Geomorphological and sedimentary records of Late Quaternary activities of Qiaojia-Jinyang segment of Lianfeng fault zone, Southwest China

Lianfeng fault zone (LFZ) in Southwest China has great significance for understanding the seismogenic environment, but its nature and latest active age is still poor constrained up to now. The Qiaojia-Jinyang segment (QJS) of LFZ intersects with Jinsha River; so the well-developed river terraces provide a potential spatio-temporal constrains for recent faulting of QJS. Based on investigation of the terrace deposits along river, this paper makes a detailed logging and dating of the faulting and liquefaction of QJS. Combined previous data, the spatio-temporal sequence of the Late-Quaternary river terraces in the area was redetermined. It is considered that the river terraces T1 (lowest) and T2 at QJS (similar to 10-20 m and 60-70 m, respectively, above the local river level) are roughly developed in the Middle Holocene and the Late Pleistocene, indicating that the valley along QJS was strongly undercut since the Late Pleistocene. Based on the analysis of the morphological characteristics, spatial distribution, material composition and intersecting relationship between the sand veins and the layers, the strong ground motions is preliminarily detected, which indicates the strong seismic activity of the during the Quaternary. Combined with the faulting characteristics and the dating data of strata within the profiles of terrace deposits, it is considered that the LFZ is active at least at QJS, and the latest active time is not earlier than the Early-Middle Holocene. These findings provide a clear geological evidences for the seismicity assessment at LFZ, and help to the understanding of regional tectonic environment and the prevention of earthquake disasters.

Automated summary

This study investigates the Qiaojia-Jinyang segment of Lianfeng fault zone (LFZ) in Southwest China and re-determines the spatio-temporal sequence of Late-Quaternary river terraces in the area. The results indicate that LFZ is active at least at QJS, with the latest activity not earlier than the Early-Middle Holocene. These findings provide clear geological evidence for seismicity assessment in LFZ and contribute to the understanding of regional tectonic environment and earthquake disaster prevention.