Reply #57: From my old Geophysics textbook, circa 1985

[daleo]

(Introduction to Geophysics, Garland)
Magnitude, number per year, description
8, 1.1, Great Earthquakes
7-7.9, 18, Major Earthquakes
6-6.9, 120, Destructive Earthquakes
5-5.9, 800, Damaging Earthquakes
4-4.9, 6200, Minor Earthquakes
3-3.9, 49000, Smallest generally felt
2-2.9, 300000, Sometimes felt

So, a magnitude 9.2 is very rare and very powerful - literally off the scale, in this case.

My old geology textbook (Introduction to Geology, Stokes, Judson, Picard) doesn't show any recorded earthquakes greater than 8.6. The San Fransisco earthquake of 1906 was estimated to be magnitude 8.25. It also gives the energy release of a magnitude 9.0 earthquake as 179,000,000 tons of TNT, or 179 Megatons. A magnitude 9.2 would probably be significantly more (the scale is logarithmic), so lets say about 400 Megatons.

I am actually surprised by these latter figures, which I would have expected to be much higher. It puts the Russian 60 MT nuclear test of the early 1960s into some perspective.