By analyzing the aftershock data of the 1976 Tangshan earthquake with higher category of epicentral location accuracy, a clear distribution pattern of three bands of aftershocks trending NE, NWW, and NW respectively has been identified. The analysis explains that the aftershock bands have revealed the three rupture planes of strong events with magnitude 7. 8, 7. 1 and 6. 9 respectively during the sequence. It indicates that the above pattern is related to the source and NE, NWW, and NW trending fault zones based on the research of pre-seismicity pattern. In summary, the source is located in the crossarea of the three fault zones, and the rupture planes of the three strong events located in the source should be regarded as the locked segments on the three fault zones. In conclusion, our analysis has explained the complexity of the source and epicentral distribution of the aftershock sequence.%本文采用唐山地震序列定位精度较高的资料,对不同时段余震震中分布进行再分析,取得了余震密集带和序列3次强震(唐山7.8级、滦县7.1级、宁河6.9级)破裂面分布的清晰图像,其中判定7.1级地震为NWW向破裂面.其复杂图像与震前地震活动异常所揭示的震源及与震源孕育有关的三组区域性断裂带存在密切联系.简单说来,震源位于NE向、NWW向、NW向三组断裂带交汇的区域,位于震源的余震密集带显示了这3次强震的破裂面,它们分别可看作是三组区域断裂的闭锁段.据此解释了形成唐山地震震源和序列震中分布复杂性的原因.
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