What is the geographical environment of Qidong?

Qidong is bordered by the north branch of the Yangtze River estuary in the south, the center of the Yangtze River in the east, Yonglongsha bordering Chongming District in Shanghai in the west, the national expressway network G40 crosses Qidong, and the Chongqi Bridge is connected with Chongming Island in Shanghai. The east and north are adjacent to the Yellow Sea, and the west is adjacent to Haimen City.

Qidong city belongs to the humid climate zone in the north subtropical zone, with obvious maritime monsoon climate characteristics, four distinct seasons, abundant sunshine, mild temperature, abundant rainfall, long frost-free period, changeable weather in spring and refreshing weather in autumn, with average air pressure 10 16.5 hectopascals, annual average temperature 15℃ and annual average precipitation/kloc-. The annual maximum wind direction is southeast wind with an annual average wind speed of 3.5m/s; The annual average sunshine hours are 2073 hours; The average annual frost-free period is 222 days. Among them, Yuantuojiao in Yinyang Town is the earliest place to see the sunrise in Jiangsu.

The territory is flat and criss-crossed with rivers and ditches, belonging to low-lying coastal areas. The topography of the micro-domain is slightly undulating and slightly inclined from northwest to southeast. Daoan River is the natural dividing line between north and south landforms. The elevation of Henan (Wusong elevation) is 3.6 ~ 4.6m, that of Hebei is 5. 1 ~ 6. 1 m, and the north-south dip angle is about1/30,000m. The east-west dip angle is about 1/43500m. The annual groundwater level is 1.2 ~ 1.6 meters.

Within the range of 17m below the natural ground, there are mainly: the general thickness of the filled soil layer (or cultivated soil layer) is 0.6 ~ 1.0m, and the soil is soft. The second layer is silty clay, and local silty clay is sandwiched with silty clay thin layer. The thickness of this layer varies from 2 meters to 4 meters, which is a good bearing layer for general building foundations. The lower layer is interbedded with silty clay, and there is a thin layer of silty sand locally, which is relatively uniform. From west to east, silty clay is mainly interbedded, and the thickness gradually increases by about 7.5 ~10.0m, with high bearing capacity and soil layer. Generally speaking, the bearing capacity of Qidong foundation is 10 ~ 13t/m2, which belongs to the alluvial plain near the river and the sea.

Qidong crystalline basement is deeply buried and its lithology is weak and flexible, so it is difficult to meet the rock conditions of strong earthquake activity. Since Cenozoic, depression has dominated, showing large-scale subsidence movement, forming basins and plains, with large stratum plasticity and weak fault deformation. Since Cenozoic, most of the active faults are synsedimentary fault, and the energy is easy to release but not easy to accumulate, and the uplift operation has obvious oscillation, so it is not easy to breed strong earthquakes in this area.