Born Thursday 26 April 1900, died Saturday 20 April 1985
We would have been happy if we could have assigned just three categories, large, medium, and small; the point is, we wanted to avoid personal judgments. It actually turned out to be quite a finely tuned scale.
I repeatedly have to correct this belief. In a sense, magnitude involves steps of 10 because every increase of one magnitude represents a tenfold amplification of the ground motion. But there is no 'scale of 10' in the sense of an upper limit.
From here, it becomes an engineering problem; the engineer considers the ground motion that will occur and evaluates the requirements of the proposed structure in the light of the local foundation conditions.
For example, some stars put out large amounts of energy in the infrared part of the spectrum, so that this can produce a different relative magnitude rating than using light energy from the middle of the spectrum.