Peak Ground Acceleration

Mechanism of amplification due to soft surface layer

Level of damage done to a structure depends upon:

  • Acceleration at a site.
  • Duration of shaking (increases with size of the earthquake)
  • Type of ground (shaking in soil is larger than in hard rock)

Acceleration is given as percentage of the acceleration of gravity (g).

Acceleration is first estimated at a site at bed rock level by

  • Probabilistic method
  • Deterministic method

  • Probabilistic method : Peak ground Acceleration (PGA) is estimated for 50yr return period at 2% and 10% probability in Gujarat taking into account the past seismicity.

  • Deterministic estimate of acceleration is estimated for fault in the region for example due to West Cambay fault in Dholera SIR
  • Amplification due to soil layer is estimated by actual earthquake recordings, geophysical methods of seismic velocity measurements & soil investigations in boreholes

  • Shaking due to an earthquake causes liquefaction that makes the soil loose its strength. Water and sand oozes out, sometimes as fountains.

Peak Ground Acceleration


  • ISR has started geophysical surveys for Geothermal Energy in Gujarat state. ISR has pioneered a technique of 3D MT imaging of crust. Geological faults and crustal structure have been mapped in Kachchh.
  • ISR is carrying out Multiparametric Geophysical and Geochemical studies in Kachchh for earthquake prediction research.
  • ISR has upgraded Gujarat State Seismic Network from 19 online seismic stations to 40.