An Analysis of Fault Activities in Eastern Beidagang Tectonic Belt, Tianjin
天津北大港构造带东翼断裂活动浅析

Structural factors play a controlling role in the distribution of oil and gas,and oil and gas enrichment and distribution in a basin or in a sag depend on characteristics of fault activities.The authors carefully studied all the fractures in eastern Beidagang tectonic belt,calculated and analyzed fracture distance variations of 20 large faults in vertical and horizontal directions in combination with over 20 seismic sections and 8 structural development profiles in the study area.On such a basis,the authors hold that the main fault activities in eastern Beidagang tectonic belt occurred in Paleocene tectonic period and Neocene tectonic period.In Neocene tectonic period,however,fault activities were extremely weak,and most faults were not active.From evolutionary process and spatial distribution,it is considered that the destructive effect of late tectonic activities on earlier faults was weak,and fault activities were somewhat similar to things of Baishuitou tectonic belt in Gangdong-Tangjiahe tectonic belt,forming a typical flower-shaped structure.Nevertheless,fault activities in Baidong tectonic belt were strong in Neocene tectonic period,and some new faults cut Paleocene strata with some reaching the near-surface place,forming "face toward sloping type" fault combination.The influence of fault activities on hydrocarbon migration and accumulation is also preliminarily discussed in this paper.