Several Key Basic Geological Problems on the Development of the Guanzhong Urban Agglomeration

The Guanzhong Basin is a fault basin, has complex geological structure, developed active faults and frequent seismicity, which cause a series of important basic geological problems in urban construction. On the basis of collecting and analyzing more than 1000 kinds of drilling data in the Guanzhong Basin, we have studied the main drilling wells and profiles in the 1:50,000 comprehensive geological survey of the Guanzhong Basin Urban Agglomeration, and then discuss some basic geological problems in this paper, such as the basin formation and evolution, the avoiding of active faults, the three-dimensional geological structure reconstruction of the Guanzhong Basin, the evolution of drainage system, the development of cities, ancient flood events in historical period and the construction of sponge city. The results show that:(1) The Guanzhong depression was formed in the middle and late Cretaceous, and the lakes began to form in Eocene. After many faults and uplifts, two sedimentary centers were formed. By Pliocene, these lakes expanded to the maximum extent. Since Quaternary, the basin has been in a continuous and slow process to decline and accept sediments. Affected by the continuous tectonic uplift of Qinling Mountains, these sedimentary centers migrated from south to north, which will affect the layout of urban agglomerations greatly. Thus, the construction of urban agglomeration in the Guanzhong Basin must be far away from the junction of faults, the end point and the pivot of fault movement. (2) It is suggested that the Lvsanmen Formation should be classified into Pliocene instead of Quaternary. The formation age of the Sanmen Formation has the characteristics of diachronis, which needs to be attention and correction when planning Quaternary and underground space in the Guanzhong Basin. (3) Urban planning and construction should follow the natural law of river and lake evolution and regional geological landform characteristics. The once-in-a-millennium precipitation is 900 mm, which can be regarded as the design basis for urban flood control and sponge city construction.