Trench Profile Evidence of Late Pleistocene Activity of Lizhuang Fault in Jinpingshan-Xiaojinhe Fault Zone

WANG Hongda; CHEN Lichun; WANG Shihai; YOU Shuisheng; YANG Mingwen; ZHI Tianzi; WANG Wenchao; WANG Duo

doi:10.13512/j.hndz.2025.01.03

Abstract：The NE-trending Yulongxueshan-Jinpingshan-Longmenshan tectonic belt is a geotectonic boundary of class I between the Qiangtang-Sanjiang orogenic system and the Yangtze Block.The southern part of this belt was hit by the 1996 Lijiang MS7.0 earthquake,while the northern part was hit successively by the 2008 Wenchuan MS8.0 earthquake and the 2013 Lushan MS7.0 earthquake.However,earthquakes with M≥6 are not yet recorded in the middle section of this belt.The Jinpingshan-Xiaojinhe fault zone is an important part of the middle section of the Yulongxueshan-Jinpingshan-Longmenshan tectonic belt.Whether it has been active since the Late Quaternary,especially since the Holocene,is the basis for evaluating its subsequent seismic hazards,understanding and discussing the geologic evolution and present activity of the boundary tectonoc belt along the southeastern margin of the Tibetan Plateau.In recent years,with the support of the Sichuan Active Fracture Prospecting Program,1/50 000 active fault mapping has been carried out along the Jinpingshan-Xiaojinhe fault zone,which includes a detailed survey of the geology and geomorphology,geophysical prospecting,and a series of trenching.Then,a large amount of basic data and new evidence have been obtained.The Lizhuang fault is a major branch with relatively strong activity in the Late Quaternary of the Jinpingshan-Xiaojinhe fault zone.On the basis of geological and geomorphological investigations,this paper focuses on the analysis and discussion of four trench profiles and the results of chronological tests.The results reveal that the Lizhuang fault has experienced surface rupturing since the formation of the Yalong River T4 terrace,and its latest faulting is limited to 20-43 ka BP,which is a Late Pleistocene fault.