## 4 Discussion
### Asymmetry of the Damage Zone
#### 4.3.2 Driving Wall Effect in Strike-Slip Faults  
Previous studies have shown that the hanging walls of dip-slip faults generally suffer more damage than the footwalls, although the stress state and damage mode of the hanging walls and foot walls are not the same [75; 76]. In contrast, when it comes to strike-slip faults, the widths of the surface ruptures in both walls suggest that the damage should be distributed roughly symmetrically all along the fault core [23; 77]. However, based on our field investigations and data analysis, we found that the damage zones of the two walls of the XSHF are asymmetrically developed. The width of the damage zone of the SW wall is obviously wider than that of the NE wall (Figure 4, Table 1). One of the most important reasons behind the differential distribution of the damage zones across the XSHF may be due to the fact that the SW wall is a strike-slip driving wall. It is well known that fault slip begins with the loading of plate tectonic motion, and the direction of slip depends on the angle of oblique convergence of the plates and the direction of relative motion with respect to another plate [78]. The active Holocene left-lateral slip of the XSHF suggests that it was significantly controlled by the NE-trending extrusion and collision of the Indian Plate against the Eurasian Plate (Figure 1a). The current studies indicate that the slip rate of the XSHF gradually increased from NW to SE [43; 44], with a significant velocity difference between the two walls of the fault. This further suggests that the Sichuan-Yunnan block on the SW wall is less constrained than the Bayan Har block on the NE wall. The eastward movement of the Bayan Har block is absorbed by the high shrinkage rate and strong crustal compression caused by the LMSF, which shortens the crust [79; 80], whereas the clockwise rotation of the Sichuan-Yunnan block continues to extend into the north-south oriented fracture system [27]. This tectonic environment and the crustal kinematics have made the XSHF a large-scale left-lateral strike-slip fault to accommodate the different movement rates between the Chuan-Dian block and the Bayan Har block. The response pattern of the rock mass to the loading provides insights into the movement of faults. The mechanical test results indicate that during quasi-hydrostatic loading of granite and sandstone, the volume expansion of granite and sandstone becomes more obvious as the strain rate increases [81], showing a positive correlation between the strain rate and rock damage [82]. The XSHF is located in an area comprising granite and sandstone lithologies, and the numerical inversion results reveal that the SW wall experiences a high strain rate environment, whereas the strain rate decreases rapidly from west to east on the NE wall [43; 83]. This suggests that the stronger activity of the SW wall has caused a wider rock damage zone in the study area. In the context of the India-Asia collision, the Sichuan-Yunnan block, i.e., the SW wall, acts as a driving wall, resulting in the width of the damage zones of the SW wall being generally wider than those of the NE wall.