Spatial Distribution and Geometric Characteristics of the Northern Segment of the Xiadian Fault

The Xiadian Fault is a major active fault along the northern margin of the North China Plain and is widely considered to be closely associated with the 1679 Sanhe–Pinggu M8.0 earthquake. Compared with its central and southern segments, the northern segment of the Xiadian Fault—particularly within the Pinggu area—remains poorly constrained in terms of its spatial distribution, strike variations, and geometric characteristics, which hampers a comprehensive understanding of its tectonic role and seismic hazard implications. In this region, thick Quaternary deposits extensively cover the surface, and the fault is predominantly concealed, resulting in a lack of clear and continuous surface expressions and increased uncertainty in fault identification and precise location.

In this study, the northern segment of the Xiadian Fault is investigated based on a systematic analysis of regional geological and tectonic settings, combined with multiple shallow seismic reflection profiles oriented in different directions. The seismic responses of the fault within Quaternary strata are analyzed to constrain its planar location, strike changes, and spatial continuity in the Pinggu area. The geometric features and possible segmentation of the fault are further examined, and the tectonic mechanisms responsible for observed strike deflections are discussed in the context of the regional stress field and inherited basement structures. The results provide new geophysical constraints on the detailed geometry of the northern segment of the Xiadian Fault and contribute to an improved understanding of seismotectonics and seismic hazard assessment along the northern margin of the North China Plain.