Statistical features of aftershock distribution size for moderate and large earthquakes in Chinese mainland

Based on data of earthquake sequences with M S≥5.0 in Chinese mainland from 1970 to 2004, for different sequence types and different rupture modes of the main shock, the relationship between aftershock distribution size R and the magnitude of the main shock M 0 has been studied statistically. Considering the rupture mode of the main shock, we give the quantitative statistical relationships between R and M 0 under 95% confidence level for different sequence types. Qualitatively, lgR, the logarithm of the aftershock distribution size, is positively correlative to the M 0, but the data distribution is dispersed. Viewing from different sequence types, the correlation between R and M 0 is very weak for isolated earthquake type (IET) sequence, R distributes in the range from 5 to 60 km; For mainshock-aftershock type (MAT), lgR is positively correlative to M 0; For multiple main shock type (MMT), the correlation between lgR and M 0 is not very obvious when M 0≤6.2 and R distributes in the range from 5 to 70 km, while it shows a linear correlation when M 0≥6.3. The statistical results also show that the occupational ratios of different sequence types for strike-slip and oblique slip are almost the same. But for dip-slip (mostly are thrust mechanisms), the ratio of MAT is higher than that of IET and MMT. Comparing with previous results, it indicates that, when M 0 is large enough, R is mainly determined by M 0 and there is almost no relationship with the rupture mode of the main shock.