The Tianjin fault includes South Tianjin fault and North Tianjin fault.Based on the results of artiffcial seismic exploration,fonr borehole profiles were laid out respectively 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 beds in boreholes were obtained in this work,and through stratigraphic dating,the ages of the first,second and third marine beds were determined.Through strata correlation with the marine beds as key marker beds and integrating with the test results of paleo geomagnetism of boreholes BZ2 and TN3,the activity in the North and South Tianjin faults was analyzed and studied.The results indicate that there is no evidence of movement of the South Tianjin fault since the Late Pleistocene,but may have had weak activity before the Middle Pleistocene.No evidence of activity in the North Tianjin fanit was found since the Late Pleistocene either,but might have been active in the early stage of the 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 beds are lacking to some extent in difierent areas.So.before they are used in strata correlation,the age of marine beds must be determined,otherwise the results of strata correlation may lead to errors.For the second marine bed,where there has been dispute about its age,we consider the age to be about 70ka.