# Quaternary Activity and Paleoearthquakes of the Fushan Fault, Shanxi, China
## 3 Results  
### Stratographic and Paloseismic Record Within the Fushan Fault Trench  
The use of trench exploration to study ancient seismic sequences of faults is currently a popular method [36; 37]. From the field survey, the overall profile of the trench is 12 m long and 16 m high. By analyzing displacement differences of key stratigraphic layers revealed in the fault profile within the trend, and by identifying markers of normal fault activity (e.g., colluvial wedges), the number of faulting events and their corresponding displacements were determined. Additionally, dating samples were collected from multiple key stratigraphic layers to constrain the timing of fault activity. The trench profile at Qianjiao village exposed five sets of strata and two colluvial wedges (Figure 5). The strata from top to bottom were as follows:  
1. Light yellow loess, deposited as fluvial sediment, with a loose texture, distinct bedding, and locally containing small gravel clasts. 2. Variegated pebble and gravel layer, deposited as fluvial sediment, with distinct layering, locally fine sandy, and a maximum grain size of 22 cm. 3. Yellow clayey loam, deposited as fluvial sediment, with locally distributed fine sandy particles. 4. Compact variegated pebble layer containing clayey loam, indistinct layering, and locally distributed gravel clasts. 5. Compact brownish-yellow to reddish-brown loess with indistinct layering. The \"a\" and \"b\" in Figure 5 are slightly stratified colluvial wedges with a mixture of gravel and silt. Figure 6: Workflow for calculating two-dimensional fractal dimension values of the fault surface morphology. (**a**) Subdivision of units on the bedrock fault surface. N \(\times\) N represents the sliding window size, where N is the product of the number of DEM cells within the sliding window and the length of each DEM cell. (**b**) Fractal dimension values for each calculation unit. (**c**) Mean values of the normal distribution fit for the fractal dimension values of each row calculation unit on the fault surface. The length of the error bars on one side represents the standard deviation of the normal distribution fit for each row calculation unit’s fractal dimension values. The Qianjiao village fault profile revealed a single main fault; all layers within the faulted section showed varying displacements on either side of the fault. By analyzing the varying displacement amounts of corresponding stratigraphic layers on either side of the fault, the stratigraphic displacement record was determined as follows:  
1. The oldest layer exposed in this section is the sedimentary layer 1. 2. Above layer 1, a depositional layer 1 accumulated. Subsequently, a faulting event occurred, displacing both layers 1 and 1. forming colluvial wedge \"a\". 3. After this displacement, depositional layers 1 and 1 accumulated, followed by another faulting event that displaced both layers 1 and 1. 4. The most recent sedimentary layer 1 covers the previous paleoearthquake-induced displacement. The most recent faulting event displaced all the strata, including layer 1, forming colluvial wedge \"b\". Based on optically stimulated luminescence (OSL) dating (Figure 5; Table 2), sample QJC-01 was composed of loose loess from layer 1 and had an age of 7220 \(\pm\) 580 years, while sample QJC-02 consisted of fine sand from layer 1 and had an age of 17,520 \(\pm\) 1440 years. According to the dating results, stratum 1 formed approximately 7220 \(\pm\) 580 years ago. After the formation of stratum 1, one stratigraphic faulting event occurred along the Fushan Fault, displacing stratum 1. The footwall of the fault is currently used as a cultivated field, and the original ground surface has undergone significant erosion owing to human activities. Field investigations revealed that the original ground surface should be at least 0.7 m higher than the current artificially cultivated surface (Figure 4).