# Aerial Mapping of Coseismic Surface Rupture of 2021 M\({}_{\rm w}\) 7.3 Maduo Earthquake, China
## 3 Materials and Methods
### Drone Mapping  
Two field surveys were conducted in the first and third month after the Maduo earthquake, when the surface rupture was still fresh. A DJI Phantom 4 RTK (real time kinematic) drone was used to map the rupture. The RTK horizontal positioning accuracy of the drone was 1 cm + 1 ppm, and the vertical positioning accuracy was 1.5 cm + 1 ppm. The sensor was a 1 inch 20 megapixel CMOS, and the ground resolution of the drone can reach 2.74 cm at a 100 m flight altitude ([https://3 dinsler.com/dji-phantom-4-rtk-review/](https://3 dinsler.com/dji-phantom-4-rtk-review/); [[https://www.dji.com/cn/phantom-4-rtk](https://www.dji.com/cn/phantom-4-rtk)]([https://www.dji.com/cn/phantom-4-rtk](https://www.dji.com/cn/phantom-4-rtk)), accessed on 13 December 2022). With the GS RTK app, entering the coordinates of the four points of the rectangle, a route that followed the rupture was pre-programmed. At the main surface rupture site, the drone was flown in sections along the fault strike. The height of each flight was 25-100 m, the length was 200-500 m, and the width was 100-200 m. The front overlap and side overlap were set to 80%. The ground resolution of the drone was 1-3 cm. Once the drone captured the digital images, the data were imported into a workstation with a DJI processing system. By automatically recognizing the relative position and direction of each photo, aerial triangulation was calculated. 2D and 3D reconstructions were performed using the generated point cloud data. Finally, DEMs, orthophotos, and 3D models were generated (Figures 3-9 and S1A). Figure 2: A map of D-InSAR LOS coseismic deformation and sites investigated during the field survey with the locations of the corresponding figures of the paper. The dotted red lines indicate discontinuous rupturing of fault traces, and the solid red lines indicate continuous surface rupture. The color shading represents the amount of LOS coseismic deformation, and its values were obtained by analyzing D-InSAR data collected from the ascending orbit of the Sentinel-1 satellite. Figure 3: **(A)** Field operation of drone. (**B–F**) Coseismic surface rupture observed from the air. The red arrows point to the extension direction of the rupture. In (**D**), the collapsed Yematan Bridge is visible in the distance. In (**F**), landslides were caused on the slopes where the fault passed. Figure 4: Drone data processing results and fracture distribution statistics. (**A**) DEM of the surface rupture. (**B**) Orthophoto of the area shown in panel (**A**). (**C**) Fracture distribution and rose diagram, R shears, R\({}^{\prime}\) shears, and T fractures are major fractures. Figure 5: Orthophotos of the surface rupture and fracture distribution statistics. (**A**) R shears, R\({}^{\prime}\) shears, and T fractures are major fractures. (**B**) En-echelon shears and push-ups are major structures. Figure 6: Offsets and fracture distribution statistics. (**A**) DEM of the surface rupture. South side of the fault was uplifted, and the vertical offset is 0.69 m. (**B**) Orthophoto of the area shown in panel (**A**). En-echelon shears and push-ups are major structures. (**C**) 3D visualization of the surface rupture. The offset along the shear strike is 1.6 m, the included angle \(\theta\) between shear strike and fault strike is 37\({}^{\circ}\), then the offset along the fault strike equals to 1.6/\(\cos\) (37\({}^{\circ}\)), which is about 2 \(\pm\) 0.4 m.  
Figure 7: **(A)** DEM and (**B**) orthophoto of a fault scarp that ruptured during the earthquake. The height of the scarp is about 1 m in **(A)**. En-echelon shears and push-ups are major structures. A gully is visibly displaced. The offset along the shear strike is 1.4 m, the included angle \(\theta\) between shear strike and fault strike is 40\({}^{\circ}\), then the offset along the fault strike equals to 1.4/cos(40\({}^{\circ}\)), which is about 1.8 \(\pm\) 0.4 m.  
Figure 8: Push-up structures in the surface rupture.