial plains, including areas like Delhi NCR, Lucknow, Patna, Kanpur, and Varanasi. The seismic waves travel southward from the Himalayas towards this belt.

"If you drill the ground, you will see a huge pile-up of sediments transported by rivers. So, when the energy released through an earthquake is propagated towards the south, which also forms the Delhi NCR area, it gets amplified because these places are sitting on soft sediments," notes Dr Rajendran.

As a result, residents in Delhi NCR often experience more pronounced shaking, with this effect significantly magnified in high-rise buildings. 

Dr Rajendran said that in the realm of earthquake literature, a common saying is "Earthquakes don't kill, but buildings do."

The primary source of damage is buildings, particularly in urban areas. Those residing in forested or open regions face fewer risks. The real danger emerges when people are within structures that might collapse. 

To mitigate the impact of earthquakes, it's essential to construct buildings that can "effectively withstand tremors" and seismic activities, he adds.

Also read | Explained | Four earthquakes in over 30 days: Why is Delhi experiencing tremors so often?