# Quaternary Activity and Paleoearthquakes of the Fushan Fault, Shanxi, China
###### Abstract  
The AD 1209 M6.5 Fushan earthquake caused significant casualties and damage. The Fushan Fault, forming the boundary between the Linfen Faulted Basin and uplifted Taihang Mountains, may have been the seismogenic fault, but research is lacking. Based on UAV and field surveys, we found that the Fushan Fault has a surface exposure length of 24 km and displaces Holocene strata. Samples from offset layers within a trench showed that the most recent event occurred within the last 7 ka (i.e., Holocene activity) and that the fault has the potential to generate earthquakes exceeding magnitude 7. Since 17 ka (late Quaternary), two significant paleoearthquakes have been identified: (1) between 17 and 7 ka (displacement: 2.04 m, average slip: 0.2 mm/yr) and (2) within the last 7 ka (displacement: 3.93 m, average slip: 0.56 mm/yr). Since the Late Pleistocene, the displacement rate has increased, indicating an increasing potential seismic hazard. These results were confirmed by terrestrial LiDAR; the bedrock fault surface fractal dimensions are consistent with two paleoearthquake events since the late Quaternary (cosesismic displacements of 2.51 and 3.18 m). This article uses an empirical formula to evaluate the potential maximum magnitude of the Fushan Fault based on the relationship between the distribution range of the fault surface and the magnitude. Therefore, the maximum assessed earthquake magnitudes of the Fushan Fault are Ms = 7.07, 6.94, and 7.31. This assessment result basically matches the strength of the 6.5 magnitude Fushan earthquake in 1209 AD. By comparing with historical records, our results confirm that the Fushan Fault was the seismogenic structure responsible for the AD 1209 M6.5 Fushan earthquake. the Pliocene and exhibits a steep loess scarp of up to 70-80 m high, with local sections of Permian and Triassic sandstone and limestone. The fault has shown intermittent activity since the Quaternary [7]. However, the details of the most recent period of activity, that during the Late Pleistocene, have not yet been determined. Figure 1: Earthquake distribution and geological background of the research area. **(a)** Simplified tectonic map of China. The red frame marks the extent of **(b)**. **(b)** Tectonic setting of the Linfen Basin and Shanxi graben system. The black dashed rectangle represents the main study area (see Figure 2 for details). F1: Jiaocheng Fault; F2: Qixian-Dongyang Fault; F3: Taigu Fault; F4: Huoshan Piedmont Fault; F5: Hongdong Fault; F6: Lishi Fault; F7: Luoyunshan Fault; F8: Dayang Fault; F9: Fushan Fault; F10: Hancheng Fault; F11: Northern Fault of Emei table; F12: Southern Fault of Emei table; F13: Northern Zhongtiaoshan Fault; F14: Southern Zhongtiaoshan Fault; F15: Jinhuo Fault. Figure 2: The research framework diagram. Many scholars believe that the North China earthquake catalog is complete for earthquakes with magnitude M \(\geq\) 6.5 since the Hongdong earthquake of magnitude 8 in 1303 [8; 9; 10; 11; 12; 13]. Historical records report an M6.5 earthquake in Fushan County in AD 1209, resulting in significant casualties and property damage [14]. The extent of the damage suggests a magnitude of 6 or higher; however, the causative fault for this historical earthquake remains unclear. At present, there is almost no research on the Fushan Fault and Fushan earthquake. Currently, the assessment of the seismic hazard along the Fushan Fault is mainly based on its seismic activity records. However, incomplete seismic records can lead to an underestimation of the seismic hazard of active faults [15]. To objectively assess the hazard posed by the Fushan Fault, it is essential to study its geometric property, kinematic property, paleoseismic sequence, and seismic recurrence characteristics. The overall research framework of this study is shown in Figure 2.  
In this study, for the first step, we conducted an unmanned aerial vehicle (UAV) survey [16] along the Fushan Fault.