Clause 6.4.2 divides India into four seismic zones (II, III, IV, V) based on the expected intensity of earthquake ground motion. The zone factor Z is the peak ground acceleration (PGA) as a fraction of g for the Maximum Considered Earthquake (MCE). The design basis earthquake (DBE) is taken as half of MCE, hence Ah uses Z/2. Zone I from earlier editions has been merged into Zone II.
Key Requirements
•India is divided into 4 seismic zones: II, III, IV and V
•Zone factor Z represents peak ground acceleration for MCE as a fraction of g
•Zone factor shall be obtained from Table 3 or Annex A (zone map, Fig. 1)
•For sites near the boundary of two zones, the higher zone factor shall be used
•Former Zone I has been merged with Zone II in the 2002 and subsequent revisions
Reference Tables
Table 3 — Zone Factor Z (Clause 6.4.2)
Seismic Zone
Zone Factor Z
II (Low Intensity)
0.1
III (Moderate Intensity)
0.16
IV (Severe Intensity)
0.24
V (Very Severe Intensity)
0.36
Z is the zero period acceleration value for MCE. For DBE, the factor is Z/2.
Practical Notes
✓Most of peninsular India falls in Zone II or III; the Himalayan belt, Kutch, and North-East India are in Zone IV or V
✓Always verify the zone from the IS 1893 Annex A map or the city list in Table 2 — municipal boundaries can straddle zones
✓For important projects near zone boundaries, a site-specific seismic hazard study is recommended
Common Mistakes
⚠Using Z directly instead of Z/2 in the Ah formula — Z is for MCE, design uses DBE = MCE/2
⚠Referencing the old 5-zone classification (Zone I no longer exists)
⚠Failing to check the zone for the exact project location — some cities span two zones