just how big is a 9.0 earthquake

really big by many of our standards

A few calculations show the energy release of a 9.0 earthquake is about 1.33 * 10²⁰ joules ... 133 exajoules¹ for those of you who like fancy terms.. My Physics Vade Mecum notes the total energy consumed in the United States in 1985 was 79.8 exajoules with 30.85 exajoules being provided by oil.

Rounding a small amount, this is the amount of energy produced by converting 1500 kg of matter into energy using Einstein's famous relation E=mc² - about the mass of a medium sized car. Converting it into explosive equivalents we get 32,000 million tons of TNT. 1 megaton is a largish H bomb, so think about 32,000 of them. I doubt the total potential weapons yield on the planet is that large.

This is a horrible event, but we are lucky that events like these are as diffuse as they are. An H bomb dissipated over a similar area is a minor event.

I heard one comment on the radio that the Earth's rotation was speeded up by 2 or 3 microseconds. This is quite a bit, but note the Earth-Moon tidal interaction slows the Earth by 15 microseconds a year (calculating this is a standard Physics prelim problem), so the rotational slowing is not significant.

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¹ For those of you who prefer BTUs I note that a "quad", 10¹⁵ BTUs, is about 1 exajoule. This reminds me of a great Feynman quote:

For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy.