Quaternary Activity and Paleoearthquakes of the Fushan Fault, Shanxi, China

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 (coseismic 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.