Abstract: The Dasi fault passes through the urban area of Tianjin, however, there is no systematic exploration or research on it. Therefore, the evidence for its spatial distribution and Quaternary activity is insufficient. According to the data of drilling, gravity, magnetotellurics etc., the cutting depth of the Dasi fault is greater than 10 km. Before the Neogene, great normal fault activity happened along the Dasi fault, and resulted in the remarkable denudation of the footwall. In consequence, the Dasi fault has become the west boundary of the Neopaleozoic and Mesozoic strata that distributed to the east of it. The activity of the Dasi fault was relatively strong in the Meso-Cenozoic and became weaker since the Quaternary. Combined with the latest results of shallow artificial seismic exploration, this paper determined the structural characteristics, the spatial distribution and active age, etc. of the Dasi fault. The Dasi fault has a total length of about 36 km. It generally strikes NNE and dips to the E. It starts from the north of Hulianzhuang, passes through the east of Tuanbo, the west of Dasi, the southeast of the urban area, and ended at the east area of the Wanxinzhuang, Dongli District. The latest active age of the Dasi fault is the late Middle Pleistocene. A small branch fault developed south to the Chentangzhuang is about 5 km long with NEE trending and NW dipping. Its latest active age is Middle Pleistocene.

Key words: Dasi fault, Shallow seismic exploration, Structural characteristics