Since Archaean, Beijing has experienced many tectonic movements, which have transformed the original structures and strata to varying degrees, among which Yanshan movement played a key role in the formation of the structural pattern in Beijing. It not only folds the strata, but also forms a series of NE faults such as Zijinguan and Babaoshan, forming Jingxi Uplift, Beijing Uplift, Daxing Uplift and Dachang Uplift, and the edges of the uplift and depression are controlled by NE faults. Himalayan movement changed the NW-SE compression direction into NW-SE extension direction, forming NW-trending fault structure, which controlled the formation and evolution of Beijing Plain landform. Due to the division and activity of the two main cross faults in NE and NW directions, the stratigraphic differences fluctuate, forming a checkerboard pattern. Since Cenozoic, NW-trending fault activity has intensified, mountains have been rising, plains have been falling strongly, and a series of Quaternary sedimentary centers have been formed by receiving extremely thick sediments. Since then, the structural framework of the plain with two ridges and one depression has disintegrated.

Figure 9- 12 Temperature changes at different depths in Beijing Yongfeng area during the year.

Fig. 9- 13 Curve of Formation Temperature with Depth in Beijing Olympic Forest Park

It can be seen from Figure 9- 1 1 that the distribution and change of geothermal field are obviously related to geological structure. On the plane, the contour lines of geothermal field in Wali, Niulanshan, Shahe and other high areas are distributed in a closed way, all of which are in the northeast direction and distributed near the fault. The ground temperature in Beijing sag is obviously higher than that in its neighboring areas. The ground temperature in this area is generally 22℃ ~ 30℃ at 70m underground, 27.4℃ at JR-63 geothermal well near Jianguomen, and 29.2℃ at Quaternary bottom boundary 145m. Generally, the geothermal gradient in this area is 3℃ ~ 5℃/100m, and it is 14.32℃ 50 meters away from the JR- 178 geothermal well on the Daxing uplift in the footwall of Nanyuan-Tongzhou fault, and 18.95℃ at the bottom of Quaternary system. On the profile, the ground temperature near the fault zone reaches the highest value at the same height (Figure 9- 14). The ground temperatures of I-75 above Babaoshan fault zone and I-88 above Huangzhuang-Gao Liying fault zone are higher, and the ground temperatures at 70m are 15.9℃ and 2 1.22℃ respectively, which decrease rapidly away from the fault zone. The structure in Beijing area is relatively developed, and it has experienced many tectonic movements such as Indosinian movement, Yanshan movement and Himalayan movement, forming many NW-trending and NE-trending fault zones, and even some faults are still active today.

Fig. 9- 14 Profile of Relationship between Ground Temperature and Faults in Beijing Area

The fracture strongly breaks or lifts the bedrock, and the formation of cracks provides a good channel for the deep heat source, thus making the ground temperature near the fracture higher; The buried depth of Paleozoic and Mesoproterozoic limestone in Niulanshan-Shunyi area is about 250 meters, and the ground temperature at 70 meters is higher than 65438 06℃, which is obviously controlled by bedrock cracks.