Expert/source verification requiredEdition-dependent or normative details must be confirmed against the adopted standard and National Annex before project use.
Ground motionPGAReference seismic actionProbability and return period
Learning objectives
In this lesson
- PGA is not a complete description of demand.
- Probability communicates risk, not event timing.
Engineering explanation
Earthquake motion varies in amplitude, frequency content and duration. PGA describes only part of that motion and must be interpreted with the governing spectrum, ground conditions and importance context. Return-period language is a statistical representation of hazard, not a prediction of the next earthquake. The project team must obtain reference action and Nationally Determined Parameters from the applicable official hazard source and National Annex; remembered or neighbouring-country values are not acceptable substitutes.
Key takeaways
What to carry forward
- PGA is not a complete description of demand.
- Probability communicates risk, not event timing.
- Hazard inputs require authoritative sources.