Barbara, I did not have time to read the links on this thread...but, increasing the stress may make it less likely that a fault in one orientation with one kind of slip will fail (will delay failure), while the same stress change will advance the time of rupture for another type of fault.
So...what accelerations at what frequencies, and what duration of these accelerations, is your son having these buildings designed for...or, never mind, not my expertise...
Chris