CDS (II) 2021 General Knowledge · Question 83 of 120

Correct — C, Malti at Pithoragarh. Of the four places named, only Pithoragarh sits on the Himalayan front, where the Indian plate is being driven under Eurasia along a stack of thrusts and where the country's largest earthquakes occur; Uttarakhand government disaster-management material places the district in Zone V, the highest category on the Indian zoning map. The other three lie in the stable peninsular interior, and the code's own town list settles two of them outright: Hyderabad, of which Secunderabad is the twin city, is in Zone II with a zone factor of 0.10, the lowest category there is, and Bhubaneswar is in Zone III with a factor of 0.16. Indore is not separately listed, but Madhya Pradesh's listed towns sit in Zones II and III as well. So the ranking is unambiguous even before the exact zone number for Pithoragarh is settled.

• (a)Shahji at Secunderabad — Secunderabad is the twin city of Hyderabad, which the Indian seismic code places in Zone II with a zone factor of 0.10 — the lowest hazard category in the country.
• (b)Ranbir at Indore — Indore lies on the Malwa plateau in the stable peninsular interior. Madhya Pradesh's listed towns fall in Zones II and III, well below the Himalayan front.
• (d)Maitri at Bhubaneswar — Bhubaneswar is placed in Zone III with a zone factor of 0.16 — moderate hazard, and two full categories below the Himalayan districts.

India's seismic zoning map divides the country into four zones, II to V, with zone factors of 0.10, 0.16, 0.24 and 0.36 and expected maximum intensities of about VI, VII, VIII and IX or more on the Medvedev-Sponheuer-Karnik scale. The hazard is not spread evenly, and the reason is tectonic: the Indian plate converges on Eurasia at roughly five centimetres a year, and that convergence is taken up along the Himalayan Frontal Thrust, the Main Boundary Thrust and the Main Central Thrust, all of which sole into a single detachment at depth. Zone V therefore follows the mountain arc — the Kashmir valley, the western and central Himalaya, north Bihar and the whole North-East — with two outliers, the Rann of Kutch and the Andaman and Nicobar Islands.

Scenario questions of this shape reduce to a map exercise: identify which of the four names is on an active plate boundary. Two honest qualifications belong on this card. First, the stem credits the Geological Survey of India with specifying the hazard zones; the zoning map that engineers actually use is a Bureau of Indian Standards product published with the earthquake-resistant design code, while the Survey contributes the seismotectonic mapping behind it, so the attribution in the stem is loose. Second, the code's own town list does not include Pithoragarh, and neighbouring Kumaon towns such as Almora and Nainital appear in Zone IV; the answer does not depend on resolving that, because even Zone IV would outrank Zone II and Zone III by a wide margin.

• India's zoning map has four seismic zones, II to V, with zone factors of 0.10, 0.16, 0.24 and 0.36 respectively.
• Zone V follows the Himalayan arc and also covers the Rann of Kutch and the Andaman and Nicobar Islands.
• Hyderabad, of which Secunderabad is the twin city, is listed in Zone II; Bhubaneswar is listed in Zone III.
• Uttarakhand government disaster-management material places Pithoragarh district in Zone V.
• The Himalayan hazard arises from convergence of the Indian and Eurasian plates at roughly five centimetres a year, taken up on the Himalayan Frontal, Main Boundary and Main Central Thrusts.

• Assuming a large or well-known city must face greater hazard; Hyderabad is in the lowest zone.
• Confusing intensity, which describes effects at a place, with magnitude, which describes energy released at the source.
• Forgetting the two non-Himalayan parts of Zone V, the Rann of Kutch and the Andaman and Nicobar Islands.

As a which-place-is-most-at-risk item, as a zone-to-region match, or as a statements question on magnitude and intensity scales.

• practice — not a real PYQ

  Which one of the following areas lies in the highest seismic zone of India despite being far from the Himalaya?

  • (a)Rann of Kutch
  • (b)Malwa plateau
  • (c)Chhotanagpur plateau
  • (d)Coastal Andhra Pradesh

  Answer(a) Rann of Kutch — it lies in Zone V, and the Bhuj earthquake of 2001 is the reminder of why.

• practice — not a real PYQ

  The intensity of an earthquake, as distinct from its magnitude, is described on which one of the following scales?

  • (a)Richter scale
  • (b)Modified Mercalli scale
  • (c)Moment magnitude scale
  • (d)Beaufort scale

  Answer(b) Modified Mercalli scale — intensity records effects at a place, while magnitude measures energy released at the source.