关键词: 天津断裂, 海相层, 地层对比, 断层活动性

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