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.