Explainer: Why does Delhi NCR frequently experience earthquakes, what causes seismic activity in region?

Today, Delhi NCR including Delhi, Noida, Gurugram and parts of Lucknow and Uttarakhand experienced two earthquake tremors, measuring 4.6 and 6.2 in magnitude, at a depth of 5 km. While seismic activity is not uncommon in this region, occurring approximately every 3-4 months, many wonder why Delhi NCR witnesses frequent earthquakes.

Earthquakes are caused by the movement of tectonic plates beneath the Earth's crust. These plates which are situated deep within the Earth's uppermost layer, the crust, interact with each other. When two blocks of the Earth's surface move against each other, it triggers seismic activity.

The origin point of an earthquake is called the 'focus,' situated inside the Earth's crust. The point on the surface directly above the focus is termed the 'epicenter.' When energy is released at the focus, seismic waves radiate outward in all directions.

India's northern region hosts the Himalayas, the newest mountains on Earth. The Indian plate's movement towards the Nepalese plate formed the Himalayas. The Himalayan region, spanning North India to Northeast India, frequently experiences earthquakes due to its location on the boundary (fault zones) of two massive tectonic plates. The collision of these plates renders both India and Nepal susceptible to seismic activity.

Approximately 59% of India's total landmass, encompassing all states, is prone to earthquakes of varying intensities, according to the Indian government. The seismic zoning map classifies the country into four seismic zones. Zone V is the most active, while Zone II is the least. Zone-5, with the highest earthquake risk, includes eight states and Union Territories. The Delhi-NCR region falls into Zone IV.

Percentage of India’s total landmass area in Earthquake Seismic Zone:

Zone V: 11% (most active)

Zone IV: 18%

Zone III: 30%

Zone II: 41% (least active)

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