I mean, we can't really measure it in any way besides either calculating the feat or just taking the highest number it gave, even if it states it cannot be "measured", as we really don't have any other way to measure it.
If you have some numbers like how diameter, and depth of the circle made, you could calculate it or request a calculation, or if there were more proof that it shook the entire seawater of the location (if it was an ocean for example, and there was proof it shook all of it), you calculate that as well.