‘Delhi’s position and earthquake zones of India’

Whenever earthquake hits Delhi, there starts discussion on the tectonic faults that the city lies on. In this regard, it is essential to understand the major earthquake zone where does the national capital stand.

• The terrain of Delhi is flat in general except for the north-northeast (NNE)-south-southwest (SSW) trending ridge.
• The region is considered as an extension of the Aravalli hill, which is buried under the Yamuna alluvium in the northern parts of Delhi.
• River Yamuna enters the city and forms a tri-junction with the Lahore-Delhi ridge, and the Delhi-Haridwar Ridge.
• This region is seismically active and shows sporadic activity aligned in NNE-SSW direction, nearly perpendicular to the Himalayan arc. 
• Apart from local tectonic faults, the proximity of the Himalayan region makes Delhi susceptible to the earthquakes from Himalayan seismic sources.
• Thus, the region around Delhi is inhomogeneous as far as its seismotectonic status is concerned.

Where does India lie?

• India lies at the north-western end of the Indo-Australian Plate, which encompasses India, Australia, a major portion of the Indian Ocean and other smaller countries. 
• Indo-Australian Plate is colliding against the huge Eurasian Plate and going under the Eurasian Plate.
• This process of one tectonic plate getting under another is called subduction.

• The primary cause for an earthquake is the movement of rocks beneath the earth’s surface.
• The movement is usually caused by the continuous movement of plates that make up Earth’s crust.
• This movement exerts stress on rocks, causing the latter to respond by breaking along existing fractures called fault lines.
• The sudden release of energy during such breakup causes the tremors.

• While scientists cannot predict the time, place, or the exact scale of these quakes, consistent seismic activity around the Delhi-NCR region could be a precursor to a major earthquake.
• There are a total of four seismic zones in India.
  • Zone V: Entire northeastern India, parts of Jammu and Kashmir and Himachal Pradesh, Uttaranchal, Rann of Kutch in Gujarat, parts of North Bihar and Andaman & Nicobar Islands.
  • Zone-IV:The remaining parts of Jammu and Kashmir and Himachal Pradesh. Delhi-NCR region, Sikkim, northern parts of Uttar Pradesh, Bihar and West Bengal, parts of Gujarat and small portions of Maharashtra near the west coast and Rajasthan.
  • Zone III:Goa, Kerala, Lakshadweep, remaining parts of Uttar Pradesh, Gujarat and West Bengal, parts of Punjab, Rajasthan, Madhya Pradesh, Bihar, Jharkhand, Chhattisgarh, Maharashtra, Orissa, Andhra Pradesh, Tamil Nadu and Karnataka.
  • Zone II: Parts that are not under the above zones.

• Delhi is vulnerable to earthquakes in particular mainly because of its location. Delhi is situated on top of few active seismic fault lines. Moreover, its proximity to other active seismic fault lines further worsens the situation.
• Delhi falls under the fourth-highest seismic zone, which makes it vulnerable to earthquakes.
• Furthermore, it lies in the Himalayan foothills.
• Since the formation of the Himalayas, a large part of the crust under the mountain ranges has remained deformed.
• These rocks remain stressed and folded due to the continuous movement of the Indian plates under the mountain.
• And when the piled-up stress gets released, it produces minor frequency earthquakes in and around the National Capital Region.

The entire Himalayan seismic zone is vulnerable to strong earthquakes. The Indian tectonic plate is continuously driving into the Eurasian plates around this region at a speed of 44 mm/year. Due to this motion of tectonic plates, stress builds up, and the earthquakes are triggered to release tension. Not only Delhi, but many parts of north, east and northeastern India are at constant risk of strong earthquakes due to this phenomenon.