## 4 Result
### Paloseismic Studies
#### 4.2.2 TC2 Trench at Nidou  
The TC2 trench is located on an alluvial fan south of Nidou Village, Xiangcheng County. The Civu fault cuts across the alluvial fan, forming a linear fault trough. We obtained high-resolution geomorphic images and digital elevation data of the area around trench TC2 using UAV and SfM technology. The Civu fault has right-laterally displaced the gully on the southern side of the trench by 18 \(\pm\) 2 m (Figure 11). Descriptions of the strata revealed in trench TC2 are given from old to new as follows (Figure 12):  
Figure 11: (**a**) Tectonic landform near trench TC2 shown via UAV photogrammetry. The gully to the south of the site is right-laterally offset by approximately 18 \(\pm\) 2 m. (**b**) Photograph of the trench site.  
U1: Gray-yellow clay layer.  
U2: Gray-brown clay layer.  
U3: Yellow-brown powdery clay layer, containing a small amount of gravel.  
U4: Dark brown, dark gray silty sand layer, containing a small amount of small gravel particles, rich in organic material.  
U5: Gray-white, gray-brown silty sand layer, containing many small gravel particles, with grain sizes generally less than 3 cm.  
U6: Yellow-brown sandy soil layer, rich in organic material at the bottom, dark brown and dark gray in color.  
U7: Sandy yellow soil layer, rich in plant roots, with a small amount of gravel.  
On the basis of the faulted stratigraphy and deformation characteristics of the units in trench TC2, three paleoseismic events were identified. In event I, the fault primarily displaced unit U1, resulting in deformation of U1. Units U1 and U2 were in unconformable contact. The radiocarbon dates for samples NDC29 from U1 and NDC53 from U2 were 28,290 \(\pm\) 150 cal BP and 32,250 \(\pm\) 220 cal BP, respectively. However, the results for two other dating samples, NDC55 and NDC59, from the overlying unit U3 were 25,190 \(\pm\) 110 cal BP and 20,030 \(\pm\) 60 cal BP, respectively. Therefore, it was speculated that the test result of NDC53 was older than its actual age. Accordingly, the occurrence time of event I was constrained to between 28,290 \(\pm\) 150 and 25,190 \(\pm\) 110 cal BP. The evidence for event II was fault displacement of units U2 and U3, followed by the deposition of U4, which was in unconformable contact with U3. Unit U3 fractured, and subsequently, unit U4 locally formed some wedge deposition. According to the dating result of NDC24 in unit U4, event II likely occurred between 19,980 \(\pm\) 60 cal BP and 19,080 \(\pm\) 60 cal BP. The obvious evidence for event III was that the F1 and F2 faults displaced the U4, U5, and U6 units and that the activity of F1 caused significant folding and deformation in U4, U5, and U6. The age of the dating carbon sample NDC44 collected from the top of unit U6 was 2750 \(\pm\) 30 cal BP, suggesting that the occurrence of this event was close to this date. On the southern side of this trench site, the Ciwu fault has displaced a gully by approximately 18 \(\pm\) 2 m (Figure 11a). The exposed units U1-U5 in trench TC2 are clay or silty layers, representing the original sedimentation prior to the uplift of this terrace. Conversely, U6 and U7 are brown sandy soil layers with coarser sediment grain sizes, likely deposited after the uplift of the terrace and influenced by the fault activity. The fault formed the linear fault trough on the terrace, and subsequently, U6 and U7 were deposited in the fault trough. Therefore, according to the age of NDC02 from the top of U5 (8000 \(\pm\) 30 BP), we estimated that the right-lateral slip rate of the fault at this site was 2.3 \(\pm\) 0.3 mm/a.  
Figure 12: Photograph of the southern wall of the Bugge trench and explanatory profile. The radiocarbon dating sample ages of the TC2 trench are detailed in Table 2.