Seismic Zoning of India Questions and Answers

Answer: A

IS 1893 is the criteria for earthquake resistant design of structures, and Part 1 of it carries the zone map and the zone factors. IS 456 covers plain and reinforced concrete, IS 800 steel, and IS 875 the other loads such as dead, imposed and wind.

Answer: B

Correct answer: four

IS 1893 divides the country into four seismic zones, numbered II to V. The map has not always had four: the 1962 version had seven, and successive revisions consolidated them.

The last such change came in 2002, when Zone I was merged into Zone II after damaging earthquakes occurred in areas the map had placed in the lowest category. Fewer zones means each covers a wider range of expected shaking, which is a deliberate simplification - the map is a design tool rather than a scientific description of hazard.

Answer: C

Correct answer: II, III, IV and V

The numbering runs II to V in Roman numerals, and the gap at the start is historical rather than an oversight. Zone I existed in earlier versions and was merged into Zone II in the 2002 revision.

Retaining the original numbering avoided renumbering every zone on the map, in every code reference and in every district schedule, so a site described as Zone IV in 1984 remains Zone IV today. The severity rises with the number, Zone II being the lowest and Zone V the highest.

Answer: D

Correct answer: Zone V

Zone V is the highest hazard zone, carrying a zone factor of 0.36 - the largest value the code prescribes, and more than three times that of Zone II.

It covers the regions of greatest tectonic activity: the entire north-east, the Kutch region of Gujarat, the Andaman and Nicobar Islands, and parts of northern Bihar, Uttarakhand and Himachal Pradesh. Each of these has produced a great earthquake in the historical record, which is what the classification reflects.

Answer: A

Correct answer: Zone II

Zone II is the lowest zone in the current map, with a zone factor of 0.10. It is not Zone I, because Zone I no longer exists - it was merged into Zone II in the 2002 revision.

The merger followed the Killari earthquake of 1993, which killed some ten thousand people in an area then classified in the lowest zone. Zone II covers most of interior peninsular India. Note that a zone factor of 0.10 is not zero: buildings there still require earthquake-resistant design.

Answer: B

The 1993 Killari earthquake in Latur district struck ground the map then treated as the safest category, which made a lowest-hazard zone indefensible. The revision folded Zone I into Zone II so that a minimum level of design applies everywhere.

Answer: C

Correct answer: an area then classified as the lowest hazard zone

Killari lies in the stable peninsular shield, far from any plate boundary, and the pre-2002 map placed it in Zone I - the lowest category, where little was expected.

The earthquake killed around ten thousand people, in buildings designed on the assumption that shaking would be negligible. Together with the Jabalpur earthquake of 1997, also in central peninsular India, it showed that intraplate earthquakes can be damaging where none was anticipated, and it led directly to the abolition of Zone I in the 2002 revision.

Answer: D

The four factors run 0.10, 0.16, 0.24 and 0.36 for Zones II to V respectively. The value 0.36 represents the effective peak ground acceleration for the maximum considered earthquake, expressed as a fraction of gravity.

Answer: A

Correct answer: 0.24

The zone factors run 0.10, 0.16, 0.24 and 0.36 for Zones II to V, and Zone IV takes 0.24.

The value is the expected peak ground acceleration in units of \( g \) for the maximum considered earthquake. It enters the design coefficient as \( Z/2 \), the halving expressing the design basis earthquake as half the maximum considered event - so the effective acceleration used in design for Zone IV is 0.12g before the importance and response factors are applied.

Answer: B

Correct answer: 0.16

Zone III carries a zone factor of 0.16, the second lowest of the four.

It covers a wide band of the country, including Mumbai, Chennai, Kolkata, Kerala and Goa, so it is the zone most Indian urban construction is designed for. The four values - 0.10, 0.16, 0.24, 0.36 - are worth committing to memory as a set, since a great many design questions turn on nothing more than reading the right one and dividing it by two.