The formation mechanism of the Liantang trough in Qiaojia County along the Jinsha River

The formation mechanism of the broadly NNW-trending Liantang trough, developed along the rear margin of a platform terrace within the Baihetan Hydropower Station reservoir area (Qiaojia County), remains debated. Resolving its formation mechanism is critical for understanding the evolution of the Jinsha River drainage system and for assessing the geotechnical stability of the Liantang resettlement zone. We employed an integrated approach combining field surveys, ultra-deep drilling (> 700 m), wide-field electromagnetic profiling, soil radon measurements, and geochronology to investigate the trough. Our results indicate that: (1) the trough is an eastward-convex tectonic subsidence feature formed after the linkage of the Xiaojiang and Zemuhe Fault; (2) its basement comprises dammed-lake sediments of the Qiaojia pull-apart basin, overlain by debris-flow alluvial and colluvial deposits; (3) subsidence initiated at ~ 290 ka and ceased by ~ 20 ka, with a cumulative fault displacement of ~ 37.5 m. This study establishes a genetic model linking trough development to regional strike-slip faulting and pull-apart basin evolution.