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

Based on data of earthquake sequences with MS≥5.0 in Chinese mainland from 1970 to 2004,for different se-quence types and different rupture modes of the main shock,the relationship between aftershock distribution size Rand the magnitude of the main shock M0 has been studied statistically.Considering the rupture mode of the mainshock,we give the quantitative statistical relationships between R and M0 under 95%confidence level for differentsequence types.Qualitatively,lgR,the logarithm of the aftershock distribution size,is positively correlative to theM0,but the data distribution is dispersed.Viewing from different sequence types,the correlation between R and M0is very weak for isolated earthquake type(IET)sequence,R distributes in the range from 5 to 60 km;For main-shock-aftershock type(MAT),lgR is positively correlative to M0;For multiple main shock type(MMT),the core-lation between lgR and M0 is not very obvious when M0≤6.2 and R distributes in the range from 5 to 70 km,whileit shows a linear correlation when M0≥6.3.The statistical results also show that the occupational ratios of differentsequence 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 M0is large enough,R is mainly determined by M0 and there is almost no relationship with the rupture mode of themain shock.

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. Foundation item: Joint Seismological Science Foundation of China (105076) and continued subject “Statistical Features of Aftershock Sequences and Forecast of the Large Aftershocks” (2004BA601B01-04-02) and Ministry of Science and Technology of China in the 10th Five-year Plan.