Luke, I've never heard of the rate of change of G having any significance - G itself is a rate of change (acceleration) and that is what affects the structure. I may not be up to speed on the physics of this but I cant see how the rate of change of a rate of change signifies anything in terms of physical effects on the system.
Totalising G over time is used to calculate fatigue life, sure, and that may be the case here but that's a simple matter of integrating the signal from the G meter...and is surely only useful as a long-term measure of things like spar life, not short sharp shocks?
Can you - or anyone else - explain whether this is the case? And also what that graph is for?