Abstract: Based on the G-R relationship and nonlinear dynamics, we have proposed some statistical variances, i.e., magnitude variation coefficients δ_m, b value, magnitude entropy H(m), Markov chain theoretical value h and information fractal dimension D₁ etc., to describe the different kinds and properties of earthquake sequences. We have also discussed the physical meaning for cutoff magnitude, b value, average magnitude , h and D₁. It is helpful to distinguish and early judge the type of earthquake sequences (foreshock, precursory swarm and mainshock-aftershock type, strong shock swarm type, isolated strong shock type) by δ_m, b value, H(m), different ΔH(m) between H(m), and theoretical exponential magnitude entropy H(∞)。

Key words: Magnitude variation, Earthquake sequence, Statistical feature, Judgment for earthquake sequence′s type