Characteristics of northern section of Beijing Babaoshan fault based on the stratigraphic data of geothermal drillings

Basing on the stratigraphic data of geothermal drillings, a geological profile is plotted across the north segment of Babaoshan fault zone, and deep structure is discussed. According to the lateral stratigraphic alignment, it is found that there are many reverse-faults in different scale and inclination in the section, and these faults are dislocated mutually, which reflects that the thrusting effect of the Babaoshan fault is very strong and is of multiphase. Meanwhile, there are two larger faults in the section. One is the main fault of the Babaoshan fault zone, and the other is the minor fault resulted from the blocking of Wumishan formation put upwards by the main reverse fault. Because the main fault is covered by hanging wall of the minor fault for the thrusting of the minor fault is so strong, therefore in the Babaoshan area, there only one fault line appears on the surface, and the fault we normally refer to as the Babaoshan fault. We can see it is not the main fault line of the fault zone, which should be carefully examined in the research and monitoring of the fault zone. According to the rough estimation basing on the stratigraphic data of geothermal boreholes, it is deduced that the dip angle of the main fault is about 40 degrees, and the maximum cutting depth is about 5 000 m. In additional, the relation between stratigraphic cutting and deposition reveals that the Babaoshan fault was formed appro-ximately in the Late Mesozoic era.