LAUSR

Abstract The Xiadian fault is a crucial seismogenic structure in the North China Plain because of the 1679 A.D. Sanhe–Pinggu M8 earthquake. However, ~12 km of the coseismic surface rupture does not match the worldwide statistical relationship between magnitudes and rupture lengths. Paleoseismicity research can assist in resolving this debate. In this study, the synthesized data from geologic investigations, satellite image interpretations, geomorphic mapping, trench logging and sample dating show that the Xiadian fault undergone strong deformation in the Late Quaternary with a characteristic assemblage of landforms, including linear scarps, troughs, sag ponds, small horsts and grabens, and at least eight paleo-earthquake events can be observed. The coseismic displacements are not exactly the same but instead show a range of variation from ~1.4 ± 0.1 m to ~0.9 ± 0.1 m on average, and the median interval between the strong earthquakes was estimated at ~2820 ± 561 years, with an uncertainty value of 0.199. The quasi-periodicity behavior of the Xiadian fault is not as obvious as that of structures in the plate boundary. The surface rupture traces of the M8 earthquake, which is composed of 6 segments in an echelon pattern with a single length, vary from ~1 km to ~5 km. The asymmetric bell-shaped displacement distribution tends to approach a maximum in the central part in Pangezhuang village while gradually decreasing toward the tips in East Liuhetun and Dongxing villages; this suggests that the surface rupture of this event is may be only ~12 km long, although underlying causes require further study.