Abstract: Tianjin Fault includes south Tianjin Fault and north Tianjin Fault.Based on the results of artificial seismic exploration,four borehole profiles were laid out respectively at west of Jinghai county town,Chaomidian village of Xiqing district,Xiaonanhe village of Xiqing district,and Zhutoudian village of Ninghe county to implement the exploration of these faults.Through identification of microfossils,the locations of marine strata in boreholes were obtained in this work,and through stratigraphic dating,the ages of the first,second and third marine strata were determined.Through strata contrast with the marine strata as key marker horizons and integrating with the test results of paleo geomagnetism of BZ2 and TN3 bores,the activity of north Tianjin North and south Tianjin Fault was analyzed.The result indicates that there have been no signs of movement of the south Tianjin Fault since late Pleistocene,and it might have weak activity before middle Pleistocene.No sign of activity of the north Tianjin Fault has been found since late Pleistocene either,and it might be active in the early stage of early Pleistocene.These show that the activity of the south Tianjin Fault is stronger than that of the north Tianjin Fault.At the same time,we find that the second,third and fourth marine strata are lacking to some extent in different areas.So,before they are used in strata contrast,the age of marine strata must be determined,otherwise the results of strata contrast may lead to mistake.For the second marine stratum,where there has been dispute about its age,we consider the age is about 70ka or so.

Key words: Tianjin Fault, marine strata, strata contrast, fault activity

摘要： 天津断裂分为天津南断裂和天津北断裂。根据人工地震探测结果,分别在天津静海县城西、西青区炒米店村、小南河村以及宁河县朱头淀村布设了4条钻孔剖面,对这2条断裂开展了钻孔勘探工作。经微体古生物鉴定,获得了各钻孔的海相层位置;经地层年代测试,确定了第1、第2和第3海相层的年代;通过以海相层为标志层的地层对比,并结合小南河村BZ1、TN3孔古地磁的测试结果,对这2条断裂的活动性进行了分析研究。结果表明,天津南断裂晚更新世以来未发现有过活动的迹象,其最新活动年代可能在中更新世。而天津北断裂也未发现晚更新世以来存在活动的迹象,该断裂在早更新世早期可能有过活动。由此可见,天津南断裂活动性可能要强于天津北断裂。同时发现,第2、第3、第4海相层在不同的地区存在不同程度的缺失现象。因此,在将其用于地层对比时,必须同时确定各海相层的地质年代,否则对比结果可能会出错。对于发生年代存在争议的第2海相层,认为其形成时间应在7万a左右。

关键词: 天津断裂, 海相层, 地层对比, 断层活动性