The Subei triple junction: a complex strike-slip – thrust junction allowing strain transfer from the Altyn-Tagh fault to the Qilian Shan

Slip-rate decrease along the eastern Altyn Tagh fault has long been interpreted as due to strain transfer from the strike-slip fault to the sequential thrust splays of the Qilian Shan. While the 2D kinematics of such strain transfer is now becoming well documented thanks to numerous field studies as well as an increase in geodetic and InSAR data, how the structures connect, interact during large rupturing events and evolve on the long-term is not well known. We focus on the Danghe Nan Shan thrust, a major splay of the Altyn Tagh fault (ATF), at one of these complex fault junctions. Near Subei, the western Danghe Nan Shan thrust comprises two left-stepping faults outlined by fault scarps in front of folded and uplifted alluvial fans and terraces. Age constraints of the accumulated slip of four terraces standing 7–60 m above the present stream bed yield shortening and vertical uplift rates of 0.5 ± 0.1 and 1.1 ± 0.3 mm/yr, respectively, over the last 130 ka on one of the thrust. Overall, about 1-1.4 mm/yr uplift and shortening rates are determined, in agreement with late Miocene long-term exhumation rate estimates. We emphasize the need for precise long-term slip rate determination and understanding the three-dimensional structures of fault connections to evaluate strain transfer between faults and related seismic hazard on these complex fault systems.