Geological structure in Zhengzhou area

1. Topography Zhengzhou City is located in the transition zone between the remnants of the East Qinling Mountains and the second and third landform steps in China. The overall terrain is high in the southwest and low in the northeast, showing a stepped decline. From the middle and low mountains eroded by structure in the west and southwest to the structural denudation hills, loess hills, inclined (hilly) plains and alluvial plains, a relatively complete geomorphological sequence has been formed. Among them, the middle and low mountains in the west and southwest are composed of Songshan Mountain and Jishan Mountain respectively, which are distributed in the middle zone of the west and the edge zone of the southwest in an east-west direction. The elevation of Songshan Mountain is generally 500- 1200m, with a relative elevation difference of 300——600m, forming the natural dividing line between Dengfeng, Xinmi, Gongyi and Xingyang. Its highest peak, Yuzhai Mountain, is1512.4m above sea level, which is the highest among all the peaks in this area. The topographic elevation of Jishan Mountain is generally 500-800 m, and the relative height difference is 200-400 m, which constitutes the southwest boundary of Zhengzhou City. Tectonic denudation hills are located in front of middle and low mountains, with an elevation of 200-500m and a relative elevation difference of100-200m. Influenced by formation lithology, the normal terrain of Yuanshan Tuling type is often formed in limestone and sandstone distribution areas, while the relatively low-lying negative terrain is formed in shale and mudstone distribution areas. Loess hills are located in the northwest and north-central part of the region, with an altitude of 200-300 m and a relative height difference of 30-150 m. The ground is criss-crossed with gullies and the terrain is broken. The inclined (hilly) plain is located in front of the hills, and the central area is distributed in a nearly north-south belt. Topographic elevation 100- 150m, inclined from west to east, vertical from the front of the mountain to the downstream, with a slope of 3- 10 degree, wavy from south to north and alternating hills. Alluvial plains are widely distributed in the eastern region, which are formed by alluvial of the Yellow River. The terrain is flat and the ground elevation is 80- 100 m, which inclines from northwest to southeast. 2. Stratigraphic lithologic areas are exposed in Archean, Proterozoic, Paleozoic, Mesozoic to Cenozoic except Silurian, Devonian and Jurassic. Archean is a set of schist, gneiss, granulite, phyllite, marble, magnetite quartzite, etc. Dengfeng Group has different degrees of deep metamorphism and migmatization. East-west distribution in the west of Songshan Mountain. Proterozoic is mainly composed of shallow metamorphic quartzite, quartz schist, dolomite, conglomerate, glutenite, timely sandstone mixed with shale, timely sandstone and shale of Luo Yu Formation. It is also distributed in the middle of Songshan and Lushan in the east-west direction. Paleozoic consists of CAMBRIAN limestone, shale and dolomite; Ordovician limestone, dolomite, siltstone, dolomite and shale; Carboniferous shale, clay rock, limestone, sandstone, coal seam, coal line and Permian sandstone, clay rock, coal seam and coal line are mainly distributed on both sides of Songshan Mountain and the northern slope of Lushan Mountain. Mesozoic consists of Triassic shale, sandstone, siltstone, claystone and sandy claystone, which are distributed between Songkou and Jishan. Cenozoic consists of Neogene semi-cemented claystone, sandstone, glutenite, marl and Quaternary loose silt, silty clay and gravel layers. The former is generally distributed in the valley bottom of the central hilly area and the loess hilly area in the northwest; The latter is widely distributed in alluvial plains in the east, loess hills in the northwest, and valleys and valleys between the central and western hills. In addition, there are intermediate intrusive rocks in Songyang and acidic intrusive rocks in Wuwangshan. The intrusive rocks in Songyang period are mainly diorite and granite, and some are gabbro, which are distributed in the west of Songshan Mountain and Shipai River in Dengfeng. The intrusive rocks in Wuwangshan are mainly biotite granite, which are distributed in the west of Songshan Mountain and Shuimowan-Shiping area in Dengfeng. 3. Geological Structure and Earthquake Zhengzhou City is located at the eastern end of the east-west complex structural belt of Qinling Mountains on the Sino-Korean paraplatform. Since Archaean, it has experienced three famous orogenic movements such as Songyang, Zhongyue and Shaolin, which have been superimposed and transformed in different periods and directions, forming an extremely complex structural form and framework in this area. According to its trace, it can be summarized as follows: (1) The north-south structure mainly occurs in the pre-Sinian strata and is contained by the east-west structure. It is the product of the orogenic movements such as Songyang and Zhongyue, and it is a strong north-south fold structure. Its folds are mostly closed compound anticlines with axial plane inclined west and reversed east, and the axial plane dip angle is generally 45 degrees. (2) East-west structure This structure is the main structure in this area, and it is a series of east-west faults and folds. Among them, the folding structure formed Songshan anticline, Jishan anticline and Angelababy-Ludian syncline between the two anticlines. Songshan and Lushan anticlines extend from east to west, parallel to each other, and are 1 10km long, which respectively constitute the middle and low mountains in the west and southwest of this area. The northern wings of the two anticlines are intact, and the strata are inclined to the north with an inclination of 20-30 degrees. The south wing of Songshan anticline is damaged by the east-west Wan Yue fault, and the dip angle is steep, generally above 40 degrees. Wan Yue fault is located in the south wing of Songshan anticline, nearly east-west strike, inclined to SSE, with an inclination of 45 degrees. The northern plate of the fault is Archean Dengfeng Group, Proterozoic Songshan Group and Wuwangshan Granite, which constitute the basement of this area. The southern plate of the fault is the caprock, that is, the Angelababy-Ludian syncline inclined eastward. (3) There are two groups of linear faults with NW 3 10-320 degrees and NE 15-30 degrees in the NW and NE tectonic systems, respectively. Among them, NW-trending faults are low in frequency but large in scale, represented by Wu Zhiling fault, Songshan fault and Ludian fault. NE faults frequently occur, but the scale is small, mainly including Wangtun fault, Shaolin Temple-Shuimowan fault and Yihe fault. According to the Ground Motion Parameter Zoning Map of China (GB18306-2001), the peak acceleration of ground motion in most areas in this area is 0.1-0.15g, which is equivalent to the basic earthquake intensity VII. The peak acceleration of ground motion in the southwest of Weidengfeng is 0.05g, which is equivalent to the basic earthquake intensity ⅵ. According to historical earthquake data, there have been no moderate earthquakes in this area, only a few weak earthquakes, and the seismic activity has the remarkable characteristics of few strong earthquakes and weak earthquake frequency.