In a way to understand the seismic response of underground structures, researchers mostly define the maximum thrust or maximum bending moment against PGA (Peak Ground Acceleration) as intensity measure. But, there are other ground motion parameters like PGD (Peak Ground Displacement), PGV (Peak Ground Displacement) or any tectonic characteristics (i.e. fault length; source to site distance, focal depth, fault or thrust type) etc.
Why PGA is most dominating measuring factor among all, so as to represent the earthquake induced intensity?
PGA is a parameter that could represent the earthquake damage level. For example PGA could be correlated to damage intensity level such as MMI (modified mercalli intensity). In addition, PGA is the maximum peak ground acceleration for time-history. Spectral Acceleration is main factor for structural analysis in structural design and it is derived from time history of acceleration. So that for analysis of structure and damage intensity level could be represented by acceleration and the maximum acceleration is PGA.
The acceleration Parameter is directly related to force. So, in soil-structure interaction, PGA is used. We can easily find the amount of force that will be exerted on structures.
Because PGA relates directly to shaking hazard, i.e. damage potential. PGV (Peak Ground Velocity) is also used, but not as meaningful: change in velocity is a better indicator than velocity itself.
That is come from point of interest.
Seismic resisting of structure is the target of objective (Passive or line of defend view). Not to study source of energy.
PGA ( rate of change V) is directely effect on f=ma ( it is inertia of mass). estimated a ( where at selected site) is relative to other factors (Mw/fault..distance.. Fault type.. Transfer media.. ). complex evaluation by geotechanical engineer.
Generally..
the evaluation of a is depend upon the site sisturation ( not directely connect to Source energy.. but so relative).
It is better to apply with simplify method without consideration of anymore geothechanical and seismic detail study ( Structural engineer.).
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