沧州地区NWW向隐伏断裂存在依据及其地震地质意义

The Existing Evidences of NWW Buried Fault in Cangzhou Area and Its Seismogeological Significance

摘要:

经过对河北沧州地区中强地震和小震空间分布分析发现,存在NNE向条带分布,与大规模的河北平原地震带的走向一致;同时也呈现了明显的NWW向条带,与NNE向组成共轭构造图象。对比2次中强地震,其震源机制解基本相同,有近于直立的NWW向节面做左旋走向滑动;3次地震烈度的极震区长轴方向也是NWW;1967年河间6.3级地震之后5天的余震分布也是NWW方向。这和历史上5级地震分布方向一致。虽然没有浅表断层的对应,多种资料的相互验证表明沧州地区深部存在一条NWW向的隐伏断层,对于判别区内地震危险性具有重要意义。

Abstract:

Based on the analysis of earthquakes distribution in Cangzhou area,it is found that there exists a NNE belt of small earthquakes,which is consistent with strike of the Hebei plain seismic belt.In addition,middle and strong earthquakes show obvious NWW-striking distribution,constructing conjugate structure image with the NNE striking belt.Comparing the focal mechanisms of 2 moderate-strong earthquakes,they are similar and have a nearly vertical NNW fault plane doing left-lateral strike-slip movement.The long axis directions of intensity in the meizoseismal area for 3 earthquakes are NWW.The aftershocks distributed in NWW direction within 5 days after the 1967 Hejian M6.3 earthquake.This character coincides with the distribution direction of historical earthquakes with M≥5.Although there is no relevant shallow fault,mutual verification of many kinds of information reflects that there exists a deep buried fault with NWW striking in Cangzhou area.Therefore it can be regarded as the potential seismic source of seismic risk analysis.