## 3 Structural and Gas Distribution Characteristics of the Kaiping Syncline Turning End  
### Geological Structural Distribution Characteristics at the Turning End  
The Kaiping syncline has a NE-SW axial orientation, transitioning to an asymmetric syncline near the EW direction and becoming uplifted at the northeastern end. The geology on the northern side of the turning end in the Zhaogezhuang mine area is more complex, with faulting as the dominant structural form. Moving northward from the hinge, the faults shift from being primarily normal faults to predominantly reverse faults. On the southern side of the turning end, the Linxi mine has been affected by multiple phases of tectonic activity, with folding as the dominant structural feature. Major folds in the area include the Dujunzhuang Anticline and Heiyazi Syncline, accompanied by normal faults and dike formations (Figure 2a). Figure 1: Kaiping syncline structure diagram (**a**) and No.1 section diagram (**b**). The dip angle is a quantitative parameter that characterizes the structural features of a mining area and reflects the spatial orientation of strata. The magnitude of the dip angle can indicate the intensity of tectonic deformation. This study uses contour maps of the No. 7 coal seam floor to calculate dip angles in different areas of the study region in order to analyze and evaluate the structural distribution of the Kaiping syncline turning end. A grid of 2 km \(\times\) 2 km was superimposed on the contour map of the No. 7 coal seam floor (Figure 2b), and node data were extracted from the grid. Using an ideal dip angle calculation model, the dip values at the nodes were calculated (Figure 3) to reflect the extent of structural deformation and the degree of striatal inclination in the area. The dip angle at any given point (\(D\)) is calculated as follows:  
\[D=arctan\frac{D_{cl}}{V_{d}}\]  
In the formula, \(D\) is the dip angle value at a specific point on the coal seam floor, \(D_{cl}\) is the contour line difference of the coal seam floor, and \(V_{d}\) is the vertical distance between the contour lines of the coal seam floor. Using the contour data of the No. 7 coal seam floor at the turning end, this method was applied to quantitatively calculate the dip angles at various points on the floor. The contour map data for the No. 7 coal seam floor indicate that the contour distribution in the study area is characterized by \"north-south differentiation, with significant differences\". Structurally, deformation decreases from north to south, exhibiting a \"stepped\" change (Figure 3a). The calculation results show that the dip angles at the turning end range from 12.6\({}^{\circ}\) to 82.3\({}^{\circ}\), with an average of 29.3\({}^{\circ}\). A scatter plot of dip angles across different areas of the turning end indicates that the strata on the northwest limb are steep, locally upright, or overturned, with dip angles generally ranging from 60\({}^{\circ}\) to 85\({}^{\circ}\). The strata gradually  
Figure 2: Tectonic outline map of the study area (**a**); grid division diagram (**b**); contour map of stratigraphic dip angle at the turning end of the Kaiping syncline (**c**); scatter plot of stratigraphic dip angle in each structural zone (**d**). Notes: \(\frac{\chi\sim\gamma}{2}\), \(\chi\): minimum value; y: maximum value; z: average value. transition to gentler dips of 10\({}^{\circ}\) to 30\({}^{\circ}\) on the southeast limb, which are further complicated by a series of parallel secondary folds (Figure 2c). Based on geological data from the Linxi and Zhaogezhuang mines at the turning end, as well as the degree of structural development and dip angles, the two mining areas at the Kaiping syncline turning end are divided into six structural zones: west wing fault structure area, wellhead open syncline area, Kaiping syncline structural zone, monoclonal tectonic zone, Dujunzhuang Anticline structure area, and Heiyazi Syncline structure area (Figure 2c).