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

Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; in terms of energy, each whole number increase corresponds to an increase of about 31.6 times the amount of energy released.

簡單地說，10 倍是算地震的振幅，32 倍是算地震釋放的能量。