Determining the extent of the surface rupture zone associated with historical earthquakes is of critical importance for accurately assessing the seismic hazard impact range, earthquake magnitude, and regional seismic risk. The 1668 Tancheng great earthquake is the largest-magnitude and most destructive historical earthquake ever recorded in eastern China, with its seismogenic structure attributed to the Anqiu–Juxian segment of the Tanlu fault zone. However, the southern terminus of its surface rupture zone has long been debated, with the primary controversy being whether the rupture extended southward across the Tancheng Yaoshang stepover. In this study, based on high-resolution remote sensing image interpretation, we conducted detailed geological surveys and UAV aerial photography on the fault geometry and offset geomorphic features in the Maipo area, located south of the Yaoshang stepover. Combined with Quaternary chronological dating, we determined the detailed characteristics of the latest fault activity and typical coseismic offset landforms in the Maipo area, and analyzed their tectonic implications for the 1668 Tancheng earthquake.

In the northern Maipo area, typical strike-slip surface rupture features are developed, including fault scarps, sag ponds, pressure ridges （earthquake bulges）, and laterally offset gullies, with horizontal right-lateral displacements of 2.0−3.3 m and vertical offsets of 0.25−1.3 m. In the southern Maipo area, a right-lateral horizontal offset of approximately 5.5 m is observed on a gully, along with fractures and an approximately 0.5 m high fault scarp on a piedmont alluvial fan, where a free face is developed on the scarp. Historical earthquake records indicate that the catalog of earthquakes with M≥6 in this region has been complete since 1448. Quaternary geochronological results show that the latest faulting activity postdates approximately 450 years ago. Taken together, these lines of evidence strongly suggest that this surface rupture is highly likely the manifestation of the 1668 Tancheng earthquake.

Integrating the geological evidence with the distribution characteristics of seismic activity, we confirm that the surface rupture zone of this earthquake extends southward to the Maipo–Hezhuang area, attaining a total length of at least 153 km, rather than the previously estimated 130 km. Based on empirical relationships among rupture length, rupture area, and earthquake magnitude, we reassess the moment magnitude of the 1668 Tancheng earthquake to be approximately M_W7.7. In addition, relatively fresh typical strike-slip fault micro-landforms such as earthquake bulges are observed in the northern Maipo area, which may be closely related to the protection by a cohesive meadow layer and weak human activity at this site. This study definitively locates the southern terminus of the surface rupture zone of the 1668 Tancheng earthquake, refines its magnitude parameters, and provides critical geological constraints for future seismic hazard assessment in the southern Tanlu fault zone, including the Xinyi area.