# Quaternary Segmentation Characteristics of the Hunhe Fault, Northeast China
## 5 Discussion
### Seismic Activity of Fushun Segment  
The Fushun graben-like faulted basin, which developed along the Hunhe fault zone, primarily took shape during the Paleogene, with significant tectonic activity in this period. However, during the Neogene, the fault's activity weakened considerably. Since the Quaternary, the basin has undergone slight east-to-west tilting and subsidence, reflecting ongoing but limited tectonic movements. The structural foundation of this region is influenced by the Jiao-Liao uplift to the west and the Tieling-Jingyu arch to the east. The fault also marks the boundary between the northern Panhe Depression and the southern Fushun uplift, playing a crucial role in controlling the distribution of both the basement and overlying cover layers. While the fault zone crosses different Neotectonic divisions on either side, the differences in tectonic characteristics between these divisions are minimal. This suggests that the overall regional tectonic processes remain relatively consistent across the fault, despite the division into separate structural blocks. In terms of macro-geomorphology, this fault segment is situated in the transitional zone between the Lower Liaohe Plain and the Liaodong Mountains. The fault zone's southern and northern branches extend along the south and north sides of the Hunhe River valley, respectively, shaping the basin's geomorphic features and Quaternary deposits. The near-surface geomorphic units of the basin include the first-level Hunhe River terrace, floodplain, and piedmont inclined plain, while outside the basin, there are second to third-level basement terraces and eroded, denuded hills. The thickness of the Quaternary deposits increases gradually from 5 to 10 m in the eastern end to about 20 m in the western end, with an incomplete sequence, notably lacking MIS 20-103-MIS6-19 strata. The fault is concealed beneath the Quaternary deposits in the basin, with no observable fault scarps or micro-relief features near the surface. However, in the mountain-front zones on either side of the basin, curved to nearly straight micro-relief scarps and slopes are visible along the fault, along with valleys and other negative landforms extending along the fault. In some areas, the fault zone is exposed along these slopes and scarps. The results from the artificial seismic method [16] indicate that the large-scale Hunhe fault segment in Fushun significantly displaces the bedrock strata but does not cut through the overlying MIS 2-5 strata. This segment falls within a gravity field characterized by negative anomalies, with relatively complex magnetic variations (Figure 11). The area north of the fault zone is a negative field region, while the south is predominantly a positive field region. The crustal thickness is greater than in the Shenyang segment, and the east-west gradient variation transitions to a north-south direction, indicating a transitional zone. Seismic activity in this fault segment is much weaker than in the Shenyang segment, with only one significant earthquake recorded near the fault--an M5.0 earthquake at Dongzhou Fort in 1496 [27]. Aside from this, there are no records of destructive earthquakes, and recent seismic activity is also notably reduced, mainly consisting of mining-induced seismic events. These minor tremors are generally aligned along an NEE trend, with locations close to the Hunhe fault, suggesting a correlation between mining activity and the fault. Overall, the Hunhe fault segment in Fushun has experienced multiple phases of tectonic activity of different natures. Early thrusting activity pushed Archean formations over Cretaceous ones, and Cretaceous formations over Paleogene layers, resulting in the inversion of coal-bearing strata. Activity was relatively strong before the Paleogene but decreased significantly afterward, with further reduction during the Quaternary. As a result, structural breccia and fault surfaces from pre-Quaternary activity have often been preserved.