## 4 Results
### Hanqingba Village (Site 1)
#### 4.1.2 Evidence for Fault Activity and Parameters  
To obtain fault profile information at Site 1, the HQB trench was excavated at the western end of the scarp, where the surface linear feature is most distinct. The HQB trench crosses the fault scarp and extends along a NW 323\({}^{\circ}\) orientation, with its GPS location at 41\({}^{\circ}\)06\({}^{\prime}\)46.01\({}^{\prime\prime}\) N, 112\({}^{\circ}\)53\({}^{\prime}\)45.01\({}^{\prime\prime}\) E.  
Seven units were defined within the west wall of the HQB trench (Figure 5), and the specific descriptions of the stratigraphic units are as follows:  
1. U1: Bedrock layer, gray-black, consisting of volcanic tuff forming the platform base.
2. U2: Colluvial layer, reddish-brown, composed of medium to coarse sand mixed with fine gravel, representing typical wedge-shaped deposits in front of the scarp. The composition is mixed, primarily derived from the highly weathered and loose volcanic tuff of U1.
3. U3: Alluvial layer, earthy yellow, with some directional features, small gravel size, and moderate consolidation.
4. U4: Clay layer, yellow to reddish-brown, composed of fine silt to silty sand. It is inferred to be a stagnant water deposit in front of the scarp or a locally developed sedimentary lens, showing tight consolidation.
5. U5: Alluvial layer, yellowish-brown, with poor sorting and rounding, small gravel size, and loose consolidation.
6. U6: Alluvial layer, gray-white to earthy yellow, containing larger gravel clasts. The lower sediments show calcification and whitening, suggesting deposition from multiple alluvial events during the same period. The composition is relatively consistent, with poor sorting and rounding, and moderately tight consolidation.  
Figure 4: Orthomosaic image (**A**) and DEM (**B**) at Site 1 based on UAV data.  
U7: Paleosol layer, black-yellow, containing medium to coarse gravel. It is soil-like and loosely consolidated.  
These units can be classified into two main sections delineated by a clear fault (Figure 5). On the north side of the fault plane, the strata consist of typical gray-black volcanic tuff, showing some degree of weathering but with distinct characteristics of the original bedrock (U1). On the south side of the fault plane, multiple phases of alluvial events were identified, forming typical alluvial fan deposits (U3 and U5). A colluvial wedge deposit was developed on the southern side of the fault plane, closely adjacent to the fault surface. It consists mainly of highly weathered volcanic tuff material that is heavily argillized, contrasting sharply with the tuff on the northern side (U2).  
The clear fault in the trench profile indicates that the most recent surface faulting event occurred before the deposition of U2. The U3, U4, and U5 strata show thickened deposition in front of the scrap, displaying typical post-seismic scarp-front deposition characteristics. On the northern side, the U3 and U5 alluvial strata are absent above the U1 bedrock, while the U6 layer shows no absence or thickness variation. This suggests that fault activity persisted until the deposition of U6. The U3 and U5 layers in the trench are typical alluvial gravel deposits, predominantly composed of gravel, making it impossible to collect OSL samples. In contrast, U4 is a 20-30 cm thick yellow to reddish-brown clay layer, indicative of stagnant water deposition. To further refine the timing of fault activity, one OSL sample (WOSL-9) was collected from the base of U4 at a consistent location (Figure 5). OSL dating results indicate that the sediment age of U4 is 378 \(\pm\) 31 ka B.P., in the Middle Pleistocene.  
By interpreting the eastern wall profile of the Hanqingh trench (Figure 6) and comparing it with the western wall, the stratigraphy revealed by both walls is generally consistent, clearly confirming the presence of the JRNF.  
Figure 5: Photomosaic of the west wall of the HQB trench (**A**) and the corresponding trench map with results for OSL ages (**B**).  
Figure 6: Photomosaic of east wall of HQB trench.