中国大陆中强以上地震余震分布尺度的统计特征

STATISTICAL FEATURES OF AFTERSHOCK DISTRIBUTION SIZE FOR MODERATE AND LARGE EARTHQUAKES IN CHINESE MAINLAND

依据1970年以来记录相对完备的Ms≥5.0地震序列资料,统计研究了中国大陆余震分布尺度与序列最大地震震级M0及最大地震破裂形式之间的关系.在95%置信概率下,考虑主震破裂形式,分序列类型给出了余震分布尺度与M0之间的统计关系.定性而言,余震分布尺度的对数lgR与M0正相关,但数据分布较为离散.分类型来看,孤立型序列余震分布尺度与M0之间统计相关程度低,余震分布尺度介于5～60 km之间;主余型序列lgR与M0正相关;多震型序列当M0≤6.2时lgR与M0之间相关性不显著,余震分布尺度介于5～70km之间,当M0≥6.3时lgR与M0线性相关.统计结果还表明,走滑-近走滑及斜滑型主震所导致序列类型比例之间没有显著差异,而倾滑-近倾滑型主震（主要为逆断型破裂）所导致的主余型序列所占比例较高,孤立型及多震型序列所占比例则相对较低.对比研究显示,当M0较高时,余震分布尺度主要取决于主震大小而与主震破裂形式关系不明显.

Based on data of earthquake sequences with Ms≥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 M0 has been studied statistically. Considering the rupture mode of the main shock, we give the quantitative statistical relationships between R and M0 under 95% confidence levels for different sequence types. Qualitatively, lgR, the logarithm of the aftershock distribution size, is positively correlative to the M0, but the data distribution is dispersed. Viewing from different sequence types, the correlation between R and M0 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 M0; For multiple main shock type MMT, the correlation between lgR and M0 is not very obvious when M0≤6.2 and R distributes in the range from 5 to 70 km, while it shows a linear correlation when M0≥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 M0 is large enough, R is mainly determined by M0 and there is almost no relationship with the rupture mode of the main shock.