Revisiting surface ruptures of the 1955 Zheduotang earthquake (Mw 7.1) in eastern tibet: kinematic implications on the southern Xianshuihe fault zone

Abstract

Surface ruptures associated with large historical earthquakes provide essential insights into earthquake magnitudes and the kinematics of their seismogenic faults. In 1955, a major earthquake struck Zheduotang Village, Kangding City, producing surface ruptures along the Zheduotang fault, a segment of the southern Xianshuihe fault zone. The magnitude of this event remains a topic of debate, with estimates ranging from M6.6 to M7.5, primarily due to discrepancies in the interpretation of its associated surface ruptures. This study synthesizes previous research on the surface ruptures of the 1955 Zheduotang earthquake and presents new field data, including high-resolution unmanned aerial vehicle (UAV)-based topographic surveys, trenching, and lichenometry in the epicentral region. Analysis of surface rupture freshness, faulting event chronology from trenching, and lichen size measurements collectively support a ∼55 km-long surface rupture zone, corresponding to a moment magnitude (M_w) of ∼7.1 for the 1955 earthquake. Offset glacial landform analysis reveals a late Quaternary left-lateral slip rate of ∼2.5–3.0 mm/yr in the southern segment of the Zheduotang fault, which is lower than the previously documented ∼4 mm/yr in the northern segment. Deformed landforms and surface ruptures indicate that the fault trends NNW and exhibits predominantly left-lateral strike-slip motion in its northern segment, while the southern segment trends NW and includes a notable normal faulting component. Our findings suggest that the Zheduotang fault defines the southwestern boundary of the Bamei-Kangding releasing stepover zone within the southern Xianshuihe left-lateral strike-slip fault zone. These results enhance the understanding of seismic hazards and the tectonic kinematics along the eastern boundary of the Tibetan Plateau.