[Repeal The 17th]

I think it is:
a 9 is 10 times an 8
an 8 is ten times a 7
a 7 is ten times a 6
a 6 is ten times a 5
and so forth and so on.

[ImaGraftedBranch]

I believe a 7.1 is 10x stronger than a 7.0, etc.

[Errant]

Thanks, I had did have it wrong.. It's two numbers up that has 1,000 times the energy (so in this case, a mag 10 would be 1,000 times more powerful than an 8 - I think :-)):

"31.6227 to the power of 0 equals 1, 31.6227 to the power of 1 equals 31.6227 and 31.6227 to the power of 2 equals 1000. Therefore, an 8.0 on the Richter scale releases 31.6227 times more energy than a 7.0 and a 9.0 on the Richter scale releases 1000 times more energy than a 7.0. Thus, E \approx 6.3\times 10^4\times 10^{3M/2}\,"

https://en.wikipedia.org/wiki/Richter_magnitude_scale