In this case, I used threshold and lower limit interchangeably - as there was only the one limit. The verb is still the (minor) problem.

"Sub" is interesting. I wonder if there's a "sub" word that corresponds to "exceeded." Subduct seems like it should work, but geologists already use it. Also it kind makes it sound like the boundary moved instead of the measurement across the boundary. I could try and see if my editor or colleagues would easily infer the meaning.

"The lower limit was subducted."