Spatial variation of maximum considered and design basis earthquakes in peninsular India

Realistic seismic hazard assessment is essential for carrying out safe and economic design of structures. The zone factors corresponding to seismic hazard in different parts of India that has been specified in the IS code (IS 1893: 2002) does not fully consider the recent advances in understanding of seismic hazard in peninsular India. The recent damaging earthquakes in this region have indicated that the seismic zonation may not be accurate. The MCE-level peak horizontal accelerations may also be underestimated, considering the damage caused by moderate to large earthquakes in the past. The IS code also assumes a uniform ratio of maximum considered earthquake (NICE) to design basis earthquake (DBE) as 2, which may result in nonuniform margin of safety at NICE level ground motions. These issues have been discussed in this article based on probabilistic seismic hazard assessment of peninsular India. It is shown that uniform level of safety against NICE cannot be achieved in both peninsular India as well as the seismically active regions. It is also shown that the MCE-level ground motion earthquake is significantly underestimated in large parts of peninsular India