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‘Delhi’s position and earthquake zones of India’

  • Category
    Geography
  • Published
    29th Dec, 2020

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.

Context

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.

Background

  • 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.

Know Your Basics                                                             

What are tectonic plates?

The Earth’s lithosphere, which includes the crust and upper mantle, is made up of a series of pieces, or tectonic plates, that move slowly over time. There are three main types of plate boundaries:

1. Convergent boundaries: where two plates are colliding

  •  Convergent plate boundaries are locations where lithospheric plates are moving towards one another.
  • One plate eventually slides beneath the other, a process known as subduction.
  • Subduction zones occur when one or both of the tectonic plates are composed of oceanic crust. The denser plate is subducted underneath the less dense plate. The plate being forced under is eventually melted and destroyed.

       i. Where oceanic crust meets ocean crust

  • Island arcs and oceanic trenches occur when both of the plates are made of oceanic crust. Zones of active seafloor spreading can also occur behind the island arc, known as back-arc basins. These are often associated with submarine volcanoes.

      ii. Where oceanic crust meets continental crust

  • The denser oceanic plate is subducted, often forming a mountain range on the continent. The Andes is an example of this type of collision.

     iii. Where continental crust meets continental crust

  • Both continental crusts are too light to subduct so a continent-continent collision occurs, creating especially large mountain ranges. The most spectacular example of this is the Himalayas.

2. Divergent boundaries: where two plates are moving apart

  • The space created can also fill with new crustal material sourced from molten magma that forms below. Divergent boundaries can form within continents but will eventually open up and become ocean basins.

       i. On land: Divergent boundaries within continents initially produce rifts, which produce rift valleys.

      ii. Under the sea: The most active divergent plate boundaries are between oceanic plates and are often called mid-oceanic ridges.

3. Transform boundaries: where plates slide passed each other

  •  The relative motion of the plates is horizontal. They can occur underwater or on land, and crust is neither destroyed nor created.
  • Because of friction, the plates cannot simply glide past each other. Rather, stress builds up in both plates and when it exceeds the threshold of the rocks, the energy is released – causing earthquakes.

Analysis

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.

Indo-Australian Plate

  • The Indo-Australian Plate is one of Earth’s 7 major plate tectonic boundaries. It’s the second smallest being slightly larger than the South American Plate.
  • At about 58,900,000 km2, the Indo-Australia plate is the sixth largest plate tectonic boundary.
  • The Indo-Australian Plate includes the majority of the Indian Ocean. It borders:
    • the Eurasian Plate in the north
    • the Antarctic Plate in the south
    • the Pacific Plate in the east

What causes Earthquake?

  • 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.

Seismic Zones in India

  • 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.

Major Indian cities and their earthquake zones

  • Zone V cities– Guwahati and Srinagar
  • Zone IV cities — Delhi, Patna, Dehradun, Jamnagar, Meerut, Jammu, Amritsar and Jalandhar
  • Zone III cities — Ahmedabad, Vadodara, Surat, Rajkot, Bhavnagar, Pune, Bhiwandi, Nashik, Greater Mumbai, Thane, Bhubaneswar, Cuttack, Chennai, Asansol, Coimbatore, Agra, Varanasi, Bareilly, Lucknow, Kanpur, Kolkata, Indore, Jabalpur, Vijaywada, Dhanbad, Mangalore, Kochi, Kozhikode, Trivandrum.

What is Delhi’s geographic location?

  • 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.

Conclusion

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.

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